@article {2015|1664, title = {Membrane Protein Structure, Function, and Dynamics: a Perspective from Experiments and Theory.}, journal = {J. Membr. Biol.}, volume = {248}, year = {2015}, publisher = {Biomedical Research Foundation, Academy of Athens, 4 Soranou Ephessiou, 11527, Athens, Greece, zcournia@bioacademy.gr.}, chapter = {611}, abstract = {

Membrane proteins mediate processes that are fundamental for the flourishing of biological cells. Membrane-embedded transporters move ions and larger solutes across membranes; receptors mediate communication between the cell and its environment and membrane-embedded enzymes catalyze chemical reactions. Understanding these mechanisms of action requires knowledge of how the proteins couple to their fluid, hydrated lipid membrane environment. We present here current studies in computational and experimental membrane protein biophysics, and show how they address outstanding challenges in understanding the complex environmental effects on the structure, function, and dynamics of membrane proteins.

}, doi = {10.1007/s00232-015-9802-0}, author = {Cournia, Zoe and Allen, Toby W. and Andricioaei, Ioan and Antonny, Bruno and Baum, Daniel and Grace Brannigan and Buchete, Nicolae-Viorel and Deckman, Jason T. and Delemotte, Lucie and Del Val, Coral and Friedman, Ran and Gkeka, Paraskevi and Hege, Hans-Christian and J{\'e}r{\^o}me H{\'e}nin and Kasimova, Marina A. and Kolocouris, Antonios and Michael L Klein and Khalid, Syma and Lemieux, M Joanne and Lindow, Norbert and Roy, Mahua and Selent, Jana and Mounir Tarek and Tofoleanu, Florentina and Vanni, Stefano and Urban, Sinisa and Wales, David J. and Smith, Jeremy C. and Bondar, Ana-Nicoleta} } @article {2013|1936, title = {Using collective variables to drive molecular dynamics simulations}, journal = {Mol. Phys.}, volume = {111}, number = {22-23}, year = {2013}, pages = {3345{\textendash}3362}, doi = {10.1080/00268976.2013.813594}, author = {Giacomo Fiorin and Michael L Klein and J{\'e}r{\^o}me H{\'e}nin} } @article {2012|1960, title = {General Anesthetics Predicted to Block the {GLIC} Pore with Micromolar Affinity}, journal = {Plos Comput. Biol.}, volume = {8}, number = {5}, year = {2012}, pages = {e1002532}, publisher = {Public Library of Science}, abstract = {

Author Summary

Although general anesthesia is performed every day on thousands of people, its detailed microscopic mechanisms are not known. What is known is that general anesthetic drugs modulate the activity of ion channels in the central nervous system. These channels are proteins that open in response to binding of neurotransmitter molecules, creating an electric current through the cell membrane and thus propagating nerve impulses between cells. One possible mechanism for ion channel inhibition by anesthetics is that the drugs bind inside the pore of the channels, blocking ion current. Here we investigate such a pore block mechanism by computing the strength of the drugs{\textquoteright} interaction with the pore {\textendash} and hence the likelihood of binding, in the case of GLIC, a bacterial channel protein. The results, obtained from numerical simulations of atomic models of GLIC, indicate that the anesthetics isoflurane and propofol have a tendency to bind in the pore that is strong enough to explain blocking of the channel, even at low concentration of the drugs.

}, doi = {10.1371/journal.pcbi.1002532}, url = {http://dx.doi.org/10.1371\%2Fjournal.pcbi.1002532}, author = {LeBard, David N. and J{\'e}r{\^o}me H{\'e}nin and Roderic G Eckenhoff and Michael L Klein and Brannigan, Grace} } @article {2010|1865, title = {An atomistic model for simulations of the general anesthetic isoflurane}, journal = {J. Phys. Chem. B}, volume = {114}, number = {1}, year = {2010}, pages = {604{\textendash}612}, publisher = {Laboratoire d{\textquoteright}Ing{\'e}nierie des Syst{\`e}mes Macromol{\'e}culaires, CNRS, Marseille, France. jhenin@ifr88.cnrs-mrs.fr}, abstract = {An atomistic model of isoflurane is constructed and calibrated to describe its conformational preferences and intermolecular interactions. The model, which is compatible with the CHARMM force field for biomolecules, is based on target quantities including bulk liquid properties, molecular conformations, and local interactions with isolated water molecules. Reference data is obtained from tabulated thermodynamic properties and high-resolution structural information from gas-phase electron diffraction, as well as DFT calculations at the B3LYP level. The model is tested against experimentally known solvation properties in water and oil, and shows quantitative agreement. In particular, isoflurane is faithfully described as lipophilic, yet nonhydrophobic, a combination of properties critical to its pharmacological activity. Intermolecular interactions of the model are further probed through simulations of the binding of isoflurane to a binding site in horse spleen apoferritin (HSAF). The observed binding mode compares well with crystallographic data, and the calculated binding affinities are compatible with experimental results, although both computational and experimental measurements are challenging and provide results with limited precision. The model is expected to be useful for detailed simulations of the elementary molecular processes associated with anesthesia. Full parameters are provided as Supporting Information.}, doi = {10.1021/jp9088035}, author = {J{\'e}r{\^o}me H{\'e}nin and Grace Brannigan and William P Dailey and Roderic G Eckenhoff and Michael L Klein} } @article {2010|1851, title = {Exploring Multidimensional Free Energy Landscapes Using Time-Dependent Biases on Collective Variables}, journal = {J. Chem. Theory Comput.}, volume = {6}, number = {1}, year = {2010}, pages = {35{\textendash}47}, author = {J{\'e}r{\^o}me H{\'e}nin and Giacomo Fiorin and Christophe Chipot and Michael L Klein} } @article {2010|1971, title = {Multiple binding sites for the general anesthetic isoflurane identified in the nicotinic acetylcholine receptor transmembrane domain.}, journal = {Proc. Natl. Acad. Sci. U.s.a.}, volume = {107}, number = {32}, year = {2010}, pages = {14122{\textendash}14127}, abstract = {An extensive search for isoflurane binding sites in the nicotinic acetylcholine receptor (nAChR) and the proton gated ion channel from Gloebacter violaceus (GLIC) has been carried out based on molecular dynamics (MD) simulations in fully hydrated lipid membrane environments. Isoflurane introduced into the aqueous phase readily partitions into the lipid membrane and the membrane-bound protein. Specifically, isoflurane binds persistently to three classes of sites in the nAChR transmembrane domain: (i) An isoflurane dimer occludes the pore, contacting residues identified by previous mutagenesis studies; analogous behavior is observed in GLIC. (ii) Several nAChR subunit interfaces are also occupied, in a site suggested by photoaffinity labeling and thought to positively modulate the receptor; these sites are not occupied in GLIC. (iii) Isoflurane binds to the subunit centers of both nAChR alpha chains and one of the GLIC chains, in a site that has had little experimental targeting. Interpreted in the context of existing structural and physiological data, the present MD results support a multisite model for the mechanism of receptor-channel modulation by anesthetics.}, doi = {10.1073/pnas.1008534107}, author = {Grace Brannigan and David N LeBard and J{\'e}r{\^o}me H{\'e}nin and Roderic G Eckenhoff and Michael L Klein} } @article {2009|1864, title = {Models for phosphatidylglycerol lipids put to a structural test}, journal = {J. Phys. Chem. B}, volume = {113}, number = {19}, year = {2009}, pages = {6958{\textendash}6963}, publisher = {Center for Molecular Modeling, Department of Chemistry, University of Pennsylvania, 231 South 34th Street, Philadelphia, Pennsylvania 19104-6323, USA. jhenin@cmm.chem.upenn.edu}, abstract = {Three atomistic empirical models for phosphatidylglycerol (PG) lipids are tested against structural data in the crystal and liquid crystal states. Simulations of the anhydrous crystal of dimyristoyl-phosphatidylglycerol (DMPG) show that only the CHARMM force field describes the conformation and interactions of PG head groups accurately. The other two models do not reproduce the native network of hydrogen bonds, suggesting the presence of biases in their conformational and nonbonded interaction properties. The CHARMM model is further validated in the biologically relevant liquid crystal phase by comparing experimental small-angle X-ray scattering spectra from DMPG unilamellar vesicles with data calculated from fluid bilayer simulations. The good agreement found in this model-free comparison implies that liquid crystal PG bilayers as described by CHARMM exhibit realistic bilayer thickness and lateral packing. Last, this model is used to simulate a fluid bilayer of palmitoyl-oleoyl-phosphatidylglycerol (POPG). The resulting view of the POPG bilayer structure is at variance with that proposed previously based on simulations, in particular, with respect to lateral packing of head groups and the role of counterions.}, keywords = {chemistry, Crystallography, Lipid Bilayers, Models, Molecular, Phosphatidylglycerols, Scattering, Small Angle, Water, X-Ray}, doi = {10.1021/jp900645z}, author = {J{\'e}r{\^o}me H{\'e}nin and Wataru Shinoda and Michael L Klein} } @article {2008|1970, title = {Embedded cholesterol in the nicotinic acetylcholine receptor}, journal = {Proc. Natl. Acad. Sci. U.s.a.}, volume = {105}, number = {38}, year = {2008}, pages = {14418{\textendash}14423}, publisher = {Center for Molecular Modeling, Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19104, USA. grace@cmm.upenn.edu}, abstract = {The nicotinic acetylcholine receptor (nAChR) is a cation-selective channel central to both neuronal and muscular processes and is considered the prototype for ligand-gated ion channels, motivating a structural determination effort that spanned several decades [Unwin N (2005) Refined structure of the nicotinic acetylcholine receptor at 4 A resolution. J Mol Biol 346:967-989]. Purified nAChR must be reconstituted in a mixture containing cholesterol to function. Proposed modes of interaction between cholesterol and the protein range from specific binding to indirect membrane-mediated mechanisms. However, the underlying cause of nAChR sensitivity to cholesterol remains controversial, in part because the vast majority of functional studies were conducted before a medium resolution structure was reported. We show that the nAChR contains internal sites capable of containing cholesterol, whose occupation stabilizes the protein structure. We detect sites at the protein-lipid interface as conventionally predicted from functional data, as well as deeply buried sites that are not usually considered. Molecular dynamics simulations reveal that occupation of both superficial and deeply buried sites most effectively preserves the experimental structure; the structure collapses in the absence of bound cholesterol. In particular, we find that bound cholesterol directly supports contacts between the agonist-binding domain and the pore that are thought to be essential for activation of the receptor. These results likely apply to those other ion channels within the Cys-loop superfamily that depend on cholesterol, such as the GABA receptor.}, doi = {10.1073/pnas.0803029105}, author = {Grace Brannigan and J{\'e}r{\^o}me H{\'e}nin and Richard Law and Roderic G Eckenhoff and Michael L Klein} } @article {2008|1866, title = {United-Atom Acyl Chains for {CHARMM} Phospholipids}, journal = {J. Phys. Chem. B.}, volume = {112}, number = {23}, year = {2008}, pages = {7008{\textendash}7015}, publisher = {Center for Molecular Modeling, Department of Chemistry, University of Pennsylvania, 231 S. 34th Street, Philadelphia, Pennsylvania 19104-6323, and Research Institute for Computational Sciences, National Institute of Advanced Industrial Science and Technol}, abstract = {In all-atom simulations of lipid membranes, explicit hydrogen atoms contained in the hydrocarbon region are described by a large number of degrees of freedom, although they convey only limited physical information. We propose an implicit-hydrogen model for saturated and monounsaturated acyl chains, aimed at complementing the all-atom CHARMM27 model for phospholipid headgroups. Torsional potentials and nonbonded parameters were fitted to reproduce experimental data and free energy surfaces of all-atom model systems. Comparative simulations of fluid-phase POPC bilayers were performed using the all-hydrogen force field and the present model. The hybrid model accelerates a typical bilayer simulation by about 50\% while sacrificing a minimal amount of detail with respect to the fully atomistic description. In addition, the united-atom description is energetically compatible with all-atom CHARMM models, making it suitable for simulations of complex membrane systems.}, doi = {10.1021/jp800687p}, author = {J{\'e}r{\^o}me H{\'e}nin and Wataru Shinoda and Michael L Klein} }