Postacrosomal Sheath WW Domain Binding Protein (PAWP)

WBP2NL is a sperm-specific WW domain-binding protein that promotes meiotic resumption and pronuclear development during oocyte fertilization. The predicted 309-amino acid human protein contains an N-terminal region homologous to WW domain-binding protein-2 (WBP2) and a proline-rich C-terminal half with a PPxY motif and 9 YGxPPxG repeats. Northern blot analysis detected a predominant 1.6-kb transcript and a less abundant 2-kb transcript in human testis. Western blot analysis showed a 32-kD protein in human testis. Immunostaining of bull testis showed that Pawp was expressed solely in elongating spermatids, and Pawp localized to the postacrosomal sheath region of the perinuclear theca of mature spermatozoa of various species, including monkey, bull, and pig.