Agonist-specific conformational changes in the yeast alpha-factor pheromone receptor.
The yeast alpha-factor pheromone receptor is a member of the G-protein-coupled receptor family. Limited trypsin digestion of yeast membranes was used to investigate ligand-induced conformational changes in this receptor. The agonist, alpha-factor, accelerated cleavage in the third intracellular loop, whereas the antagonist, desTrp1,Ala3-alpha-factor, reduced the cleavage rate. Thus, the enhanced accessibility of the third intracellular loop is specific to the agonist. alpha-Factor inhibited cleavage weakly at a second site near the cytoplasmic terminus of the seventh transmembrane helix, whereas the antagonist showed a stronger inhibition of cleavage at this site and at another site in the C-terminal domain of the receptor. The alpha-factor-induced conformational changes appeared to be inherent properties of the receptor, as they were retained in G-protein-deficient mutants. Moreover, a mutant receptor (ste2-L236H) that affects the third loop and is defective for G-protein coupling retained the ability to undergo the agonist-induced conformational changes. These results are consistent with a model in which G-protein activation is limited by the availability of specific contacts between the G protein and the third intracellular loop of the receptor. The antagonist appears to promote a distinct conformational state that differs from either the unoccupied or the agonist-occupied state.
Büküşoğlu
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Department of Molecular Genetics and Microbiology, University of Massachusetts Medical School, Worcester, 01655-0122, USA.
Jenness
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D000595:Amino Acid Sequence; D005656:Fungal Proteins / Q000819:agonists / Q000737:chemistry* / Q000502:physiology; D019204:GTP-Binding Proteins / Q000378:metabolism; D008024:Ligands; D000072235:Mating Factor; D008969:Molecular Sequence Data; D010455:Peptides / Q000502:physiology; D011485:Protein Binding; D011487:Protein Conformation; D051964:Receptors, Mating Factor; D018000:Receptors, Peptide / Q000819:agonists / Q000737:chemistry*; D014157:Transcription Factors
D005656:Fungal Proteins; D008024:Ligands; D010455:Peptides; D051964:Receptors, Mating Factor; D018000:Receptors, Peptide; D014157:Transcription Factors; D000072235:Mating Factor; D019204:GTP-Binding Proteins