THE TARGET ANTIGEN FOR GDA-J F3 MONOCLONAL-ANTIBODY IN THE HUMAN SPERM TAIL FIBROUS SHEATH IS A NONCOLLAGENOUS ASIALO-GLYCOPROTEIN - IMPLICATIONS AND SIGNIFICANCE/

Enzymes and chemicals were used to analyse the biochemical structure o f the antigenic epitope recognized by GDA-J/F3 monoclonal antibody (Mo Ab) in the human sperm tail fibrous sheath. Treatment of sperm dried o nto slides with trypsin or dispase enzymes abolished their immunofluor escence staining with GDA-J/F3 MoAb, thus indicating the proteinaceous nature of the antigen. The proteolytic cleavage of GDA-J/F3 protein b y trypsin, which also caused sperm decapitation, indicated the presenc e of peptide bonds involving the carboxyl groups of the basic amino ac ids, arginine and/or lysine. The epitope was also glycosylated as demo nstrated by its sensitivity to sodium metaperiodate treatment which wa s dose-dependent. The GDA-J/F3 antigenic epitope lacked sialic acid si nce pre-treatment of spermatozoa with sialidase enzyme (neuraminidase) had no effect on their reactivity with the antibody. The lack of coll agenous domains in the GDA-J/F3 antigen was demonstrated by the failur e of collagenase to abrogate sperm immunostaining with the MoAb. Furth ermore, type W collagen of the skin basement membrane (BM) was previou sly thought of as a potential target antigen for GDA-J/F3 MoAb. This w as ruled out since several monoclonal and polyclonal antibodies failed to detect the antigen in the spermatozoa using immunofluorescence and Western blotting. These data, therefore, show that the target antigen for GDA-J/F3 MoAb is a non-collagenous asialo-glycoprotein, and by in ference provide the first evidence for the glycosylation of the sheath proteins as another step of post-translational modification occurring during sperm tail development.