Amino acid sequences of porcine Sp38 and proacrosin required for binding to the zona pellucida.

We previously purified a boar sperm protein, sp38, and demonstrated that this protein bound to the 90-kDa family of zona pellucida (ZP) glycoprotein in a calcium-dependent manner. Sp38 competed with proacrosin for the binding to the zona pellucida. Herein we have isolated cDNA clones encoding sp38 from a boar testis cDNA library in lambda gt11. The amino acid sequence deduced from the cDNA sequence indicated that sp38 is initially synthesized as a 350-residue precursor protein. The N-terminal 51-residue sequence preceded the N-terminus of the mature sp38. Thus, the sp38 precursor is post-translationally modified to produce the mature protein of 299 residues. Immunostaining of sperm cells using an antibody prepared against a fusion protein of sp38 with T7 gene 10 protein suggested that sp38 is localized at the intraacrosomal region and is released after the acrosome reaction. The 11-residue sequence, KRLSKAKNLIE, in sp38 shared a significant degree of similarity with the 8-residue sequence, KRLQQLIE, in the C-terminal region of porcine proacrosin. Both synthetic oligopeptides corresponding to these two sequences inhibited the binding of 125I-labeled sp38 to zona pellucida glycoprotein.