2 NOVEL TESTICULAR SERINE PROTEASES, TESP1 AND TESP2, ARE PRESENT IN THE MOUSE SPERM ACROSOME

To identify a novel candidate(s) for acrosomal proteins that act on th e sperm/egg interaction, a DNA fragment was PCR-amplified from a cDNA library of acrosin-deficient mouse testis and then used as a probe to screen a mouse testis cDNA library. Complementary DNA clones encoding each of two similar but different serine proteases, TESP1 and TESP2, h ave been identified. The nucleotide sequences of these clones indicate that mouse TESP1 and TESP2 are initially synthesized as preproprotein s of 367 and 366 amino acids, respectively. Comparison of the two TESP sequences with those of typical serine proteases suggests that each T ESP zymogen is probably converted into a two-chain mature enzyme consi sting of light and heavy chains covalently linked by a single pre-exis ting disulfide bond. The conversion may be accomplished by another pro tease(s) with a trypsin-like cleavage specificity, since it is unlikel y that the mature TESP1 and TESP2 are capable of splitting the Lys-Ile bond between the light and heavy chains. Northern blot analysis of to tal cellular RNA demonstrates that the TESP1 and TESP2 genes are expre ssed only in the testis, and the transcripts are abundantly present in the haploid round spermatids. Moreover, immunocytochemical analysis o f mouse cauda epididymal sperm using affinity-purified antibodies reve als that these two TESPs are both localized in the sperm acrosome and are released during the acrosome reaction induced by calcium ionophore A23187. These findings provide additional clues for elucidating the m echanisms involved in the sperm/egg interactions, including penetratio n of the zona pellucida by sperm. (C) 1998 Academic Press.