Biochemical and MALDI analysis of the human sperm antigen gp20, homologue of leukocyte CD52

In previous work we demonstrated that gp20, a sialoglycoprotein of human sp erm is homologous to the leukocyte antigen CD52 and that anti-gp20 recogniz es an antigen of the same molecular weight as that recognized by CAMPATH-1 (anti CD52) in leukocytes and sperm, but with some differences. In this stu dy we used anti-gp20 to perform immunoblot analysis of many different sperm , seminal plasma and leukocyte samples. The sperm and seminal plasma antige ns were similar and appeared to consist of two components, whereas the leuk ocyte antigen is unique. Evidence of the presence of two components of the sperm antigen, running respectively at about 19 and 21 kDa, was obtained by analyzing the purified antigen stained with Coomassie brilliant blue and b y immunoblot analysis of the antigen after two-dimensional electrophoresis. Both components had an isoelectric point (pI) between 3 and 6, MALDI analy sis of the purified antigen confirmed the presence of two components and in dicated masses (Mr) of 8243 and 10908. The possible relationship between th ese findings and the presence of two forms of the CD52 gene differing at tw o aminoacids C-terminal to the GPI-anchor site has been discussed. (C) 1999 Academic Press.