@article {2010|1749, title = {A computational study of a recreated {G} protein-{GEF} reaction intermediate competent for nucleotide exchange: fate of the {M}g ion}, journal = {Plos One}, volume = {5}, number = {2}, year = {2010}, month = {feb}, pages = {e9142}, publisher = {Public Library of Science}, abstract = {
Small G-proteins of the superfamily Ras function as molecular switches, interacting with different cellular partners according to their activation state. G-protein activation involves the dissociation of bound GDP and its replacement by GTP, in an exchange reaction that is accelerated and regulated in the cell by guanine-nucleotide exchange factors (GEFs). Large conformational changes accompany the exchange reaction, and our understanding of the mechanism is correspondingly incomplete. However, much knowledge has been derived from structural studies of blocked or inactive mutant GEFs, which presumably closely represent intermediates in the exchange reaction and yet which are by design incompetent for carrying out the nucleotide exchange reaction. In this study we have used comparative modelling to recreate an exchange-competent form of a late, pre-GDP-ejection intermediate species in Arf1, a well-characterized small G-protein. We extensively characterized three distinct models of this intermediate using molecular dynamics simulations, allowing us to address ambiguities related to the mutant structural studies. We observed in particular the unfavorable nature of Mg2+ associated forms of the complex and the establishment of closer Arf1-GEF contacts in its absence. The results of this study shed light on GEF-mediated activation of this small G protein and on predicting the fate of the Mg ion at a critical point in the exchange reaction. The structural models themselves furnish additional targets for interfacial inhibitor design, a promising direction for exploring potentially druggable targets with high biological specificity.
}, doi = {10.1371/journal.pone.0009142}, url = {http://dx.doi.org/10.1371\%2Fjournal.pone.0009142}, author = {M{\'e}riam Ben Hamida{\textendash}Reba\"{\i} and Charles H. Robert} } @article {2010|1736, title = {Consensus {M}odes, a robust description of protein collective motions from multiple-minima normal mode analysis{\textendash}application to the {HIV}-1 protease.}, journal = {Phys. Chem. Chem. Phys.}, volume = {12}, year = {2010}, month = {mar}, pages = {2850{\textendash}2859}, abstract = {Protein flexibility is essential for enzymatic function, ligand binding, and protein-protein or protein-nucleic acid interactions. Normal mode analysis has increasingly been shown to be well suited for studying such flexibility, as it can be used to identify favorable structural deformations that correspond to functional motions. However, normal modes are strictly relevant to a single structure, reflecting a particular minimum on a complex energy surface, and are thus susceptible to artifacts. We describe a new theoretical framework for determining \"consensus\" normal modes from a set of related structures, such as those issuing from a short molecular dynamics simulation. This approach is more robust than standard normal mode analysis, and provides higher collectivity and symmetry properties. In an application to HIV-1 protease, the low-frequency consensus modes describe biologically relevant motions including flap opening and closing that can be used in interpreting structural changes accompanying the binding of widely differing inhibitors.
}, doi = {10.1039/b919148h}, author = {Paulo R. Batista and Charles H. Robert and Jean-Didier Mar{\'e}chal and M{\'e}riam Ben Hamida{\textendash}Reba\"{\i} and Paulo Pascutti and Paulo M. Bisch and David P. Perahia} }