Cannabinoid receptor-G protein interactions: Gαi1-bound structures of IC3 and a mutant with altered G protein specificity

摘要

The structure of the C-terminal region of the third cytoplasmic loop (IC3) of the cannabinoid receptor one (CB1) bound to Gαi1 has been determined using transferred nuclear Overhauser effects (NOEs). The wild-type IC3 sequence is helical when associated with Gαi1. In contrast, a peptide containing the amino-acid inversion, Ala³⁴¹-Leu³⁴² adopts a single turn. These findings correlate with the attenuated Gi association of CB1 with the Ala³⁴¹-Leu³⁴² mutation previously observed in vivo and the diminished stimulation of Gαi1 GTPase activity by the corresponding peptide demonstrated in vitro here. These results, the first to report the structure of a GPCR domain while associated with G protein, imply the C-terminus of CB1 IC3, a region with high-sequence conservation among G-protein coupled receptors, must be helical for efficient coupling and activation of the Gi protein.