SgI-29

Objective: To isolate low-molecular-mass antibacterial mixtures from healthy human seminal plasma. Methods: Semen was obtained by masturbation after at least three days of abstinence from healthy donors. Semen samples were allowed to liquefy at room temperature and then centrifuged at 10,000 r/min for 10 min to separate spermatozoa from seminal plasma. High sensitive antimicrobial activity was measured with radial diffusion assay. Antibacterial activity toward E. coli (ATCC25922) was monitored for each purification steps. The mixture of seminal plasma samples was applied to a SP-Sepharose column. Fractions which showed strong bactericidal activities, were combined and lyophilized. The lyophilized components were dissolved with Milli-Q water and applied to AKTA Superdex 75 column. Peak II of the Superdex 75 column, which showed antibacterial activity and represented the low-molecular-weight cationic fractions of the seminal plasma, was collected and lyophilized. Finally, peak II of the Superdex 75 column was applied to reverse phase HPLC C18 column. Fractions which showed strong antibacterial activity, were lyophilized and store at -20 degrees C. The molecular weight of the low-molecule-mass antibacterial mixtures was determined by Matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. Results: The low-molecular-mass mixtures with obviously higher antibacterial activity, which were termed HSLAMs(Human semen low-molecular-mass antibacterial mixtures), were isolated from the healthy human seminal plasma. Based on the mass spectrometry results, some molecules of RP-HPLC peaks were confirmed to be the semenogelin I derived peptides. Conclusion: The low-molecule-mass antibacterial mixtures may play an important role in males innate immunity. Semenogelin I derived peptides may be one of the sources of the low-molecule-mass antimicrobial mixtures in human seminal plasma.

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 Zn(2+) 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 SgI regarding its association with spermatozoa and the interaction dependency on Zn(2+). The concentration of Zn(2+) 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 SgI binds to spermatozoa in a concentration-dependent and saturable manner. In solution, SgI bound to spermatozoa in a non-Zn(2+)-dependent way, whereas immobilized SgI interacts with spermatozoa only in the presence of Zn(2+). It indicates that SgI must exhibit a specific structure or free flexibility to be able to interact with that ligand. Our results indicate that the association of SgI to spermatozoa is conformation dependent and specific. These findings could constitute a basis for the development of a male contraceptive.

The protease prostate-specific antigen (PSA) is a marker widely used clinically for monitoring prostatic malignancies. Under normal conditions, this enzyme is mainly involved in the post ejaculation degradation of the major human seminal protein, the seminal plasma motility inhibitor precursor/semenogelin I (SPMIP/SgI), which is the predominant protein component of human semen coagulum. PSA primary structure and activity on synthetic substrates predict a chymotrypsin-like activity whose specificity remains to be established. The present study was aimed at characterizing the proteolytic processing of the SPMIP/SgI by PSA. Purified SPMIP/SgI was incubated with PSA in the presence or absence of protease inhibitors. General serine protease inhibitors, heavy metal cations (Zn2+ and Hg2+), and the heavy metal chelator 1,10-phenanthroline partially or totally inhibited the proteolytic activity of PSA toward SPMIP/SgI. Under identical conditions, other proteins, such as bovine serum albumin, ovalbumin, and casein, were very poor substrates for PSA. Hydrolysis products were separated by reverse-phase high-performance liquid chromatography, assayed for sperm motility inhibitory activity, and analyzed by immunoblotting and mass spectrometry. The region responsible for the sperm motility inhibitory activity and containing an SPMI antiserum epitope was localized to the N-terminal portion of the molecule between residues 85 and 136. On the other hand, a monoclonal antibody against a seminal vesicle-specific antigen (MHS-5) recognized fragments derived from the central part of the SPMIP/SgI (residues 198-223). PSA hydrolysis occurred almost exclusively at either leucine or tyrosine residues, demonstrating directly for the first time a restricted chymotrypsin-like activity on a physiological substrate. The results suggest that PSA is the main enzyme responsible for the processing of SPMIP/SgI in human semen and that this protease manifests unusual specificity with respect to hydrolyzable substrates and sites of hydrolysis.