A novel relaxin-like protein discovered in boar seminal vesicle : Binding on sperm plasma membrane and physiological function

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This research project was planned to identify the binding sites on boar sperm for relaxin-like protein, to clarify the nature of the binding sites on the sperm, and to examine possible physiological roles of the binding on the sperm. The outcome of this research is as follows.1. Development of TR-FIA as a novel assay system : This research was successful in developing a new assay system for porcine relaxin by adapting time-resolved fluoroimmunoassay (TR-FIA) introduced recently as a non-RIA format. The assay system was a solid-phase TR-FIA based on competition for a polyclonal anti-relaxin antibody between europium (Eu) -labeled relaxin and test samples. This assay we established had several advantages : the assay had a high sensitivity, the measurement time was completed in only 5 h with one second per sample, no special safety precautions had to be taken, and the precision, reproducibility and accuracy of the assay were satisfactory.2. Identification and nature of the binding sites on boar sperm : This research has clearly demonstrated that relaxin-like protein binds mainly to the acrosomal region of boar spermatozoa, with weaker binding at the midpiece and tail, and the binding sites are the nature of both protein and lipid, suggesting that the protein activates sperm function through a specific receptor.3.Possible physiological roles of the binding on boar sperm : This research has shown that relaxin-like protein acts as cholesterol-docking protein and induces sperm capacitation, suggesting that the protein may have value as a potential marker for predicting sperm fertilizing ability of boars.