The C terminus of the Saccharomyces cerevisiae alpha-factor receptor contributes to the formation of preactivation complexes with its cognate G protein.
Binding of the alpha-factor pheromone to its G-protein-coupled receptor (encoded by STE2) activates the mating pathway in MATa yeast cells. To investigate whether specific interactions between the receptor and the G protein occur prior to ligand binding, we analyzed dominant-negative mutant receptors that compete with wild-type receptors for G proteins, and we analyzed the ability of receptors to suppress the constitutive signaling activity of mutant Galpha subunits in an alpha-factor-independent manner. Although the amino acid substitution L236H in the third intracellular loop of the receptor impairs G-protein activation, this substitution had no influence on the ability of the dominant-negative receptors to sequester G proteins or on the ability of receptors to suppress the GPA1-A345T mutant Galpha subunit. In contrast, removal of the cytoplasmic C-terminal domain of the receptor eliminated both of these activities even though the C-terminal domain is unnecessary for G-protein activation. Moreover, the alpha-factor-independent signaling activity of ste2-P258L mutant receptors was inhibited by the coexpression of wild-type receptors but not by coexpression of truncated receptors lacking the C-terminal domain. Deletion analysis suggested that the distal half of the C-terminal domain is critical for sequestration of G proteins. The C-terminal domain was also found to influence the affinity of the receptor for alpha-factor in cells lacking G proteins. These results suggest that the C-terminal cytoplasmic domain of the alpha-factor receptor, in addition to its role in receptor downregulation, promotes the formation of receptor-G-protein preactivation complexes.
Dosil
M
M
Department of Molecular Genetics and Microbiology, State University of New York, Stony Brook, New York 11794-5222, USA.
Schandel
K A
KA
Gupta
E
E
Jenness
D D
DD
Konopka
J B
JB
D000483:Alleles; D019943:Amino Acid Substitution; D003593:Cytoplasm / Q000378:metabolism; D044385:GTP-Binding Protein alpha Subunits; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D005799:Genes, Dominant; D005804:Genes, Lethal; D020962:Heterotrimeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism; D008024:Ligands; D009154:Mutation; D051964:Receptors, Mating Factor; D018000:Receptors, Peptide / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D015398:Signal Transduction; D014157:Transcription Factors
D044385:GTP-Binding Protein alpha Subunits; D008024:Ligands; D051964:Receptors, Mating Factor; D018000:Receptors, Peptide; D029701:Saccharomyces cerevisiae Proteins; D014157:Transcription Factors; D019204:GTP-Binding Proteins; C084293:GPA1 protein, S cerevisiae; D043802:GTP-Binding Protein alpha Subunits, Gq-G11; D020962:Heterotrimeric GTP-Binding Proteins