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Abstract

The proteolytic cleavage of a G protein-coupled peptide hormone receptor, the renal V₂ vasopressin receptor, by a plasma membrane proteinase was investigated. In the absence of protease inhibitors during incubation of bovine kidney membranes with a photoreactive vasopressin agonist, V₂ receptor truncation leads to a labeled receptor fragment with M_r 30,000. The V₂ receptor-degrading enzyme could be completely inhibited by zinc ions yielding the native V₂ receptor glycoprotein with M_r 58,000. Studies with inhibitors of metalloendopeptidases involved in peptide hormone metabolism and with peptide substrates spanning the V₂ receptor cleavage site classify the receptor protease as metalloendoproteinase with specificity for longer substrates. Comparison of the NH₂-terminal protein sequence of the truncated M_r 30,000 V₂ receptor with the sequence deduced from the cDNA of the cloned bovine V₂ receptor shows that cleavage occurs between Gln⁹² and Val⁹³ of the second transmembrane helix close to an extracellular agonist binding site. V₂ receptor proteolysis was dependent on the presence of a hormonal ligand. It occurred rapidly after hormone binding and led to a loss of ligand binding properties of the truncated V₂ receptor. The data suggest that the endogenous V₂ receptor-degrading metalloendoproteinase regulates V₂ receptor function. The novel pathway may contribute to the termination of signal transmission.