title: The C-terminal tail preceding the CAAX box of a yeast G protein gamma subunit is dispensable for receptor-mediated G protein activation in vivo.
abstract: The gamma subunits of heterotrimeric G proteins are required for receptor-G protein coupling. The C-terminal domains of Ggamma subunits can contact receptors and influence the efficiency of receptor-G protein coupling in vitro. However, it is unknown whether receptor interaction with the C terminus of Ggamma is required for signaling in vivo. To address this question, we cloned Ggamma homologs with diverged C-terminal sequences from five species of budding yeast. Each Ggamma homolog functionally replaced the Ggamma subunit of the yeast Saccharomyces cerevisiae (STE18 gene product). Mutagenesis of S. cerevisiae Ste18 likewise indicated that specific C-terminal sequence motifs are not required for signaling. Strikingly, an internal in-frame deletion removing sequences preceding the C-terminal CAAX box of Ste18 did not impair signaling by either of its cognate G protein-coupled pheromone receptors. Therefore, receptor interaction with the C-terminal domain of yeast Ggamma is not required for receptor-mediated G protein activation in vivo. Because the mechanism of G protein activation by receptors is conserved from yeast to humans, mammalian receptors may not require interaction with the tail of Ggamma for G protein activation in vivo. However, receptor-Ggamma interaction may modulate the efficiency of receptor-G protein coupling or promote activation of Gbetagamma effectors that co-cluster with receptors.
authors.affiliation: Department of Cell Biology and Physiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
authors.forename: Sharon L
authors.initials: SL
authors.lastname: Chinault
authors.forename: Kendall J
authors.initials: KJ
authors.lastname: Blumer
mesh_terms: D044388:GTP-Binding Protein gamma Subunits; D017353:Gene Deletion; D020962:Heterotrimeric GTP-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000072235:Mating Factor; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D010455:Peptides / Q000378:metabolism; D017434:Protein Structure, Tertiary; D051964:Receptors, Mating Factor; D018000:Receptors, Peptide / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D014157:Transcription Factors
chemical_list: D044388:GTP-Binding Protein gamma Subunits; D010455:Peptides; D051964:Receptors, Mating Factor; D018000:Receptors, Peptide; C084294:STE18 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D000072235:Mating Factor; D020962:Heterotrimeric GTP-Binding Proteins