| Title: | Beta and gamma subunits of a yeast guanine nucleotide-binding protein are not essential for membrane association of the alpha subunit but are required for receptor coupling |
| Address: | "Department of Molecular and Cell Biology, University of California, Berkeley 94720" |
| ISSN/ISBN: | 0027-8424 (Print) 1091-6490 (Electronic) 0027-8424 (Linking) |
| Abstract: | "Conditions were devised to demonstrate GTP-regulated coupling between the yeast STE2-encoded receptor and its cognate guanine nucleotide-binding protein (G protein). Treatment of partially purified membranes with guanosine 5'-[gamma-thio]triphosphate (GTP[gamma-S]) converted the receptor from a high-affinity state (Kd = 17 nM) to a much lower affinity state (Kd approximately 150 nM), as judged by three independent criteria: rate of ligand (alpha-factor) dissociation, equilibrium binding, and antagonist competition. Expression of STE2 from the GAL1 promoter in MATa/MAT alpha diploids, which do not express GPA1 (encoding G protein alpha subunit, G alpha), STE4 (encoding G protein beta subunit, G beta), and STE18 (encoding G protein gamma subunit, G gamma) but do express another G protein alpha subunit (product of GPA2), yielded a single class of low-affinity receptors that were GTP[gamma-S]-insensitive, indicating that STE2 gene product cannot couple productively with other G proteins, even in the absence of competition by its cognate G protein. By using gpa1, STE4, and ste18 mutations, it was found that all three G protein subunits were required for functional coupling, as judged by the absence of high-affinity receptors when any of the three gene products was altered. This finding demonstrates that G beta and G gamma subunits are essential for formation of a productive complex between a G alpha subunit and its corresponding receptor. Wild-type STE4 and STE18 gene products were not essential for membrane localization of the GPA1 gene product, as indicated by cell fractionation and immunological analyses, suggesting that G beta and G gamma subunits interact with the receptor or make the G alpha subunit competent to associate correctly with the receptor, or both" |
| Keywords: | "Cell Membrane/metabolism GTP-Binding Proteins/physiology/*ultrastructure Genes, Fungal Macromolecular Substances Mating Factor Peptides/metabolism Protein Binding Receptors, Cell Surface/*physiology Receptors, Mating Factor *Receptors, Peptide Saccharomyc;" |
| Notes: | "MedlineBlumer, K J Thorner, J eng GM21841/GM/NIGMS NIH HHS/ Research Support, Non-U.S. Gov't Research Support, U.S. Gov't, P.H.S. 1990/06/01 Proc Natl Acad Sci U S A. 1990 Jun; 87(11):4363-7. doi: 10.1073/pnas.87.11.4363" |
