M. Natochin et al., MUTATIONAL ANALYSIS OF THE ASN RESIDUE ESSENTIAL FOR RGS PROTEIN-BINDING TO G-PROTEINS, The Journal of biological chemistry, 273(12), 1998, pp. 6731-6735
Members of the RGS family serve as GTPase-activating proteins (GAPs) f
or heterotrimeric G-proteins and negatively regulate signaling via G-p
rotein-coupled receptors, The recently resolved crystal structure of R
GS4 bound to G(i) alpha(1) suggests two potential mechanisms for the G
AP activity of RGS proteins as follows: stabilization of the G(i) alph
a(1) switch regions by RGS4 and the catalytic action of RGS4 residue A
sn(128), To elucidate a role of the Asn residue for RGS GAP function,
we have investigated effects of the synthetic peptide corresponding to
the Ga binding domain of human retinal RGS (hRGSr) containing the key
Asn at position 131, and we have carried out mutational analysis of A
sn(131), Synthetic peptide hRGSr-(123-140) retained its ability to bin
d the AlF4--complexed transducin alpha-subunit, G(t) alpha.AlF4-, but
failed to elicit stimulation of Gt alpha GTPase activity, Wild-type hR
GSr stimulated G(t) alpha GTPase activity by similar to 10-fold with a
n EC50 value of 100 nM. Mutant hRGSr proteins with substitutions of As
n(131) by Ser and Gin had a significantly reduced affinity for G(t) al
pha but were capable of substantial stimulation of G(t) alpha GTPase a
ctivity, 80 and 60% of V-max, respectively, Mutants hRGSr-Leu(131), hR
GSr-Ala(131), and hRGSr-Asp(131) were able to accelerate G(t) alpha GT
Pase activity only at very high concentrations (>10 mu m which appears
to correlate with a further decrease of their affinity for transducin
, Two mutants, hRGSr-His(131) and hRGSr-Delta(131), had no detectable
binding to transducin, Mutational analysis of Asn(131) suggests that t
he stabilization of the G-protein switch regions rather than catalytic
action of the Asn residue is a key component for the RGS GAP action.