@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|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 {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} }