Human Testis-specific Expressed Genes Hsd-3.8 Encoded Protein Function Studies

Fertilization is a complex process which involves the male (spermatozoon) and the female (oocyte) gametes. Successful fertilization is dependent on a well-choreographed series of steps being executed with precise timing and accuracy. Undoubtedly, spermatozoon is one of the most important components. After spermatogenesis, mature sperm must overcome several obstacles and undergo many changes to achieve its destiny. In these processes, many sperm genes are expressed under precise temporal and spatial regulation. Recently, more and more biologists focus on the molecular mechanisms involved in spermatogenesis and fertilization and many key molecules have been found. HSD-3.8 gene is one of such sperm genes found in our lab.HSD-3.8 gene is a testis-specific gene. It is the target antigen of anti-sperm antibodies found in the serum from an infertile woman. A 0.7 kb fragment (HSD-0.7) containing three immunological epitopes of HSD-3.8 gene was initially isolated by screening human testis A.gtll library with serum from the infertile woman. Anti-HSD-3.8 antibodies possess potent sperm agglutinating activity. In the present study, the full length HSD-3.8 cDNA was isolated and sequenced (GenBank accession number: AF311312). The HSD-3.8 gene is located in the chromosome 9, and it can be delineated into 19 exons and 18 introns. The hydrophilicity analysis shows that the deduced polypeptide of HSD-3.8 cDNA is a soluble protein without transmembrane regions. The deduced HSD-3.8 polypeptide contain sequences corresponding to three tetratricopeptide repeat (TPR) regions, a phosphate binding (P)-loop domain, several Casein kinase II phosphorylation sites, Protein kinase C phosphorylation sites and amidation sites. Western blot was performed by using anti-HSD-0.7 polyclonal antibodies as the primary antibody. In human and rat testis extracts, the molecular weight of the protein which could specifically react with the antibodies was about 55-60 kDa. It is assumed that translational or posttranslational modification is needed for the appropriate function of HSD-3.8 encoding protein.Immunization the HSD-0.7 caused infertility in female rats. Phosphorylation analysis shows that HSD-0.7 could be phosphorylated by PKC in vitro. The HSD-0.7 protein could bind to GTP specifically and possess GTPase activity in vitro. These results suggest that HSD-3.8 may act as a G protein or be coupled to a G-protein, capable of inducing GTP/GDP conversion. The previous findings that HSD-3.8 encoding protein is located at the...