Gβ5-RGS7 selectively inhibits muscarinic M3 receptor signaling via the interaction between the third intracellular loop of the receptor and the DEP domain of RGS7

Regulators of G protein signaling (RGS 1 ) are a diverse family primarily known as GTPase-activating proteins (GAPs) for heterotrimeric G proteins. In addition to the RGS domain, which is responsible for GAP activity, most RGS proteins contain other distinct structural motifs. For example, members of the R7 family of RGS proteins contain a DEP, GGL and novel DHEX domain, and are obligatory dimers with the G protein beta subunit Gβ 5 . Here we show that the Gβ 5 -RGS7 complex can inhibit Ca 2+ mobilization elicited by the muscarinic acetylcholine receptor type 3 (M3R), but not by other Gq-coupled receptors such as M1, M5, histamine H1 and GNRH receptors. Isolated DEP domain of RGS7 is sufficient for the inhibition of M3R signaling, whereas the deletion of the DEP domain renders Gβ5-RGS7 ineffective. Deletion of a portion of the 3 rd intracellular loop allowed the receptor (M3R-short) to signal, but rendered it insensitive to the effect of Gβ 5 -RGS7. Accordingly, recombinant DEP domain bound in vitro to the GST-fused i3 loop of the M3R. These results identify a novel molecular mechanism that can impart receptor-subtype selectivity on signal transduction via Gq-coupled muscarinic receptors.