Galpha subunit Gpa2 recruits kelch repeat subunits that inhibit receptor-G protein coupling during cAMP-induced dimorphic transitions in Saccharomyces cerevisiae

Mol Biol Cell. 2005 Oct;16(10):4557-71. doi: 10.1091/mbc.e05-05-0403. Epub 2005 Jul 19.

Abstract

All eukaryotic cells sense extracellular stimuli and activate intracellular signaling cascades via G protein-coupled receptors (GPCR) and associated heterotrimeric G proteins. The Saccharomyces cerevisiae GPCR Gpr1 and associated Galpha subunit Gpa2 sense extracellular carbon sources (including glucose) to govern filamentous growth. In contrast to conventional Galpha subunits, Gpa2 forms an atypical G protein complex with the kelch repeat Gbeta mimic proteins Gpb1 and Gpb2. Gpb1/2 negatively regulate cAMP signaling by inhibiting Gpa2 and an as yet unidentified target. Here we show that Gpa2 requires lipid modifications of its N-terminus for membrane localization but association with the Gpr1 receptor or Gpb1/2 subunits is dispensable for membrane targeting. Instead, Gpa2 promotes membrane localization of its associated Gbeta mimic subunit Gpb2. We also show that the Gpa2 N-terminus binds both to Gpb2 and to the C-terminal tail of the Gpr1 receptor and that Gpb1/2 binding interferes with Gpr1 receptor coupling to Gpa2. Our studies invoke novel mechanisms involving GPCR-G protein modules that may be conserved in multicellular eukaryotes.

Publication types

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

MeSH terms

  • Amino Acid Sequence
  • Cell Membrane / metabolism
  • Cyclic AMP / metabolism*
  • GTP-Binding Protein alpha Subunits / metabolism*
  • GTP-Binding Protein beta Subunits / metabolism
  • Lipids / physiology
  • Molecular Sequence Data
  • Protein Structure, Secondary
  • Protein Subunits / metabolism
  • Receptors, G-Protein-Coupled / metabolism*
  • Saccharomyces cerevisiae / metabolism
  • Saccharomyces cerevisiae / physiology*
  • Saccharomyces cerevisiae Proteins / metabolism*
  • Sequence Homology, Amino Acid
  • Signal Transduction

Substances

  • GPR1 protein, S cerevisiae
  • GTP-Binding Protein alpha Subunits
  • GTP-Binding Protein beta Subunits
  • Lipids
  • Protein Subunits
  • Receptors, G-Protein-Coupled
  • Saccharomyces cerevisiae Proteins
  • Cyclic AMP
  • Gpa2 protein, S cerevisiae