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  • Title: Effects of mutations in the N terminal region of the yeast G protein alpha-subunit Gpa1p on signaling by pheromone receptors.
    Author: Roginskaya M, Connelly SM, Kim KS, Patel D, Dumont ME.
    Journal: Mol Genet Genomics; 2004 Mar; 271(2):237-48. PubMed ID: 14767760.
    Abstract:
    The sites and modes of interaction between G protein-coupled receptors and their cognate heterotrimeric G proteins remain poorly defined. The C-terminus of the Galpha subunit is the best established site of contact of G proteins with receptors, but structural analyses and crosslinking studies suggest the possibility of interactions at the N-terminus of Galpha as well. We screened for mutations in the N-terminal region of the Galpha subunit encoded by the yeast GPA1 gene that specifically affect the ability of the G protein to be activated by the yeast alpha-mating factor receptor. The screen led to identification of substitutions of glutamine or proline for Leu18 of Gpa1p that reduce the response to the pheromones alpha-factor and a-factor without affecting cellular levels of the subunit or its ability to interact with beta and gamma subunits. The mutations do not appear to affect the intrinsic ability of the G protein to be converted to the activated state. The low yield of different mutations with this phenotype indicates either that the N-terminal segment of the yeast Galpha subunit does not undergo extensive interactions with the alpha-factor receptor, or that this region can not be altered without detrimental effects upon the formation of G protein trimers.
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