Binding of Semenogelin I to Intact Human Spermatozoa Studied by Flow Cytometry and Surface Plasmon Resonance

Approximately 1 in 10 couples is infertile No definite cause can be found in about 25% of those cases Studies have indicated that seminal vesicle secretion functions as an optimizer of fertilization The Zn2+ binding protein semenogelin I (SgI) represents a major fraction of the proteins present in seminal vesicle fluid and it serves as a structural component of the coagulum that is formed after ejaculation Cleavage of SgI by prostate specific antigen results in liquefaction of the coagulum Fragmented SgI has antibacterial effects and inhibits spermatozoa mobility SgI has also been found complexed to eppin on spermatozoa and this complex has been suggested to be of importance for fertility Here we used flow cytometry and surface plasmon resonance to study Sgl regarding its association with spermatozoa and the interaction dependency on Zn2+ The concentration of Zn2+ in seminal plasma is approximately 100 times higher than in blood plasma and the metal ion is known to change the structure of SgI We found that Sgl binds to spermatozoa in a concentration dependent and saturable manner In solution Sgl bound to spermatozoa in a non Zn2+ dependent way whereas immobilized Sgl interacts with spermatozoa only in the presence of Zn2+ It indicates that Sgl must exhibit a specific structure or free flexibility to be able to interact with that ligand Our results indicate that the association of Sgl to spermatozoa is conformation dependent and specific These findings could constitute a basis for the development of a male contraceptive