Genetic and structural analysis of G protein α subunit regulatory domains

Genetic and structural analysis of the α chain polypeptides of heterotrimeric G proteins defines functional domains for GTP/GDP binding, GTPase activity, effector activation, receptor contact and βγ subunit complex regulation. The conservation in sequence comprising the GDP/GTP binding and GTPase domains among G protein α subunits readily allows common mutations to be made for the design of mutant polypeptides that function as constitutive active or dominant negative βγ chains when expressed in different cell types. Organization of the effector activation, receptor and βγ contact domains is similar in the primary sequence of the different α subunit polypeptides relative to the GTP/GDP binding domain sequences. Mutation within common motifs of the different G protein α chain polypeptides have similar functional consequences. Thus, what has been learned with the Gs and Gi proteins and the regulation of adenylyl cyclase can be directly applied to the analysis of newly identified G proteins and their coupling to receptors and regulation of putative effector enzymes.