Dissociation of Membrane-Anchored Heterotrimeric G-Protein Induced by Gα Subunit Binding to GTP

Heterotrimeric G-proteins activation on the intracellular Side of the cell membrane is. :initiated by stimulation of the G-Protein Coupled, Receptors (GPCRs) extra-cellular part: This two-step activation mechanism includes'(1) an exchange between GDP and GTP molecules in the G(alpha) subunit and (2) a dissociation of the whole G(alpha beta gamma) complex into two Membrane anchored blocks, namely the isolated G(alpha) and G(beta gamma) subunits. Although X-ray data are available. for :both inactive G(alpha beta gamma):GDP and active G(alpha):GTP. cornplexes; intermediate steps 1 inVOlved in the molecular mechanism of the dissociation have not yet been addressed at the molecular level. In this study, We first huilt a rnembrane-anchored.nteiniediate G(alpha beta gamma):GTP complex. This model was then:. equilibrated by inoleadar. dynamics simulations before the Targeted Molecular Dynamics (TMD) technique was used to force the G(alpha) subunit to evolve from its inactive..(GDP:.-hOund)... to its active (GTP-bound) conformations, as described by available X-ray data The TMD constraint was applied only to the G(alpha) subunit so that the resulting global rearrangements acting on the -whole G(alpha beta gamma):GTP heterotrimer could be analyzed. We showed how these mainly local conformational changes of G(alpha) could Initiate large domain domain motions of the whole complex, the G(beta gamma) behaving as an almost quasi rigid block This separation of the two G(alpha):GTP and G(beta gamma) subunits required the loss of several.:, interactions at the G(alpha):G(beta)gamma interface that were reported. This study provided an atornistic view of the Crucial intermediate step of the G.:proteins activation, e.g:, the dissociation, that could hardly be elucidated by the experiment.