Modulation of the affinity and selectivity of RGS protein interaction with G alpha subunits by a conserved asparagine/serine residue.
The crystal structure of the complex between a G protein alpha subunit (Gi alpha 1) and its GTPase-activating protein (RGS4) demonstrated that RGS4 acts predominantly by stabilization of the transition state for GTP hydrolysis [Tesmer, J. J., et al. (1997) Cell 89, 251]. However, attention was called to a conserved Asn residue (Asn128) that could play a catalytic role by interacting, directly or indirectly, with the hydrolytic water molecule. We have analyzed the effects of several disparate substitutions for Asn128 on the GAP activity of RGS4 toward four G alpha substrates (Go, Gi, Gq, and Gz) using two assay formats. The results substantiate the importance of this residue but indicate that it is largely involved in substrate binding and that its function may vary with different G alpha targets. Various mutations decreased the apparent affinity of RGS4 for substrate G alpha proteins by several orders of magnitude, but had variable and modest effects on maximal rates of GTP hydrolysis when tested with different G alpha subunits. One mutation, N128F, that differentially decreased the GAP activity toward G alpha i compared with that toward G alpha q could be partially suppressed by mutation of the nearby residue in G alpha i to that found in G alpha q (K180P). Detection of GAP activities of the mutants was enhanced in sensitivity up to 100-fold by assay at steady state in proteoliposomes that contain heterotrimeric G protein and receptor.
Posner
B A
BA
Department of Pharmacology, Howard Hughes Medical Institute, University of Texas Southwestern Medical Center, Dallas 75235-9041, USA.
Mukhopadhyay
S
S
Tesmer
J J
JJ
Gilman
A G
AG
Ross
E M
EM
D000818:Animals; D001216:Asparagine / Q000378:metabolism*; D001667:Binding, Competitive / Q000235:genetics; D017124:Conserved Sequence; D003545:Cysteine / Q000235:genetics; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D019204:GTP-Binding Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D020690:GTPase-Activating Proteins; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis; D008239:Lysine / Q000235:genetics; D016297:Mutagenesis, Site-Directed; D011392:Proline / Q000235:genetics; D011485:Protein Binding / Q000235:genetics; D011506:Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D020710:RGS Proteins; D011956:Receptors, Cell Surface / Q000502:physiology; D012694:Serine / Q000378:metabolism*
D020690:GTPase-Activating Proteins; D011506:Proteins; D020710:RGS Proteins; D011956:Receptors, Cell Surface; C085379:rho GTPase-activating protein; C098799:RGS4 protein; D012694:Serine; D001216:Asparagine; D006160:Guanosine Triphosphate; D011392:Proline; D019204:GTP-Binding Proteins; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D008239:Lysine; D003545:Cysteine