The target antigen for GDA-J/F3 monoclonal antibody in the human sperm tail fibrous sheath is a non-collagenous asialo-glycoprotein: implications and significance.

Enzymes and chemicals were used to analyse the biochemical structure of the antigenic epitope recognized by GDA-J/F3 monoclonal antibody (MoAb) in the human sperm tail fibrous sheath. Treatment of sperm dried onto slides with trypsin or dispase enzymes abolished their immunofluorescence staining with GDA-J/F3 MoAb, thus indicating the proteinaceous nature of the antigen. The proteolytic cleavage of GDA-J/F3 protein by trypsin, which also caused sperm decapitation, indicated the presence of peptide bonds involving the carboxyl groups of the basic amino acids, arginine and/or lysine. The epitope was also glycosylated as demonstrated by its sensitivity to sodium metaperiodate treatment which was dose-dependent. The GDA-J/F3 antigenic epitope lacked sialic acid since pre-treatment of spermatozoa with sialidase enzyme (neuraminidase) had no effect on their reactivity with the antibody. The lack of collagenous domains in the GDA-J/F3 antigen was demonstrated by the failure of collagenase to abrogate sperm immunostaining with the MoAb. Furthermore, type VII collagen of the skin basement membrane (BM) was previously thought of as a potential target antigen for GDA-J/F3 MoAb. This was 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 inference provide the first evidence for the glycosylation of the sheath proteins as another step of post-translational modification occurring during sperm tail development.