| Summary: | 博士 === 國立臺灣大學 === 生化科學研究所 === 89 === Mouse seminal vesicle secretion contains seven well-defined major proteins designated SVS I-VII in decreasing order of molecular weight. We used various proteases to carry out proteolysis of the protein components of mouse SVS after their resolution in SDS/PAGE copolymerized with gelatin. Only SVS VII was detected in the gel. SVS VII was purified to homogeneity by chromatography and its antiserum was prepared. The primary structure was established using cDNA cloning and confirmed by protein sequencing. Accordingly, it has a theoretical molecular mass of 8538, which was proven by the electrospray mass spectrum. SVS VII consists of 76 amino acid residues in which 10 cysteines are crosslinked into five disulfide bonds. The CD spectrum indicated that the structure of SVS VII was stable over a wide range of pH values but labile after heating.
Result of Western and Northern blot analyses for various tissues indicated that SVS VII protein and its RNA message are expressed only in the seminal vesicle. SVS VII was immunolocalized in luminal epithelium of seminal vesicle. The developmental profile of SVS VII expression in the accessory gland showed no positive correlation with the animal age. Even in the animals that had been castrated, SVS VII and its mRNA remained detectable in the seminal vesicles. A cytochemical study illustrated the presence of the SVS VII-binding region on the entire surface of mouse sperm. We found that the SVS VII-sperm binding was influenced by the salt concentration in the culture medium. The data from binding assay at physiological condition showed that there were two types of SVS VII-binding sites on sperm surface, a high-affinity site with Ka of 5.2x10-6 M-1 and a low-affinity site with Ka of 1.5x10-6 M-1. The SVS VII-sperm binding was inhibited by the dispersed sperm lipids, suggesting the binding sites on spermatozoa are lipid in nature. The results of TLC overlay assay for the binding of 125I-SVS VII to phospholipids and the interaction between SVS VII and phospholipid liposomes demonstrated specific binding of this protein to both phosphatidylethanolamine and phosphatidylserine.
The SVS VII-sperm binding greatly enhanced the sperm motility but did not induce the sperm capacitation. SVS VII after heat treatment could enhance sperm motility initially but immobilized the sperm thereafter. After reductive alkylation, SVS VII lost the ability to enhance motility of sperm.
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