Component of the sperm acrosome membrane (PubMed:17092953). Required for breakdown of the sperm plasma membrane after sperm entry into the egg, which is an essential prerequisite for successful fertilization (PubMed:9630751, PubMed:17092953). Has diffuse cytoplasmic expression in primary spermatocytes. In post-meiotic spermatids, detected in clusters of vesicle-like structures adjacent to the nucleus. In late spermatids, a single vesicle-like spot is found near the nucleus, which probably corresponds to the acroblast. In mature sperm, localizes to the apical tip of the sperm head (acrosome). Specifically expressed in testis.