Carboxyl-terminal mutations of Gq alpha and Gs alpha that alter the fidelity of receptor activation

Mol Pharmacol. 1996 Oct;50(4):885-90.


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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • CHO Cells / physiology
  • Cricetinae
  • DNA / genetics
  • GTP-Binding Protein alpha Subunits, Gs / genetics
  • GTP-Binding Protein alpha Subunits, Gs / physiology
  • GTP-Binding Proteins / genetics*
  • GTP-Binding Proteins / physiology*
  • Humans
  • Macromolecular Substances
  • Mice
  • Mutagenesis
  • Mutation*
  • Receptors, Adrenergic, beta-2 / physiology
  • Receptors, Bombesin / physiology
  • Receptors, Cell Surface / physiology*
  • Receptors, Oxytocin / physiology
  • Receptors, Vasopressin / physiology
  • Type C Phospholipases / metabolism


  • Macromolecular Substances
  • Receptors, Adrenergic, beta-2
  • Receptors, Bombesin
  • Receptors, Cell Surface
  • Receptors, Oxytocin
  • Receptors, Vasopressin
  • DNA
  • Type C Phospholipases
  • GTP-Binding Proteins
  • GTP-Binding Protein alpha Subunits, Gs