SEMENOGELIN-I AND SEMENOGELIN-II, THE MAJOR GEL-FORMING PROTEINS IN HUMAN SEMEN, ARE SUBSTRATES FOR TRANSGLUTAMINASE

The major seminal vesicle secreted proteins in human semen. semenogeli n I and semenogelin II, interact non-covalently and via disulphide bri dges to instantly form a coagulum upon ejaculation, The coagulum is li quefied after a few minutes due to the action of a prostatic serine pr otease, prostate-specific antigen (PSA). In contrast to rat semen, whi ch forms an insoluble plug within minutes of expulsion. no transglutam inase-mediated cross-linking has been demonstrated in ejaculated human semen. However, we here show that semenogelin I and semenogelin II. b oth in seminal vesicle fluid and purified from semen. are substrates f or factor XIIIa, the fibrin cross-linking transglutaminase. The cross- linking of the semenogelins, which was conformation-dependent. and the incorporation of a fluorescence-labelled amine, were visualised by SD S/PAGE and Western blot. Purified semenogelin I and semenogelin II cou ld be cross-linked separately into complexes. Moreover. digestion of s emenogelin with PSA produced fragments, some of which were cross-linke d into complexes by factor XIIIa. We also found that PSA was unable to release any semenogelin fragments during exposure of the high molecul ar-mass complexes of cross-linked semenogelin to active PSA.