Fig. 4. Distinct Gi binding model of GABAB.
a, b, Orientations of the α5 helix in Gi protein when coupling to GABAB, cannabinoid receptor 1 (CB1) (class A), glucagon receptor (GCGR) (class B) and smoothened (SMO) (class F). Structures were aligned by the TMDs; only the TMD of GB2 is shown, for clarity. GABAB-bound, yellow; CB1-bound α5, PDB 6N4B; GCGR-bound α5, PDB 6LML; SMO-bound α5, PDB 6OT0. c, Schematics of the two types of pocket that are involved in G-protein recognition. GABAB, green; monomeric GPCR, blue; Gi, yellow. d, Superposition of GABAB-bound Gil with the GDP-bound Gil. GDP-bound Gil, PDB 1GP2. e, Structural comparison of the GABAB-bound Gil with CB1-, GCGR- and SMO-bound Gil. G proteins are coloured as in a, b.