Rhodopsin-family receptors associate with small G proteins to activate phospholipase D

G-protein-coupled receptors of the rhodopsin family transduce many important neural and endocrine signals, These receptors activate heterotrimeric G proteins and in many cases also cause activation of phospholipase D, an enzyme that can be controlled by the small G proteins ARF and RhoA(1-3). Here we show that the activation of phospholipase D that is induced by many, but not all, Ca2+-mobilizing G-protein-coupled receptors is sensitive to inhibitors of ARF and of RhoA. Receptors of this type were coimmunoprecipitated with ARF or RhoA on exposure to agonists, and the effects of GTP analogues on ligand binding to the receptor changed to a profile that is characteristic of small G proteins, These receptors contain the amino-acid sequence Asn-ProXXTyr in their seventh transmembrane domain, whereas receptors capable of activating phospholipase D without involving ARF contain the sequence AspProXXTyr. Mutation of this latter sequence to AsnProXXTyr in the gonadotropin-releasing hormone receptor conferred sensitivity to an inhibitor of ARF, and the reciprocal mutation in the 5-HT2A receptor for 5-hydroxy-tryptamine reduced its sensitivity to the inhibitor, Receptors carrying the AsnProXXTyr motif thus seem to form functional complexes with ARF and RhoA.