Carboxyl-terminal mutations of Gq alpha and Gs alpha that alter the fidelity of receptor activation.
The carboxyl terminus of the G protein alpha subunit is a key determinant of the fidelity of receptor activation. We have previously shown that the Gq alpha subunit (alpha q) can be made to respond to alpha i-coupled receptors by replacing its carboxyl terminus with the corresponding alpha i2, alpha o, alpha z residues. We now extend these findings in three ways: 1) carboxyl-terminal mutations of alpha q/alpha i chimeras show that the critical amino acids are in the -3 and -4 positions, 2) exchange of carboxyl termini between alpha q and alpha z allows activation by receptors appropriate to the carboxyl-terminal residues, and 3) we identify receptors that either do or do not activate the expected carboxyl-terminal chimeras (alpha q/alpha i, alpha q/alpha s, alpha s/alpha q). Replacement of the five carboxyl-terminal amino acids of alpha q with the alpha s sequence permitted an alpha s-coupled receptor (the V2 vasopressin receptor but not the beta 2-adrenergic receptor) to stimulate phospholipase C. Replacement of the five carboxyl-terminal amino acids of alpha z with residues of alpha q permitted certain alpha q-coupled receptors (bombesin and V1a vasopressin receptors but not the oxytocin receptor) to stimulate adenylyl cyclase. Thus, the relative importance of the G alpha carboxyl terminus in permitting coupling to a new receptor depends on the receptor with which it is paired. These studies refine our understanding and provide new tools with which to study the fidelity of receptor/G alpha activation.
Conklin
B R
BR
Department of Medicine, University of California, San Francisco 94143, USA. bruce-conklin.gicd@quickmail.ucsf.edu
Herzmark
P
P
Ishida
S
S
Voyno-Yasenetskaya
T A
TA
Sun
Y
Y
Farfel
Z
Z
Bourne
H R
HR
D000818:Animals; D016466:CHO Cells / Q000502:physiology; D006224:Cricetinae; D004247:DNA / Q000235:genetics; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000235:genetics / Q000502:physiology; D019204:GTP-Binding Proteins / Q000235:genetics* / Q000502:physiology*; D006801:Humans; D046911:Macromolecular Substances; D051379:Mice; D016296:Mutagenesis; D009154:Mutation; D018343:Receptors, Adrenergic, beta-2 / Q000502:physiology; D018004:Receptors, Bombesin / Q000502:physiology; D011956:Receptors, Cell Surface / Q000502:physiology*; D018045:Receptors, Oxytocin / Q000502:physiology; D017483:Receptors, Vasopressin / Q000502:physiology; D010738:Type C Phospholipases / Q000378:metabolism
D046911:Macromolecular Substances; D018343:Receptors, Adrenergic, beta-2; D018004:Receptors, Bombesin; D011956:Receptors, Cell Surface; D018045:Receptors, Oxytocin; D017483:Receptors, Vasopressin; D004247:DNA; D010738:Type C Phospholipases; D019204:GTP-Binding Proteins; D019205:GTP-Binding Protein alpha Subunits, Gs