title: Second site suppressor mutations of a GTPase-deficient G-protein alpha-subunit. Selective inhibition of Gbeta gamma-mediated signaling.
abstract: G proteins transmit signals from cell surface receptors to intracellular effectors. The intensity of the signal is governed by the rates of GTP binding (leading to subunit dissociation) and hydrolysis. Mutants that cannot hydrolyze GTP (e.g. GsalphaQ227L, Gi2alphaQ205L) are constitutively activated and can lead to cell transformation and cancer. Here we have used a genetic screen to identify intragenic suppressors of a GTPase-deficient form of the Galpha in yeast, Gpa1(Q323L). Sequencing revealed second-site mutations in three conserved residues, K54E, R327S, and L353Delta (codon deletion). Each mutation alone results in a complete loss of the beta gamma-mediated mating response in yeast, indicating a dominant-negative mode of inhibition. Likewise, the corresponding mutations in a mammalian Gi2alpha (K46E, R209S, L235Delta) lead to inhibition of Gbeta gamma-mediated mitogen-activated protein (MAP) kinase phosphorylation in cultured cells. The most potent of these beta gamma inhibitors (R209S) has no effect on Gi2alpha-mediated regulation of adenylyl cyclase. Despite its impaired ability to release beta gamma, purified recombinant Gpa1(R327S) is fully competent to bind and hydrolyze GTP. These mutants will be useful for uncoupling Gbeta gamma- and Galpha-mediated signaling events in whole cells and animals. In addition, they serve as a model for drugs that could directly inhibit G protein activity and cell transformation.
authors.affiliation: Department of Pharmacology, Yale University School of Medicine, New Haven, Connecticut 06536, USA.
authors.forename: D M
authors.initials: DM
authors.lastname: Apanovitch
authors.forename: T
authors.initials: T
authors.lastname: Iiri
authors.forename: T
authors.initials: T
authors.lastname: Karasawa
authors.forename: H R
authors.initials: HR
authors.lastname: Bourne
authors.forename: H G
authors.initials: HG
authors.lastname: Dohlman
mesh_terms: D000818:Animals; D001483:Base Sequence; D019556:COS Cells; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D017931:DNA Primers; D004926:Escherichia coli / Q000235:genetics; D020558:GTP Phosphohydrolases / Q000378:metabolism*; D019204:GTP-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D000072235:Mating Factor; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010455:Peptides / Q000378:metabolism; D011487:Protein Conformation; D012441:Saccharomyces cerevisiae / Q000235:genetics; D015398:Signal Transduction
chemical_list: D017931:DNA Primers; D010455:Peptides; D000072235:Mating Factor; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D020558:GTP Phosphohydrolases; D019204:GTP-Binding Proteins