Characterization of cDNA encoding a human sperm membrane protein sharing homology with Huntingtin protein

In our earlier study, we have reported the identification and characterization of a 57-kDa sperm membrane protein from human spermatozoa. The protein was found to be localized on the acrosome in acrosome intact spermatozoa and shifted to equatorial region after acrosomal induction. Further, we demonstrated that it plays a critical role in sperm-egg binding and fusion. Since the protein was found to be either absent or poorly expressed on the spermatozoa from infertile men, we designated it as Fertility Associated Sperm Antigen (FASA). A human epididymal cDNA library in Lambda-ZAP vector was screened with a polyclonal antibody raised against FASA. A clone was obtained with an insert of ∼1.9 kb cDNA. The sequence showed 99% homology with a part of the human chromosome 11. EST database showed that a portion of 1.9 kb gene has 87% homology to gene encoding Huntington disease protein (HDP). The mutated form of this protein is responsible for Huntington's disease (HD) and is found in the brain cells of HD patients.