Acrosomal membrane-anchored protein involved in the process of fertilization and in acrosome biogenesis. Interacts with SNAP25. In the anterior acrosome region, enriched on the inner acrosomal membrane but minimal on the outer acrosomal membrane; in contrast in the posterior acrosome region enriched on both the inner and outer acrosomal membranes. Isoform 1 is highly expressed in testis. Isoform 2 is expressed at low levels in skin and blood. Highly N- and O-glycosylated; contains sialic acid.