Sperm Acrosome Associated Protein 1 (SPACA1)

The deduced 294-amino acid protein has a calculated molecular mass of 32 kD and contains a signal peptide, 3 potential casein kinase II phosphorylation sites, and a C-terminal transmembrane domain. Mass spectrometry analysis showed that the serine-256 site was phosphorylated in vivo. Northern blot analysis of human tissues detected a 1.5-kb transcript in testis only. RNA dot-blot hybridization of 76 tissues confirmed the testis-specific expression.

Immunofluorescence studies of noncapacitated human spermatozoa localized SPACA1 to the principal segment and equatorial segment of the acrosome, and immunogold studies confirmed localization to the inner acrosomal membrane of the sperm equatorial segment.