Antimicrobial activity of human seminal plasma and seminal plasma proteins

Abstract: Seminal plasma is semen without the spermatozoa. Human seminal plasma is a complex mixture of secretions from the sex accessory glands, mainly the seminal vesicles and the prostate. Seminal plasma has high protein content and it also contains ions, sugars and low molecular weight components. Immediately after ejaculation the semenogelins and fibronectin aggregate and a coagulum forms trapping the spermatozoa. Seminal plasma is then liquefied as the semenogelins are degraded by prostate specific antigen and the spermatozoa are released. We found that the peptides formed when the semenogelins are degraded were responsible for the major bactericidal activity of seminal plasma. The activity of these peptides was strictly zinc-dependent. We also found potent antifungal activity in seminal unleashed by the acid vaginal pH. The antifungal activity was mediated by beta-microseminoprotein (MSP). The activity of MSP mapped to a region in the C-terminal part of the protein. The antifungal activity was inhibited by calcium binding to MSP at neutral pH but not at the acid vaginal pH explaining the pH-dependent antifungal activity of seminal plasma. This is the first report of antifungal activity of seminal plasma activity and represents novel mechanism of regulation of antifungal activity. We also found that the seminal plasma protein, CRISP-3, possibly had an antifungal activity regulated in pH-dependent manner demonstrating that pH may be a important factor to consider when studying the antimicrobial activity of seminal plasma proteins .