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

Abstract

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(α) subunit and (2) a dissociation of the whole G(αβγ) complex into two membrane-anchored blocks, namely the isolated G(α) and G(βγ) subunits. Although X-ray data are available for both inactive G(αβγ):GDP and active G(α):GTP complexes, intermediate steps involved in the molecular mechanism of the dissociation have not yet been addressed at the molecular level. In this study, we first built a membrane-anchored intermediate G(iαβγ):GTP complex. This model was then equilibrated by molecular dynamics simulations before the Targeted Molecular Dynamics (TMD) technique was used to force the G(α) subunit to evolve from its inactive (GDP-bound) to its active (GTP-bound) conformations, as described by available X-ray data. The TMD constraint was applied only to the G(α) subunit so that the resulting global rearrangements acting on the whole G(αβγ):GTP heterotrimer could be analyzed. We showed how these mainly local conformational changes of G(α) could initiate large domain:domain motions of the whole complex, the G(βγ) behaving as an almost quasi-rigid block. This separation of the two G(α):GTP and G(βγ) subunits required the loss of several interactions at the G(α):G(βγ) interface that were reported. This study provided an atomistic view of the crucial intermediate step of the G-proteins activation, e.g., the dissociation, that could hardly be elucidated by the experiment.

Gα73Β is a downstream effector of JAK/STAT signalling and a regulator of Rho1 inDrosophilahaematopoiesis

“…The alpha subunits of heterotrimeric G proteins are the effector units that relay extracellular signals received by G-proteincoupled receptors (GPCRs) to generate a cellular response (Louet et al, 2012). However, in addition to their role in canonical GPCR signalling, recent evidence suggests a more versatile role for Ga subunits.…”

Conformational restriction of G‐proteins Coupled Receptors (GPCRs) upon complexation to G‐proteins: A putative activation mode of GPCRs?

“…Among the ten lowest frequencies normal modes of the protein:protein complex, the modes 8, 12, 13 and 15 were of particular interest because the anti‐symetric rotation motion of the receptor was coupled to four of the five lowest frequencies modes 8, 9, 10 and 11 previously identified for the isolated G‐protein [16]. In this previous study, we described how these G‐protein NM could be linked to its activation, especially to the GDP release and, in another study, the G‐protein dissociation [41]. These observations clearly suggest that the overall dynamical properties of the complex are probably controlled by the heterotrimeric G‐protein and not by the receptor as it could be thought until now.…”

“…2 and corresponded to the mode 8 computed for the isolated receptor. Coupled motions of the G-protein included modes 8, 9, 10 and 11 computed for the isolated G-protein those we previously discussed a putative role in their activation [41].…”