A heparin-binding membrane protein from goat spermatozoa immobilizes spermatozoa in the presence of complement

ObjectiveTo characterize the major membrane protein of goat spermatozoa.DesignBasic research.SettingSamples collected from local slaughterhouse and study conducted in an academic research environment.Patient(s)Goat epididymal tissue.Intervention(s)Goat epididymal tissues were collected immediately after slaughter and the spermatozoa were isolated within 2 hours. Sperm immobilization test was performed with motile spermatozoa at 32°C within 3–4 hours of collection and isolation of the cells.Main Outcome Measure(s)The heparin-binding sperm membrane protein (HBSM) of goat is insensitive to trypsin and its antisera immobilize spermatozoa in presence of complement.Result(s)Forty-two percent of membrane protein could be extracted with 0.25% (wt/vol) 3-[(3-Cholamidopropyl) dimethylammonio]-1-propanesulfonate (CHAPS) from the isolated sperm membrane. By heparin-affinity chromatography, 46% of the extracted protein was recovered. Positive hybridization with radiolabeled heparin on western transfer confirmed the heparin-binding property of the protein (HBSM). Heparin binding to HBSM is an ionic bondage and can be disrupted by 1 M NaCl, as revealed by 86% recovery of the radiolabeled heparin in trichloroacetic acid–precipitated supernatant of [125I] heparin-HBSM conjugate. Heparin-binding sperm membrane protein is localized at the anterior region of the spermatozoal head. No detectable proteolytic fragment of HBSM was detected after limited digestion by trypsin. Heparin-binding sperm membrane protein antisera (1:10,000 titer) developed from rabbit did not recognize the denatured protein. The antisera inhibited spermatozoal motility in a complement-dependent manner.Conclusion(s)We suggest that the heparin-binding motif of the spermatozoal membrane protein might be required in modulation of the spermatozoal motility.