Incorporation of G alpha(z)-specific sequence at the carboxyl terminus increases the promiscuity of G alpha(16) toward G(i)-coupled receptors

Although the promiscuous nature of G(16) allows it to interact with numerou s G protein-coupled receptors, several G(i)-linked receptors are incapable of activating phospholipase C via G(16). A series of chimeras between G alp ha(16) and G alpha(z) were constructed and assayed for their ability to med iate receptor-induced stimulation of phospholipase C. Two G alpha(16/z) chi meras harboring 25 or 44 G alpha(z)-specific sequences at their C termini ( named 16z25 and 16z44) were capable of responding to 14 different G(i)-coup led receptors tested, including those that were either unable to associate with G alpha(16) (melatonin Mel1c) or activate G alpha(16) weakly (mu-opioi d and type 1 somatostatin). Agonist-induced stimulation of phospholipase C was more efficiently mediated (higher maximal and lower EC50 value) by 16z4 4 than by G alpha(16). Both 16z25 and 16z44 were also coupled to G(s)- and G(q)-linked receptors. Incorporation of G alpha(z) sequence at the N termin us of G alpha(16) did not further enhance the ability of the chimeras to in teract with G(i)-coupled receptors. Expression of the various chimeras was verified by immunodetection and functional analysis of their constitutively activated mutants. These results show that the incorporation of alpha 4/be ta 6 and alpha 5 regions of G alpha(z) into a G alpha(16) backbone can impr ove the recognition of G(i)-coupled receptors. G alpha(16/z) chimeras with expanded capability to interact with G(i)-linked receptors may be used to l ink orphan receptors to the stimulation of phospholipase C.