@article {2020|2140, title = {Structural transitions in the RNA 7SK 5{\textquoteright} hairpin and their effect on HEXIM binding}, journal = {Nucleic Acids Res}, volume = {48}, year = {2020}, month = {01}, pages = {373-389}, abstract = {

7SK RNA, as part of the 7SK ribonucleoprotein complex, is crucial to the regulation of transcription by RNA-polymerase II, via its interaction with the positive transcription elongation factor P-TEFb. The interaction is induced by binding of the protein HEXIM to the 5\&$\#$39; hairpin (HP1) of 7SK RNA. Four distinct structural models have been obtained experimentally for HP1. Here, we employ computational methods to investigate the relative stability of these structures, transitions between them, and the effects of mutations on the observed structural ensembles. We further analyse the results with respect to mutational binding assays, and hypothesize a mechanism for HEXIM binding. Our results indicate that the dominant structure in the wild type exhibits a triplet involving the unpaired nucleotide U40 and the base pair A43-U66 in the GAUC/GAUC repeat. This conformation leads to an open major groove with enough potential binding sites for peptide recognition. Sequence mutations of the RNA change the relative stability of the different structural ensembles. Binding affinity is consequently lost if these changes alter the dominant structure.

}, doi = {10.1093/nar/gkz1071}, author = {R{\"o}der, Konstantin and Guillaume Stirnemann and Dock-Bregeon, Anne-Catherine and Wales, David J and Pasquali, Samuela} } @article {2020|2141, title = {Water dynamics at electrified graphene interfaces: a jump model perspective}, journal = {Phys Chem Chem Phys}, year = {2020}, month = {Mar}, abstract = {

The reorientation dynamics of water at electrified graphene interfaces was recently shown [J. Phys. Chem. Lett., 2020, 11, 624-631] to exhibit a surprising and strongly asymmetric behavior: positive electrode potentials slow down interfacial water reorientation, while for increasingly negative potentials water dynamics first accelerates before reaching an extremum and then being retarded for larger potentials. Here we use classical molecular dynamics simulations to determine the molecular mechanisms governing water dynamics at electrified interfaces. We show that changes in water reorientation dynamics with electrode potential arise from the electrified interfaces\&$\#$39; impacts on water hydrogen-bond jump exchanges, and can be quantitatively described by the extended jump model. Finally, our simulations indicate that no significant dynamical heterogeneity occurs within the water interfacial layer next to the weakly interacting graphene electrode.

}, doi = {10.1039/d0cp00359j}, author = {Zhang, Yiwei and Guillaume Stirnemann and Hynes, James T and Laage, Damien} } @article {2019|2139, title = {Effect of Ions on Water Dynamics in Dilute and Concentrated Aqueous Salt Solutions}, journal = {J Phys Chem B}, volume = {123}, year = {2019}, month = {Apr}, pages = {3312-3324}, abstract = {

Aqueous ionic solutions are ubiquitous in chemistry and in biology. Experiments show that ions affect water dynamics, but a full understanding of several questions remains needed: why some salts accelerate water dynamics while others slow it down, why the effect of a given salt can be concentration-dependent, whether the effect of ions is rather local or more global. Numerical simulations are particularly suited to disentangle these different effects, but current force fields suffer from limitations and often lead to a poor description of dynamics in several aqueous salt solutions. Here, we develop an improved classical force field for the description of alkali halides that yields dynamics in excellent agreement with experimental measurements for water reorientational and translational dynamics. These simulations are analyzed with an extended jump model, which allows to compare the effects of ions on local hydrogen-bond exchange dynamics and on more global properties like viscosity. Our results unambiguously show that the ion-induced changes in water dynamics are usually mostly due to a local effect on the hydrogen-bond exchange dynamics; in contrast, the change in viscosity leads to a smaller effect, which governs the retardation only for a minority of salts and at high concentrations. We finally show how the respective importance of these two effects can be directly determined from experimental measurements alone, thus providing guidelines for the selection of an electrolyte with specific dynamical properties.

}, doi = {10.1021/acs.jpcb.9b01053}, author = {Laage, Damien and Guillaume Stirnemann} } @article {2018|2137, title = {Conformational entropy of a single peptide controlled under force governs protease recognition and catalysis}, journal = {Proc Natl Acad Sci U S A}, volume = {115}, year = {2018}, month = {11}, pages = {11525-11530}, abstract = {

An immense repertoire of protein chemical modifications catalyzed by enzymes is available as proteomics data. Quantifying the impact of the conformational dynamics of the modified peptide remains challenging to understand the decisive kinetics and amino acid sequence specificity of these enzymatic reactions in vivo, because the target peptide must be disordered to accommodate the specific enzyme-binding site. Here, we were able to control the conformation of a single-molecule peptide chain by applying mechanical force to activate and monitor its specific cleavage by a model protease. We found that the conformational entropy impacts the reaction in two distinct ways. First, the flexibility and accessibility of the substrate peptide greatly increase upon mechanical unfolding. Second, the conformational sampling of the disordered peptide drives the specific recognition, revealing force-dependent reaction kinetics. These results support a mechanism of peptide recognition based on conformational selection from an ensemble that we were able to quantify with a torsional free-energy model. Our approach can be used to predict how entropy affects site-specific modifications of proteins and prompts conformational and mechanical selectivity.

}, keywords = {enzymology, mechanics, proteases, single molecule, torsional free energy}, doi = {10.1073/pnas.1803872115}, author = {Guerin, Marcelo E and Guillaume Stirnemann and Giganti, David} } @article {2018|2134, title = {DNA Binding Induces a Nanomechanical Switch in the RRM1 Domain of TDP-43}, journal = {J Phys Chem Lett}, volume = {9}, year = {2018}, month = {Jul}, pages = {3800-3807}, abstract = {

Understanding the molecular mechanisms governing protein-nucleic acid interactions is fundamental to many nuclear processes. However, how nucleic acid binding affects the conformation and dynamics of the substrate protein remains poorly understood. Here we use a combination of single molecule force spectroscopy AFM and biochemical assays to show that the binding of TG-rich ssDNA triggers a mechanical switch in the RRM1 domain of TDP-43, toggling between an entropic spring devoid of mechanical stability and a shock absorber bound-form that resists unfolding forces of \∼40 pN. The fraction of mechanically resistant proteins correlates with an increasing length of the TG n oligonucleotide, demonstrating that protein mechanical stability is a direct reporter of nucleic acid binding. Steered molecular dynamics simulations on related RNA oligonucleotides reveal that the increased mechanical stability fingerprinting the holo-form is likely to stem from a unique scenario whereby the nucleic acid acts as a \"mechanical staple\" that protects RRM1 from mechanical unfolding. Our approach highlights nucleic acid binding as an effective strategy to control protein nanomechanics.

}, doi = {10.1021/acs.jpclett.8b01494}, author = {Wang, Yong Jian and Rico-Lastres, Palma and Lezamiz, Ainhoa and Mora, Marc and Solsona, Carles and Guillaume Stirnemann and Garcia-Manyes, Sergi} } @article {2018|2132, title = {The force-dependent mechanism of DnaK-mediated mechanical folding}, journal = {Sci Adv}, volume = {4}, year = {2018}, month = {Feb}, pages = {eaaq0243}, abstract = {

It is well established that chaperones modulate the protein folding free-energy landscape. However, the molecular determinants underlying chaperone-mediated mechanical folding remain largely elusive, primarily because the force-extended unfolded conformation fundamentally differs from that characterized in biochemistry experiments. We use single-molecule force-clamp spectroscopy, combined with molecular dynamics simulations, to study the effect that the Hsp70 system has on the mechanical folding of three mechanically stiff model proteins. Our results demonstrate that, when working independently, DnaJ (Hsp40) and DnaK (Hsp70) work as holdases, blocking refolding by binding to distinct substrate conformations. Whereas DnaK binds to molten globule-like forms, DnaJ recognizes a cryptic sequence in the extended state in an unanticipated force-dependent manner. By contrast, the synergetic coupling of the Hsp70 system exhibits a marked foldase behavior. Our results offer unprecedented molecular and kinetic insights into the mechanisms by which mechanical force finely regulates chaperone binding, directly affecting protein elasticity.

}, doi = {10.1126/sciadv.aaq0243}, author = {Perales-Calvo, Judit and Giganti, David and Guillaume Stirnemann and Garcia-Manyes, Sergi} } @article {2018|2136, title = {Forcing the reversibility of a mechanochemical reaction}, journal = {Nat Commun}, volume = {9}, year = {2018}, month = {08}, pages = {3155}, abstract = {

Mechanical force modifies the free-energy surface of chemical reactions, often enabling thermodynamically unfavoured reaction pathways. Most of our molecular understanding of force-induced reactivity is restricted to the irreversible homolytic scission of covalent bonds and ring-opening in polymer mechanophores. Whether mechanical force can by-pass thermodynamically locked reactivity in heterolytic bimolecular reactions and how this impacts the reaction reversibility remains poorly understood. Using single-molecule force-clamp spectroscopy, here we show that mechanical force promotes the thermodynamically disfavored SN2 cleavage of an individual protein disulfide bond by poor nucleophilic organic thiols. Upon force removal, the transition from the resulting high-energy unstable mixed disulfide product back to the initial, low-energy disulfide bond reactant becomes suddenly spontaneous, rendering the reaction fully reversible. By rationally varying the nucleophilicity of a series of small thiols, we demonstrate how force-regulated chemical kinetics can be finely coupled with thermodynamics to predict and modulate the reversibility of bimolecular mechanochemical reactions.

}, doi = {10.1038/s41467-018-05115-6}, author = {Beedle, Amy E M and Mora, Marc and Davis, Colin T and Snijders, Ambrosius P and Guillaume Stirnemann and Garcia-Manyes, Sergi} } @article {2018|2087, title = {The major β-catenin/E-cadherin junctional binding site is a primary molecular mechano-transductor of differentiation .}, journal = {Elife}, volume = {7}, year = {2018}, month = {2018 07 19}, abstract = {

, the primary molecular mechanotransductive events mechanically initiating cell differentiation remain unknown. Here we find the molecular stretching of the highly conserved Y654-β-catenin-D665-E-cadherin binding site as mechanically induced by tissue strain. It triggers the increase of accessibility of the Y654 site, target of the Src42A kinase phosphorylation leading to irreversible unbinding. Molecular dynamics simulations of the β-catenin/E-cadherin complex under a force mimicking a 6 pN physiological mechanical strain predict a local 45\% stretching between the two α-helices linked by the site and a 15\% increase in accessibility of the phosphorylation site. Both are quantitatively observed using FRET lifetime imaging and non-phospho Y654 specific antibody labelling, in response to the mechanical strains developed by endogenous and magnetically mimicked early mesoderm invagination of gastrulating embryos. This is followed by the predicted release of 16\% of β-catenin from junctions, observed in FRAP, which initiates the mechanical activation of the β-catenin pathway process.

}, keywords = {Amino Acid Sequence, Animals, Armadillo Domain Proteins, Binding Sites, Cadherins, Cell Differentiation, Drosophila melanogaster, Drosophila Proteins, Fluorescence Resonance Energy Transfer, Mechanotransduction, Cellular, Molecular Dynamics Simulation, Phosphorylation, Protein Binding, Protein Conformation, Proto-Oncogene Proteins pp60(c-src), Sequence Homology, Transcription Factors}, issn = {2050-084X}, doi = {10.7554/eLife.33381}, author = {R{\"o}per, Jens-Christian and Mitrossilis, D{\'e}mosth{\`e}ne and Guillaume Stirnemann and Waharte, Fran{\c c}ois and Brito, Isabel and Fernandez-Sanchez, Maria-Elena and Marc Baaden and Salamero, Jean and Farge, Emmanuel} } @article {2018|2135, title = {Segmentation and the Entropic Elasticity of Modular Proteins}, journal = {J Phys Chem Lett}, volume = {9}, year = {2018}, month = {Aug}, pages = {4707-4713}, abstract = {

Single-molecule force spectroscopy utilizes polyproteins, which are composed of tandem modular domains, to study their mechanical and structural properties. Under the application of external load, the polyproteins respond by unfolding and refolding domains to acquire the most favored extensibility. However, unlike single-domain proteins, the sequential unfolding of the each domain modifies the free energy landscape (FEL) of the polyprotein nonlinearly. Here we use force-clamp (FC) spectroscopy to measure unfolding and collapse-refolding dynamics of polyubiquitin and poly(I91). Their reconstructed unfolding FEL involves hundreds of kB T in accumulating work performed against conformational entropy, which dwarfs the \∼30 kB T that is typically required to overcome the free energy difference of unfolding. We speculate that the additional entropic energy caused by segmentation of the polyprotein to individual proteins plays a crucial role in defining the \"shock absorber\" properties of elastic proteins such as the giant muscle protein titin.

}, doi = {10.1021/acs.jpclett.8b01925}, author = {Berkovich, Ronen and Fernandez, Vicente I and Guillaume Stirnemann and Valle-Orero, Jessica and Fernandez, Julio M} } @article {2018|2138, title = {Three Weaknesses for Three Perturbations: Comparing Protein Unfolding Under Shear, Force, and Thermal Stresses}, journal = {J Phys Chem B}, volume = {122}, year = {2018}, month = {Dec}, pages = {11922-11930}, abstract = {

The perturbation of a protein conformation by a physiological fluid flow is crucial in various biological processes including blood clotting and bacterial adhesion to human tissues. Investigating such mechanisms by computer simulations is thus of great interest, but it requires development of ad hoc strategies to mimic the complex hydrodynamic interactions acting on the protein from the surrounding flow. In this study, we apply the Lattice Boltzmann Molecular Dynamics (LBMD) technique built on the implicit solvent coarse-grained model for protein Optimized Potential for Efficient peptide structure Prediction (OPEP) and a mesoscopic representation of the fluid solvent, to simulate the unfolding of a small globular cold-shock protein in shear flow and to compare it to the unfolding mechanisms caused either by mechanical or thermal perturbations. We show that each perturbation probes a specific weakness of the protein and causes the disruption of the native fold along different unfolding pathways. Notably, the shear flow and the thermal unfolding exhibit very similar pathways, while because of the directionality of the perturbation, the unfolding under force is quite different. For force and thermal disruption of the native state, the coarse-grained simulations are compared to all-atom simulations in explicit solvent, showing an excellent agreement in the explored unfolding mechanisms. These findings encourage the use of LBMD based on the OPEP model to investigate how a flow can affect the function of larger proteins, for example, in catch-bond systems.

}, doi = {10.1021/acs.jpcb.8b08711}, author = {Languin-Catto{\"e}n, Olivier and Melchionna, Simone and Philippe Derreumaux and Guillaume Stirnemann and Sterpone, Fabio} } @article {2018|2133, title = {Water dynamics in concentrated electrolytes: Local ion effect on hydrogen-bond jumps rather than collective coupling to ion clusters}, journal = {Proc Natl Acad Sci U S A}, volume = {115}, year = {2018}, month = {05}, pages = {E4953-E4954}, doi = {10.1073/pnas.1803988115}, author = {Guillaume Stirnemann and Jungwirth, Pavel and Laage, Damien} } @article {2017|2024, title = {Ab Initio Simulations of Water Dynamics in Aqueous TMAO Solutions: Temperature and Concentration Effects}, journal = {J Phys Chem B}, year = {2017}, month = {Dec}, abstract = {

We use ab initio molecular dynamics simulation to study the effect of hydrophobic groups on the dynamics of water molecules in aqueous solutions of trimethylamine N-oxide (TMAO). We show that hydrophobic groups induce a moderate (\<2-fold) slowdown of water reorientation and hydrogen-bond dynamics in dilute solutions, but that this slowdown rapidly increases with solute concentration. In addition, the slowdown factor is found to vary very little with temperature, thus suggesting an entropic origin. All of these results are in quantitative agreement with prior classical molecular dynamics simulations and with the previously suggested excluded-volume model. The hydrophilic TMAO headgroup is found to affect water dynamics more strongly than the hydrophobic moiety, and the magnitude of this slowdown is very sensitive to the strength of the water-solute hydrogen-bond.

}, doi = {10.1021/acs.jpcb.7b09989}, author = {Guillaume Stirnemann and Elise Dubou{\'e}-Dijon and Laage, Damien} } @article {2017|2025, title = {Critical structural fluctuations of proteins upon thermal unfolding challenge the Lindemann criterion}, journal = {Proc Natl Acad Sci U S A}, volume = {114}, year = {2017}, month = {Aug}, pages = {9361-9366}, abstract = {

Internal subnanosecond timescale motions are key for the function of proteins, and are coupled to the surrounding solvent environment. These fast fluctuations guide protein conformational changes, yet their role for protein stability, and for unfolding, remains elusive. Here, in analogy with the Lindemann criterion for the melting of solids, we demonstrate a common scaling of structural fluctuations of lysozyme protein embedded in different environments as the thermal unfolding transition is approached. By combining elastic incoherent neutron scattering and advanced molecular simulations, we show that, although different solvents modify the protein melting temperature, a unique dynamical regime is attained in proximity of thermal unfolding in all solvents that we tested. This solvation shell-independent dynamical regime arises from an equivalent sampling of the energy landscape at the respective melting temperatures. Thus, we propose that a threshold for the conformational entropy provided by structural fluctuations of proteins exists, beyond which thermal unfolding is triggered.

}, keywords = {cell thermal stability, Lindemann criterion, Molecular Dynamics Simulation, neutron scattering, protein dynamics}, doi = {10.1073/pnas.1707357114}, author = {Katava, Marina and Guillaume Stirnemann and Zanatta, Marco and Capaccioli, Simone and Pachetti, Maria and Ngai, K L and Sterpone, Fabio and Paciaroni, Alessandro} } @article {2017|2023, title = {Mechanics of Protein Adaptation to High Temperatures}, journal = {J Phys Chem Lett}, volume = {8}, year = {2017}, month = {Dec}, pages = {5884-5890}, abstract = {

Inspired by Somero\&$\#$39;s corresponding state principle that relates protein enhanced thermal stability with mechanical rigidity, we deployed state of the art computational techniques (based on atomistic steered molecular dynamics and Hamiltonian-replica exchange simulations) to study the in silico realization of mechanical and thermal unfolding of two homologous Csp proteins that have evolved to thrive in different thermal environments. By complementing recent single-molecule experiments, we unambiguously show that, for these homologues whose structures are very similar, the increased thermal resistance of the thermophilic variant is not associated with an increased mechanical stability. Our approach provides microscopic insights that are otherwise inaccessible to experimental techniques, and explains why the protein weak spots for thermal and mechanical denaturation are distinct.

}, doi = {10.1021/acs.jpclett.7b02611}, author = {Guillaume Stirnemann and Sterpone, Fabio} } @article {2017|2026, title = {Tailoring protein nanomechanics with chemical reactivity}, journal = {Nat Commun}, volume = {8}, year = {2017}, month = {Jun}, pages = {15658}, abstract = {

The nanomechanical properties of elastomeric proteins determine the elasticity of a variety of tissues. A widespread natural tactic to regulate protein extensibility lies in the presence of covalent disulfide bonds, which significantly enhance protein stiffness. The prevalent in vivo strategy to form disulfide bonds requires the presence of dedicated enzymes. Here we propose an alternative chemical route to promote non-enzymatic oxidative protein folding via disulfide isomerization based on naturally occurring small molecules. Using single-molecule force-clamp spectroscopy, supported by DFT calculations and mass spectrometry measurements, we demonstrate that subtle changes in the chemical structure of a transient mixed-disulfide intermediate adduct between a protein cysteine and an attacking low molecular-weight thiol have a dramatic effect on the protein\&$\#$39;s mechanical stability. This approach provides a general tool to rationalize the dynamics of S-thiolation and its role in modulating protein nanomechanics, offering molecular insights on how chemical reactivity regulates protein elasticity.

}, doi = {10.1038/ncomms15658}, author = {Beedle, Amy E M and Mora, Marc and Lynham, Steven and Guillaume Stirnemann and Garcia-Manyes, Sergi} } @article {2016|2027, title = {Orientational Dynamics of Water at an Extended Hydrophobic Interface}, journal = {J Am Chem Soc}, volume = {138}, year = {2016}, month = {May}, pages = {5551-60}, abstract = {

We report on the orientational dynamics of water at an extended hydrophobic interface with an octadecylsilane self-assembled monolayer on fused silica. The interfacial dangling OH stretch mode is excited with a resonant pump, and its evolution followed in time by a surface-specific, vibrationally resonant, infrared-visible sum-frequency probe. High sensitivity pump-probe anisotropy measurements and isotopic dilution clearly reveal that the decay of the dangling OH stretch excitation is almost entirely due to a jump to a hydrogen-bonded configuration that occurs in 1.61 $\pm$ 0.10 ps. This is more than twice as fast as the jump time from one hydrogen-bonded configuration to another in bulk H2O but about 50\% slower than the reported out-of-plane reorientation at the air/water interface. In contrast, the intrinsic population lifetime of the dangling OH stretch in the absence of such jumps is found to be \>10 ps. Molecular dynamics simulations of air/water and hexane/water interfaces reproduce the fast jump dynamics of interfacial dangling OH with calculated jump times of 1.4 and 1.7 ps for the air and hydrophobic interfaces, respectively. The simulations highlight that while the air/water and hydrophobic/water surfaces exhibit great structural similarities, a small stabilization of the OH groups by the hydrophobic interface produces the pronounced difference in the dynamics of dangling bonds.

}, doi = {10.1021/jacs.6b01820}, author = {Xiao, Shunhao and Figge, Florian and Guillaume Stirnemann and Laage, Damien and McGuire, John A} } @article {2016|1687, title = {Stability and Function at High Temperature. What Makes a Thermophilic GTPase Different from Its Mesophilic Homologue}, journal = {J. Phys. Chem. B}, volume = {120}, year = {2016}, pages = {2721{\textendash}2730}, abstract = {

Comparing homologous enzymes adapted to different thermal environments aids to shed light on their delicate stability/function trade-off. Protein mechanical rigidity was postulated to secure stability and high-temperature functionality of thermophilic proteins. In this work, we challenge the corresponding-state principle for a pair of homologous GTPase domains by performing extensive molecular dynamics simulations, applying conformational and kinetic clustering, as well as exploiting an enhanced sampling technique (REST2). While it was formerly shown that enhanced protein flexibility and high temperature stability can coexist in the apo hyperthermophilic variant, here we focus on the holo states of both homologues by mimicking the enzymatic turnover. We clearly show that the presence of the ligands affects the conformational landscape visited by the proteins, and that the corresponding state principle applies for some functional modes. Namely, in the hyperthermophilic species, the flexibility of the effec...

}, issn = {15205207}, doi = {10.1021/acs.jpcb.6b00306}, author = {Katava, Marina and Kalimeri, Maria and Guillaume Stirnemann and Fabio Sterpone} } @article {2015|1582, title = {The elastic free energy of a tandem modular protein under force.}, journal = {Biochem. Biophys. Res. Comm.}, year = {2015}, pages = {1{\textendash}5}, keywords = {free energy landscape, tandem modular protein}, issn = {0006291X}, doi = {10.1016/j.bbrc.2015.03.051}, url = {http://linkinghub.elsevier.com/retrieve/pii/S0006291X15004866}, author = {Valle-Orero, Jessica and Eckels, Edward and Guillaume Stirnemann and Popa, Ionel and Berkovich, Ronen and Fernandez, Julio M.} } @article {2015|1755, title = {How osmolytes influence hydrophobic polymer conformations: A unified view from experiment and theory.}, journal = {Proc. Natl. Acad. Sci. Usa}, volume = {112}, year = {2015}, pages = {9270{\textendash}5}, abstract = {

It is currently the consensus belief that protective osmolytes such as trimethylamine N-oxide (TMAO) favor protein folding by being excluded from the vicinity of a protein, whereas denaturing osmolytes such as urea lead to protein unfolding by strongly binding to the surface. Despite there being consensus on how TMAO and urea affect proteins as a whole, very little is known as to their effects on the individual mechanisms responsible for protein structure formation, especially hydrophobic association. In the present study, we use single-molecule atomic force microscopy and molecular dynamics simulations to investigate the effects of TMAO and urea on the unfolding of the hydrophobic homopolymer polystyrene. Incorporated with interfacial energy measurements, our results show that TMAO and urea act on polystyrene as a protectant and a denaturant, respectively, while complying with Tanford-Wyman preferential binding theory. We provide a molecular explanation suggesting that TMAO molecules have a greater thermodynamic binding affinity with the collapsed conformation of polystyrene than with the extended conformation, while the reverse is true for urea molecules. Results presented here from both experiment and simulation are in line with earlier predictions on a model Lennard-Jones polymer while also demonstrating the distinction in the mechanism of osmolyte action between protein and hydrophobic polymer. This marks, to our knowledge, the first experimental observation of TMAO-induced hydrophobic collapse in a ternary aqueous system.

}, keywords = {Atomic Force, Computer Simulation, Hydrophobic and Hydrophilic Interactions, Mechanical, Methylamines, Methylamines: chemistry, Microscopy, Molecular Dynamics Simulation, Normal Distribution, Polymers, Polymers: chemistry, Polystyrenes, Polystyrenes: chemistry, Protein Binding, Protein Conformation, Protein Folding, Proteins, Proteins: chemistry, Software, Solvents, Solvents: chemistry, Stress, Thermodynamics, Urea, Urea: chemistry, Water, Water: chemistry}, isbn = {1215421109}, issn = {1091-6490}, doi = {10.1073/pnas.1511780112}, url = {http://www.pnas.org/content/112/30/9270}, author = {Mondal, Jagannath and Halverson, Duncan and Li, Isaac T S and Guillaume Stirnemann and Walker, Gilbert C and Berne, Bruce J} } @article {2015|1729, title = {The mechanochemistry of copper reports on the directionality of unfolding in model cupredoxin proteins.}, journal = {Nature Comm.}, volume = {6}, year = {2015}, pages = {7894}, abstract = {

Understanding the directionality and sequence of protein unfolding is crucial to elucidate the underlying folding free energy landscape. An extra layer of complexity is added in metalloproteins, where a metal cofactor participates in the correct, functional fold of the protein. However, the precise mechanisms by which organometallic interactions are dynamically broken and reformed on (un)folding are largely unknown. Here we use single molecule force spectroscopy AFM combined with protein engineering and MD simulations to study the individual unfolding pathways of the blue-copper proteins azurin and plastocyanin. Using the nanomechanical properties of the native copper centre as a structurally embedded molecular reporter, we demonstrate that both proteins unfold via two independent, competing pathways. Our results provide experimental evidence of a novel kinetic partitioning scenario whereby the protein can stochastically unfold through two distinct main transition states placed at the N and C termini that dictate the direction in which unfolding occurs.

}, isbn = {doi:10.1038/ncomms8894}, issn = {2041-1723}, doi = {10.1038/ncomms8894}, url = {http://www.nature.com/ncomms/2015/150803/ncomms8894/abs/ncomms8894.html}, author = {Beedle, Amy E M and Lezamiz, Ainhoa and Guillaume Stirnemann and Garcia-Manyes, Sergi} } @article {2015|1677, title = {Recovering protein thermal stability using all-atom Hamiltonian replica-exchange simulations in explicit solvent}, journal = {J. Chem. Theo. Comput.}, volume = {11}, year = {2015}, pages = {5573{\textendash}5577}, abstract = {

The REST2 method is successfully applied to investigate the thermal stability of chignolin CLN025 and of Trp-cage. As opposed to temperature replica exchange, REST2 relies on the rescaling of the protein potential energy, which allows a smaller number of replicas. The shape of the stability curve reconstructed on the basis of the corresponding-state principle is in very good agreement with experimental data; for chignolin, the effect of mutations is also recovered.

}, issn = {15499626}, doi = {10.1021/acs.jctc.5b00954}, author = {Guillaume Stirnemann and Fabio Sterpone} } @article {2014|1751, title = {How force unfolding differs from chemical denaturation.}, journal = {Proc. Natl. Acad. Sci. U.s.a}, volume = {111}, year = {2014}, pages = {3413{\textendash}8}, abstract = {

Single-molecule force spectroscopies are remarkable tools for studying protein folding and unfolding, but force unfolding explores protein configurations that are potentially very different from the ones traditionally explored in chemical or thermal denaturation. Understanding these differences is crucial because such configurations serve as starting points of folding studies, and thus can affect both the folding mechanism and the kinetics. Here we provide a detailed comparison of both chemically induced and force-induced unfolded state ensembles of ubiquitin based on extensive, all-atom simulations of the protein either extended by force or denatured by urea. As expected, the respective unfolded states are very different on a macromolecular scale, being fully extended under force with no contacts and partially extended in urea with many nonnative contacts. The amount of residual secondary structure also differs: A significant population of $\alpha$-helices is found in chemically denatured configurations but such helices are absent under force, except at the lowest applied force of 30 pN where short helices form transiently. We see that typical-size helices are unstable above this force, and $\beta$-sheets cannot form. More surprisingly, we observe striking differences in the backbone dihedral angle distributions for the protein unfolded under force and the one unfolded by denaturant. A simple model based on the dialanine peptide is shown to not only provide an explanation for these striking differences but also illustrates how the force dependence of the protein dihedral angle distributions give rise to the worm-like chain behavior of the chain upon force.

}, keywords = {Chemical, Hydrogen-Ion Concentration, Models, Molecular Dynamics Simulation, Protein Conformation, Protein Denaturation, Protein Folding, Protein Unfolding, Ubiquitin, Ubiquitin: chemistry, Urea, Urea: chemistry}, issn = {1091-6490}, url = {http://www.ncbi.nlm.nih.gov/pubmed/24550471}, author = {Guillaume Stirnemann and Kang, Seung-gu and Zhou, Ruhong and Berne, Bruce J} } @article {2013|1752, title = {Elasticity, structure, and relaxation of extended proteins under force.}, journal = {Proc. Natl. Acad. Sci. U.s.a}, volume = {110}, year = {2013}, pages = {3847{\textendash}52}, abstract = {

Force spectroscopies have emerged as a powerful and unprecedented tool to study and manipulate biomolecules directly at a molecular level. Usually, protein and DNA behavior under force is described within the framework of the worm-like chain (WLC) model for polymer elasticity. Although it has been surprisingly successful for the interpretation of experimental data, especially at high forces, the WLC model lacks structural and dynamical molecular details associated with protein relaxation under force that are key to the understanding of how force affects protein flexibility and reactivity. We use molecular dynamics simulations of ubiquitin to provide a deeper understanding of protein relaxation under force. We find that the WLC model successfully describes the simulations of ubiquitin, especially at higher forces, and we show how protein flexibility and persistence length, probed in the force regime of the experiments, are related to how specific classes of backbone dihedral angles respond to applied force. Although the WLC model is an average, backbone model, we show how the protein side chains affect the persistence length. Finally, we find that the diffusion coefficient of the protein{\textquoteright}s end-to-end distance is on the order of 10(8) nm(2)/s, is position and side-chain dependent, but is independent of the length and independent of the applied force, in contrast with other descriptions.

}, keywords = {Atomic Force, Biophysical Phenomena, Computer Simulation, Elasticity, Mechanical, Microscopy, Models, Molecular, Molecular Dynamics Simulation, Proteins, Proteins: chemistry, Stress, Ubiquitin, Ubiquitin: chemistry}, issn = {1091-6490}, url = {http://www.pnas.org/content/early/2013/02/13/1300596110.abstract}, author = {Guillaume Stirnemann and Giganti, David and Fernandez, Julio M and Berne, B J} } @article {2013|1670, title = {Mechanisms of acceleration and retardation of water dynamics by ions}, journal = {J. Am. Chem. Soc.}, volume = {135}, year = {2013}, pages = {11824{\textendash}11831}, abstract = {

There are fundamental and not yet fully resolved questions concerning the impact of solutes, ions in particular, on the structure and dynamics of water, which can be formulated as follows: Are the effects of ions local or long-ranged? Is the action of cations and anions on water cooperative or not? Here, we investigate how the reorientation and hydrogen-bond dynamics of water are affected by ions in dilute and concentrated aqueous salt solutions. By combining simulations and analytic modeling, we first show that ions have a short-ranged influence on the reorientation of individual water molecules and that depending on their interaction strength with water, they may accelerate or slow down water dynamics. A simple additive picture combining the effects of the cations and anions is found to provide a good description in dilute solutions. In concentrated solutions, we show that the average water reorientation time ceases to scale linearly with salt concentration due to overlapping hydration shells and structural rearrangements which reduce the translational displacements induced by hydrogen-bond switches and increase the solution viscosity. This effect is not ion-specific and explains why all concentrated salt solutions slow down water dynamics. Our picture, which is demonstrated to be robust vis-a-vis a change in the force-field, reconciles the seemingly contradictory experimental results obtained by ultrafast infrared and NMR spectroscopies, and suggests that there are no long-ranged cooperative ion effects on the dynamics of individual water molecules in dilute solutions.

}, issn = {00027863}, author = {Guillaume Stirnemann and Wernersson, Erik and Jungwirth, Pavel and Laage, Damien} } @article {2013|1689, title = {When Does Trimethylamine N-Oxide Fold a Polymer Chain and Urea Unfold It?}, journal = {J. Phys. Chem. B}, volume = {117}, year = {2013}, pages = {8723{\textendash}8732}, abstract = {

Longstanding mechanistic questions about the role of protecting osmolyte trimethylamine N-oxide (TMAO) that favors protein folding and the denaturing osmolyte urea are addressed by studying their effects on the folding of uncharged polymer chains. Using atomistic molecular dynamics simulations, we show that 1 M TMAO and 7 M urea solutions act dramatically differently on these model polymer chains. Their behaviors are sensitive to the strength of the attractive dispersion interactions of the chain with its environment: when these dispersion interactions are sufficiently strong, TMAO suppresses the formation of extended conformations of the hydrophobic polymer as compared to water while urea promotes the formation of extended conformations. Similar trends are observed experimentally for real protein systems. Quite surprisingly, we find that both protecting and denaturing osmolytes strongly interact with the polymer, seemingly in contrast with existing explanations of the osmolyte effect on proteins. We show that what really matters for a protective osmolyte is its effective depletion as the polymer conformation changes, which leads to a negative change in the preferential binding coefficient. For TMAO, there is a much more favorable free energy of insertion of a single osmolyte near collapsed conformations of the polymer than near extended conformations. By contrast, urea is preferentially stabilized next to the extended conformation and thus has a denaturing effect.

}, isbn = {15206106}, url = {http://pubs.acs.org/doi/abs/10.1021/jp405609j$\backslash$nhttp://pubs.acs.org/doi/pdf/10.1021/jp405609j$\backslash$nhttp://dx.doi.org/10.1021/jp405609j}, author = {Mondal, Jagannath and Guillaume Stirnemann and Berne, B J} } @article {2012|1676, title = {Communication: On the origin of the non-Arrhenius behavior in water reorientation dynamics}, journal = {J. Chem. Phys.}, volume = {137}, year = {2012}, abstract = {

We combine molecular dynamics simulations and analytic modeling to determine the origin of the non-Arrhenius temperature dependence of liquid water{\textquoteright}s reorientation and hydrogen-bond dynamics between 235 K and 350 K. We present a quantitative model connecting hydrogen-bond exchange dynamics to local structural fluctuations, measured by the asphericity of Voronoi cells associated with each water molecule. For a fixed local structure the regular Arrhenius behavior is recovered, and the global anomalous temperature dependence is demonstrated to essentially result from a continuous shift in the unimodal structure distribution upon cooling. The non-Arrhenius behavior can thus be explained without invoking an equilibrium between distinct structures. In addition, the large width of the homogeneous structural distribution is shown to cause a growing dynamical heterogeneity and a non-exponential relaxation at low temperature.

}, issn = {00219606}, author = {Guillaume Stirnemann and Laage, Damien} } @article {2012|1488, title = {Magnitude and molecular origin of water slowdown next to a protein}, journal = {J. Am. Chem. Soc.}, volume = {134}, year = {2012}, pages = {4116{\textendash}4119}, abstract = {

Hydration shell dynamics plays a critical role in protein folding and biochemical activity and has thus been actively studied through a broad range of techniques. While all observations concur with a slowdown of water dynamics relative to the bulk, the magnitude and molecular origin of this retardation remain unclear. Via numerical simulations and theoretical modeling, we establish a molecular description of protein hydration dynamics and identify the key protein features that govern it. Through detailed microscopic mapping of the water reorientation and hydrogen-bond (HB) dynamics around lysozyme, we first determine that 80\% of the hydration layer waters experience a moderate slowdown factor of \~{}2-3, while the slower residual population is distributed along a power-law tail, in quantitative agreement with recent NMR results. We then establish that the water reorientation mechanism at the protein interface is dominated by large angular jumps similar to the bulk situation. A theoretical extended jump model is shown to provide the first rigorous determination of the two key contributions to the observed slowdown: a topological excluded-volume factor resulting from the local protein geometry, which governs the dynamics of the fastest 80\% of the waters, and a free energetic factor arising from the water-protein HB strength, which is especially important for the remaining waters in confined sites at the protein interface. These simple local factors are shown to provide a nearly quantitative description of the hydration shell dynamics.

}, issn = {00027863}, author = {Fabio Sterpone and Guillaume Stirnemann and Laage, Damien} } @article {2012|1753, title = {Rate limit of protein elastic response is tether dependent}, journal = {Proc. Natl. Acad. Sci. U.s.a.}, volume = {109}, year = {2012}, pages = {14416{\textendash}14421}, abstract = {

The elastic restoring force of tissues must be able to operate over the very wide range of loading rates experienced by living organisms. It is surprising that even the fastest events involving animal muscle tissues do not surpass a few hundred hertz. We propose that this limit is set in part by the elastic dynamics of tethered proteins extending and relaxing under a changing load. Here we study the elastic dynamics of tethered proteins using a fast force spectrometer with sub-millisecond time resolution, combined with Brownian and Molecular Dynamics simulations. We show that the act of tethering a polypeptide to an object, an inseparable part of protein elasticity in vivo and in experimental setups, greatly reduces the attempt frequency with which the protein samples its free energy. Indeed, our data shows that a tethered polypeptide can traverse its free-energy landscape with a surprisingly low effective diffusion coefficient D(eff) \~{} 1,200 nm(2)/s. By contrast, our Molecular Dynamics simulations show that diffusion of an isolated protein under force occurs at D(eff) \~{} 10(8) nm(2)/s. This discrepancy is attributed to the drag force caused by the tethering object. From the physiological time scales of tissue elasticity, we calculate that tethered elastic proteins equilibrate in vivo with D(eff) \~{} 10(4)-10(6) nm(2)/s which is two to four orders magnitude smaller than the values measured for untethered proteins in bulk.

}, issn = {0027-8424}, author = {Berkovich, R. and Hermans, R. I. and Popa, I. and Guillaume Stirnemann and Garcia-Manyes, S. and Berne, B. J. and Fernandez, J. M.} } @article {2012|1684, title = {Water jump reorientation and ultrafast vibrational spectroscopy}, journal = {J. Photochem. Photobiol. A}, volume = {234}, year = {2012}, pages = {75{\textendash}82}, abstract = {

The reorganization of water{\textquoteright}s hydrogen-bond (HB) network by breaking and making HBs lies at the heart of many of the pure liquid{\textquoteright}s special features and many aqueous media phenomena, including chemical reactions, ion transport and protein activity. An essential role in this reorganization is played by water molecule reorientation, long described by very small angular displacement Debye rotational diffusion. A markedly contrasting picture has been recently proposed, based on simulation and analytic modeling: a sudden, large amplitude jump mechanism, in which the reorienting water molecule rapidly exchanges HB partners in an activated process which has all the hallmarks of a chemical reaction. In this contribution, we offer a brief review of the jump mechanism together with a discussion of its application to, and probing by, modern ultrafast infrared spectroscopy experiments. Special emphasis is given to the direct characterization of the jumps via pioneering two-dimensional infrared spectroscopic measurements. ?? 2012 Elsevier B.V. All rights reserved.

}, keywords = {Hydrogen-bond dynamics, Pump-probe infrared spectroscopy, Two-dimensional infrared spectroscopy, Water dynamics}, issn = {10106030}, author = {Laage, Damien and Guillaume Stirnemann and Hynes, James T.} } @article {2012, title = {Water Jump Reorientation: From Theoretical Prediction to Experimental Observation}, journal = {Acc. Chem. Res.}, volume = {45}, number = {1}, year = {2012}, pages = {53{\textendash}62}, doi = {10.1021/ar200075u}, author = {Laage, Damien and Guillaume Stirnemann and Sterpone, Fabio and Hynes, James T.} } @article {2011|1690, title = {Dynamics of water in concentrated solutions of amphiphiles: Key roles of local structure and aggregation}, journal = {J. Phys. Chem. B}, volume = {115}, year = {2011}, pages = {3254{\textendash}3262}, abstract = {

Water translational and reorientational dynamics in concentrated solutions of amphiphiles are investigated through molecular dynamics simulations and analytic modeling. We evidence the critical importance of the solute concentration in determining the magnitude of the slowdown in water dynamics compared to the bulk situation. The comparison of concentrated aqueous solutions of tetramethylurea, which tends to aggregate, and of trimethylamine N-oxide, which does not, shows the dramatic impact of solute clustering on the water dynamics. No significant decoupling of the reorientation and translation dynamics of water is observed, even at very high solute concentrations. The respective roles of energetic and topological disorders in determining the translational subdiffusive water dynamics in these confining environments are discussed. The water reorientational dynamics is shown to be quantitatively described by an extended jump model which combines two factors determined by the local structure: the transition-state excluded volume and the transition-state hydrogen-bond strength.

}, issn = {15206106}, author = {Guillaume Stirnemann and Fabio Sterpone and Laage, Damien} } @article {2011|1738, title = {Non-monotonic dependence of water reorientation dynamics on surface hydrophilicity: competing effects of the hydration structure and hydrogen-bond strength}, journal = {Phys. Chem. Chem. Phys.}, volume = {13}, year = {2011}, pages = {19911}, abstract = {

The reorientation dynamics of interfacial water molecules was recently shown to change non-monotonically next to surfaces of increasing hydrophilicity, with slower dynamics next to strongly hydrophobic (apolar) and very hydrophilic surfaces, and faster dynamics next to surfaces of intermediate hydrophilicities. Through a combination of molecular dynamics simulations and analytic modeling, we provide a molecular interpretation of this behavior. We show that this non-monotonic dependence arises from two competing effects induced by the increasing surface hydrophilicity: first a change in the hydration structure with an enhanced population of water OH bonds pointing toward the surface and second a strengthening of the water-surface interaction energy. The extended jump model, including the effects due to transition-state excluded volume and transition-state hydrogen-bond strength, provides a quasi-quantitative description of the non-monotonic changes in the water reorientation dynamics with surface hydrophilicity.

}, issn = {1463-9076}, author = {Guillaume Stirnemann and Castrillon, Santiago Romero-Vargas and Hynes, James T. and Rossky, Peter J. and Debenedetti, Pablo G. and Laage, Damien} } @article {2011|1383, title = {Reorientation and Allied Dynamics in Water and Aqueous Solutions}, journal = {Annu. Rev. Phys. Chem.}, volume = {62}, year = {2011}, pages = {395{\textendash}416}, abstract = {

The reorientation of a water molecule is important for a host of phenomena, ranging over?in an only partial listing?the key dynamic hydrogen-bond network restructuring of water itself, aqueous solution chemical reaction mechanisms and rates, ion transport in aqueous solution and membranes, protein folding, and enzymatic activity. This review focuses on water reorientation and related dynamics in pure water, and for aqueous solutes with hydrophobic, hydrophilic, and amphiphilic character, ranging from tetramethylurea to halide ions and amino acids. Attention is given to the application of theory, simulation, and experiment in the probing of these dynamics, in usefully describing them, and in assessing the description. Special emphasis is placed on a novel sudden, large-amplitude jump mechanism for water reorientation, which contrasts with the commonly assumed Debye rotational diffusion mechanism, characterized by small-amplitude angular motion. Some open questions and directions for further research are also discussed. Expected final online publication date for the Annual Review of Physical Chemistry Volume 62 is March 31, 2011. Please see http://www.annualreviews.org/catalog/pubdates.aspx for revised estimates.

}, isbn = {0066-426X 1545-1593}, issn = {0066-426X}, doi = {doi: 10.1146/annurev.physchem.012809.103503}, url = {http://www.annualreviews.org/doi/abs/10.1146/annurev.physchem.012809.103503$\backslash$nhttp://www.annualreviews.org.login.ezproxy.lib.purdue.edu/doi/pdf/10.1146/annurev.physchem.012809.103503}, author = {Laage, Damien and Guillaume Stirnemann and Fabio Sterpone and Rey, Rossend and Hynes, James T.} } @article {2011|1691, title = {On the reorientation and hydrogen-bond dynamics of Alcohols}, journal = {J. Phys. Chem. B}, volume = {115}, year = {2011}, pages = {12173{\textendash}12178}, abstract = {

The mechanism of the OH bond reorientation in liquid methanol and ethanol is examined. It is found that the extended jump model, recently developed for water, describes the OH reorientation in these liquids. The slower reorientational dynamics in these alcohols compared to water can be explained by two key factors. The alkyl groups on the alcohol molecules exclude potential partners for hydrogen bonding exchanges, an effect that grows with the size of the alkyl chain. This increases the importance of the reorientation of intact hydrogen bonds, which also slows with increasing size of the alcohol and becomes the dominant reorientation pathway.

}, issn = {15206106}, author = {Vartia, Anthony A. and Mitchell-Koch, Katie R. and Guillaume Stirnemann and Laage, Damien and Thompson, Ward H.} } @article {2011|1739, title = {Water reorientation dynamics in the first hydration shells of F- and I-}, journal = {Phys. Chem. Chem. Phys.}, volume = {13}, year = {2011}, pages = {19895}, abstract = {

Molecular dynamics and analytic theory results are presented for the reorientation dynamics of first hydration shell water molecules around fluoride and iodide anions. These ions represent the extremes of the (normal) halide series in terms of their size and conventional structure-making and -breaking categorizations. The simulated reorientation times are consistent with NMR and ultrafast IR experimental results. They are also in good agreement with the theoretical predictions of the analytic Extended Jump Model. Analysis through this model shows that while sudden, large amplitude jumps (in which the reorienting water exchanges hydrogen-bond partners) are the dominant reorientation pathway for the I(-) case, they are comparatively less important for the F(-) case. In particular, the diffusive reorientation of an intact F(-)...H(2)O hydrogen-bonded pair is found to be most important for the reorientation time, a feature related to the greater hydrogen-bond strength for the F(-)...H(2)O pair. The dominance of this effect for e.g. multiply charged ions is suggested.

}, issn = {1463-9076}, author = {Boisson, Jean and Guillaume Stirnemann and Laage, Damien and Hynes, James T.} } @article {2010|1696, title = {Direct evidence of angular jumps during water reorientation through two-dimensional infrared anisotropy}, journal = {J. Phys. Chem. Lett.}, volume = {1}, year = {2010}, pages = {1511{\textendash}1516}, abstract = {

Water reorientation was recently suggested via simulations to proceed through large angular jumps, but direct experimental evidence has so far remained elusive. Here we show that both infrared pump-probe and photon echo spectroscopies can provide such evidence through the measurement of the two-dimensional anisotropy decay. We calculate these two-dimensional anisotropies from simulations and show they can be interpreted as a vibrational frequency-dependent resolved orientation time-correlation function. We develop a frequency-dependent extended jump model to predict the nature of the angular jump signature in these anisotropies. This model provides a rigorous and unambiguous connection between ultrafast infrared experimental results and the presence of angular jumps in bulk water, and calls for new experiments.

}, issn = {19487185}, doi = {10.1021/jz100385r}, author = {Guillaume Stirnemann and Laage, Damien} } @article {2010|1692, title = {Water hydrogen bond dynamics in aqueous solutions of amphiphiles}, journal = {J. Phys. Chem. B}, volume = {114}, year = {2010}, pages = {3052{\textendash}3059}, abstract = {

The hydrogen bond dynamics of water in a series of amphiphilic solute solutions are investigated through simulations and analytic modeling with an emphasis on the interpretation of experimentally accessible two-dimensional infrared (2D IR) photon echo spectra. We evidence that for most solutes the major effect in the hydration dynamics comes from the hydrophilic groups. These groups can retard the water dynamics much more significantly than can hydrophobic groups by forming strong hydrogen bonds with water. By contrast, hydrophobic groups are shown to have a very moderate effect on water hydrogen bond breaking kinetics. We also present the first calculation of the 2D IR spectra for these solutions. While 2D IR spectroscopy is a powerful technique to probe water hydrogen bond network fluctuations, interpretations of aqueous solution spectra remain ambiguous. We show that a complementary approach through simulations and calculation of the spectra lifts the ambiguity and provides a clear connection between the simulated molecular picture and the experimental spectroscopy data. For amphiphilic solute solutions, we show that, in contrast with techniques such as NMR or ultrafast anisotropy, 2D IR spectroscopy can discriminate between waters next to the solutes hydrophobic and hydrophilic groups. We also evidence that the water dynamics slowdown due to the hydrophilic groups is dramatically enhanced in the 2D IR spectral relaxation, because these groups can induce a slow chemical exchange with the bulk, even when recognized exchange signatures are absent. Implications for the understanding of water around chemically heterogeneous systems such as protein surfaces and for the interpretation of 2D IR spectra in these cases are discussed.

}, issn = {15206106}, author = {Guillaume Stirnemann and Hynes, James T. and Laage, Damien} } @article {2010|1832, title = {Water hydrogen-bond dynamics around amino acids: the key role of hydrophilic hydrogen-bond acceptor groups}, journal = {J. Phys. Chem. B}, volume = {114}, number = {5}, year = {2010}, pages = {2083{\textendash}9}, abstract = {

Water hydrogen-bond (HB) dynamics around amino acids in dilute aqueous solution is investigated through molecular dynamics simulations and analytic modeling. We especially highlight the critical role played by hydrophilic HB acceptors: the strength of the HB formed with water has a pronounced effect on the HB dynamics, in accord with several experimental observations. In contrast, we evidence that hydrophilic HB donors induce a moderate slowdown in the water HB exchange dynamics due to an excluded volume effect, similar to that of hydrophobic groups. We present an analytic model which rationalizes the effect of all examined amino acid sites on the HB dynamics and whose predictions are in excellent agreement with the numerical simulations. This model provides the acceleration or retardation in the HB exchange time with respect to the bulk through the combination of the solute excluded volume factor with the solute-water HB strength factor, both referring to the HB exchange transition state.

}, author = {Sterpone, Fabio and Guillaume Stirnemann and Hynes, James T and Laage, Damien} } @article {2010|1649, title = {Water reorientation, hydrogen-bond dynamics and 2D-IR spectroscopy next to an extended hydrophobic surface.}, journal = {Farad. Discuss.}, volume = {146}, year = {2010}, pages = {263{\textendash}281}, abstract = {

The dynamics of water next to hydrophobic groups is critical for several fundamental biochemical processes such as protein folding and amyloid fiber aggregation. Some biomolecular systems, like melittin or other membrane-associated proteins, exhibit extended hydrophobic surfaces. Due to the strain these surfaces impose on the hydrogen (H)-bond network, the water molecules shift from the clathrate-like arrangement observed around small solutes to an anticlathrate-like geometry with some dangling OH bonds pointing toward the surface. Here we examine the water reorientation dynamics next to a model hydrophobic surface through molecular dynamics simulations and analytic modeling. We show that the water OH bonds lying next to the hydrophobic surface fall into two subensembles with distinct dynamical reorientation properties. The first is the OH bonds tangent to the surface; these exhibit a behavior similar to the water OHs around small hydrophobic solutes, i.e. with a moderate reorientational slowdown explained by an excluded volume effect due to the surface. The second is the dangling OHs pointing toward the surface: these are not engaged in any H-bond, reorient much faster than in the bulk, and exhibit an unusual anisotropy decay which becomes negative for delays of a few picoseconds. The H-bond dynamics, i.e. the exchanges between the different configurations, and the resulting anisotropy decays are analyzed within the analytic extended jump model. We also show that a recent spectroscopy technique, two-dimensional time resolved vibrational spectroscopy (2D-IR), can be used to selectively follow the dynamics of dangling OHs, since these are spectrally distinct from H-bonded ones. By computing the first 2D-IR spectra of water next to a hydrophobic surface, we establish a connection between the spectral dynamics and the dynamical properties that we obtain directly from the simulations.

}, issn = {1359-6640}, author = {Guillaume Stirnemann and Rossky, Peter J and Hynes, James T and Laage, Damien} } @article {2009|1693, title = {Why water reorientation slows without iceberg formation around hydrophobic solutes}, journal = {J. Phys. Chem. B}, volume = {113}, year = {2009}, pages = {2428{\textendash}2435}, abstract = {

The dynamics of water molecules next to hydrophobic solutes is investigated, specifically addressing the recent controversy raised by the first time-resolved observations, which concluded that some water molecules are immobilized by hydrophobic groups, in strong contrast to previous NMR conclusions. Through molecular dynamics simulations and an analytic jump reorientation model, we identify the water reorientation mechanism next to a hydrophobic solute and provide evidence that no water molecules are immobilized by hydrophobic solutes. Their moderate rotational slowdown compared to bulk water (e.g., by a factor of less than 2 at low solute concentration) is mainly due to slower hydrogen-bond exchange. The slowdown is quantitatively described by a solute excluded volume effect at the transition state for the key hydrogen-bond exchange in the reorientation mechanism. We show that this picture is consistent with both ultrafast anisotropy and NMR experimental results and that the transition state excluded volume theory yields quantitative predictions of the rotational slowdown for diverse hydrophobic solutes of varying size over a wide concentration range. We also explain why hydrophobic groups slow water reorientation less than do some hydrophilic groups.

}, author = {Laage, Damien and Guillaume Stirnemann and Hynes, James T.} } @article {2008|1695, title = {Does water condense in hydrophobic cavities? A molecular simulation study of hydration in heterogeneous nanopores}, journal = {J. Phys. Chem. C}, volume = {112}, year = {2008}, pages = {10435{\textendash}10445}, author = {Cailliez, Fabien and Guillaume Stirnemann and Boutin, Anne and Demachy, Isabelle and Fuchs, Alain H.} }