Cell biology of semenogelin.

Semenogelin is the predominant protein in human semen. It is synthetised by the secretory epithelium of the seminal vesicles as a 461 amino acid precursor protein. Following cleavage of a predominantly hydrophobic signal peptide, the secreted protein contains 439 amino acid residues. The amino acid sequence of semenogelin has a repetitive structure, but it displays no significant homology to any other characterized translation product. In the seminal vesicle secretion, semenogelin occurs in disulphide-linked high molecular mass complexes together with two less abundant 71 and 76 kDa proteins. These proteins have a very close antigenic and structural relationship to semenogelin, but contrary to semenogelin one or both of these semenogelin-related proteins are also expressed by the secretory epithelium of the epididymis. Semenogelin and the semenogelin-related proteins are the major proteins involved in the gelatinous entrapment of ejaculated spermatozoa. Antigenic epitopes common to these proteins are localised to the locomotive parts of the spermatozoa. The spermatozoa become progressively motile when gel-forming proteins are fragmented by the kallikrein-like protease, prostate-specific antigen, and the gel dissolves.