STRUCTURAL HETEROGENEITY, POSTTRANSLATIONAL MODIFICATIONS, AND BIOLOGICAL-ACTIVITIES OF SV-IV, A MAJOR PROTEIN SECRETED FROM THE RAT SEMINAL-VESICLE EPITHELIUM

The primary structure of purified SV-IV, a major secretory protein syn thesized by the rat seminal vesicle (SV) epithelium, was analysed by e lectrospray mass spectrometry (ES-MS). The protein was found to be hig hly heterogeneous, The various components were separated and identifie d by reversed phase high-performance liquid chromatography (HPLC) on l ine with ES-MS. Structural characterization of the SV-IV cyanogen brom ide digests revealed the occurrence of a Val/Met substitution in about 50% of the purified protein molecules. We suggest that this mutation is the expression of a genetic polymorphism. Other minor components, c orresponding to structural changes (fragmentation, deletion, and phosp horylation) of SV-IV and probably doe to post-translational modificati ons of the native protein, were also detected. In particular, by using protein tyrosine phosphatase hydrolysis combined with ES-MS, we demon strated that, in the phosphorylated species of SV-IV, a single phospha te group was covalently bound to the Tyr-36 residue. The significance of these findings in relation to the regulation of important biologica l processes, such as immune response, blood coagulation, inflammatory reaction, and mammalian reproduction, are discussed. (C) 1997 by John Wiley & Sons, Ltd.