Engineering a V(2) vasopressin receptor agonist- and regulator of G-protein-signaling-sensitive G protein.
It is extremely difficult to detect guanine nucleotide exchange or hydrolysis stimulated by receptors which couple to G(s)alpha. Furthermore, G(s)alpha is largely resistant to the GTPase-activating properties of RGS proteins. Coexpression of the vasopressin V(2) receptor with a series of chimeric G protein alpha subunits in which the C-terminal 6-12 amino acids of G(i1)alpha were replaced with the equivalent sequence of G(s)alpha allowed robust vasopressin-stimulated [(35)S]GTPgammaS binding. Vasopressin did not stimulate the GTPase activity of fusion proteins between the V(2) receptor and either G(s)alpha or G(i1)alpha. However, it produced a concentration-dependent stimulation of V(max) for a V(2) receptor-G(i1)alpha/Gs6alpha fusion protein. This construct bound [(3)H]vasopressin with high affinity and this was competed by other ligands with rank order anticipated for the V(2) receptor. RGS1 enhanced vasopressin stimulation of V(2) receptor-G(i1)alpha/G(s)6alpha in a concentration-dependent manner. RGS-GAIP was substantially less potent. Enzyme kinetic analysis demonstrated that RGS1 increased both V(max) of the GTPase activity and the observed K(m) for GTP, consistent with RGS1 accelerating the rate of GTP hydrolysis of the chimeric G protein, whereas the agonist vasopressin accelerates guanine nucleotide exchange. This approach provides a sensitive assay for V(2) receptor agonist ligands and may be amenable to many other G(s)alpha-coupled receptors.
Feng
Gui-Jie
GJ
Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow, Scotland, United Kingdom.
Cavalli
Antonella
A
Milligan
Graeme
G
D000595:Amino Acid Sequence; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D020962:Heterotrimeric GTP-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D011485:Protein Binding; D015202:Protein Engineering / Q000379:methods*; D017483:Receptors, Vasopressin / Q000819:agonists*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction; D014162:Transfection
D017483:Receptors, Vasopressin; D011993:Recombinant Fusion Proteins; D020962:Heterotrimeric GTP-Binding Proteins