Coupling of a single receptor to two different G proteins in the signal transduction of FMRFamide-related peptides.

A series of studies, which have investigated the membrane receptor-mediated signal transduction of PDVDHVFLRFamide in the locust oviduct, suggest the presence of a novel ligand-receptor reaction system. In this system, inhibitory peptides and stimulatory peptides share a single receptor by having the same binding sequence, VFLRFamide, but are able to produce opposite muscle responses due to the differences in activation sites. In this research, the results from both "guanine nucleotide effect assay" and GTPase assay indicated that the receptors for the inhibitory and stimulatory FMRFamide-related peptides (FaRPs) are coupled with G proteins and both inhibitory and excitatory effects of FaRPs on locust oviduct are through the activation of G proteins. Thus it is very likely that the receptor is coupled with two different G proteins. The activation of one is responsible for the inhibitory effect and the activation of the other is responsible for the stimulatory effect.