Mechanisms of inter- and intramolecular communication in GPCRs and G proteins

This study represents the first attempt to couple, by computational experiments, the mechanisms of intramolecular and intermolecular communication concerning a guanidine nucleotide exchange factor (GEF), the thromboxane A2 receptor (TXA2R), and the cognate G protein (Gq) in its heterotrimeric GDP-bound state. Two-way pathways mediate the communication between the receptor-G protein interface and both the agonist binding site of the receptor and the nucleotide binding site of the G protein. The increase in solvent accessibility in the neighborhoods of the highly conserved E/DRY receptor motif, in response to agonist binding, is instrumental in favoring the penetration of the C-terminus of Gq\u3b1 in between the cytosolic ends of H3, H5, and H6. The arginine of the E/DRY motif is predicted to be an important mediator of the intramolecular and intermolecular communication involving the TXA2R. The receptor-G protein interface is predicted to involve multiple regions from the receptor and the G protein \u3b1-subunit. However, receptor contacts with the C-terminus of the \u3b15-helix seem to be the major players in the receptor-catalyzed motion of the \u3b1-helical domain with respect to the Ras-like domain and in the formation of a nucleotide exit route in between the \u3b1F-helix and \u3b26/\u3b15 loop of Gq \u3b1. The inferences from this study are of wide interest, as they are expected to apply to the whole rhodopsin family, given also the considerable G protein promiscuity. \ua9 2008 American Chemical Society