Sperm Acrosome Associated Protein 3 (SPACA3)

The deduced 215-amino acid SPACA3 protein has a calculated molecular mass of 23.4 kD. SPACA3 contains a putative transmembrane region followed by a predicted protease cleavage site between an ala-lys linkage, a signature sequence for the alpha-lactalbumin/lysozyme C (LYZ) protein family, 3 predicted N-terminal and 1 C-terminal myristoylation sites, and 2 phosphorylation sites. SPACA3 shares 53% and 52% identity with monkey stomach lysozyme and human lysozyme, respectively. Northern blot analysis of human tissues detected a 1.0-kb transcript in testis only. Immunofluorescent studies localized SPACA3 to the sperm head acrosome and equatorial segment, and immunogold staining detected SPACA3 distribution over the entire acrosomal matrix, including the principal and equatorial segments.