Partial amino acid sequencing of 80-kDa human sperm antigen (80-kDa HSA)

An 80-kDa human sperm antigen (80-kDa HSA) has been identified as a sperm p rotein responsible for inducing immunoinfertility. Immunization with the pu rified protein induced infertility in male and female rats. Immunohistochem ical and immunofluorescent studies have demonstrated that the antigen is sp ecific to spermatozoa. The present study describes the partial amino acid s equencing of 80-kDa HSA. The homogeneous protein was electrophoretically tr ansferred onto a PVDF membrane and the excised band of 80-kDa HSA was used to determine the partial N-terminal amino acid sequence. The protein was th en subjected to enzymatic digestion with endoproteinase Lys-C and endoprote inase Glu-C. The partial amino acid sequence of the major peptides thus obt ained was determined. The digestion with endoproteinase Lys-C generated 4 m ajor peptides, two of which showed partial sequence homology with lactoferr in. Endoproteinase Glu-C digestion produced 3 major peptides. The sequences of the 2 peptides were determined for which no matches were found in the d atabank. These results confirmed earlier observations that 80-kDa HSA is a sperm-specific protein that is chemically distinct from any other protein i nvolved in normal physiological process. Earlier studies have demonstrated that it is antigenic, efficacious, conserved, and could be a promising cand idate for the development of an antifertility vaccine.