Developing spermatozoa need a series of post-testicular modifications within the luminal environment of the epididymis to achieve maturation; this involves several surface modifications VER 155008 including changes in plasma membrane lipids proteins carbohydrates and alterations in the outer acrosomal membrane. the cauda sperm plasma membrane not in the caput sperm plasma membrane. Among the several WGA stained bands the presence of a 17.5kDa WGA binding polypeptide band was detected only in cauda epididymal fluid not in caput epididymal fluid suggesting that the 17.5kDa WGA-binding polypeptide is secreted from the cauda epididymis and binds to the cauda sperm plasma membrane during epididymal transit. Proteomic identification of the 17.5kDa polypeptide yielded 13 peptides that matched the sequence of peroxiredoxin-5 (PRDX5) protein (Bos Taurus). We propose that bovine cauda sperm PRDX5 acts as an antioxidant enzyme in the epididymal environment which HDAC9 is crucial in protecting the viable sperm population against the damage caused by endogeneous or exogeneous peroxide. Keywords: Bovine sperm Epididymis Glycoproteins Peroxiredoxin-5 INTRODUCTION Fertilization the union of male and female gametes to create offspring is an intricate biological process dependent upon several biochemical and physiological events [1 2 Spermatozoa leave the testis as morphologically differentiated and functionally immature cells and require a series VER 155008 of post-testicular modifications to become fertilizing competent [3 4 The mammalian epididymis represents the site where incompetent testicular sperm undergo maturation and is comprised of three distinct regions: the VER 155008 caput corpus and cauda [1 5 6 As sperm cells travel through the duct they become mature acquiring forward motility and the capability to fertilize the ovum [7-11]. During the maturational process plasma membrane proteins undergo several compositional changes via the addition of new components to the sperm surface the unmasking or modification of preexisting sperm-surface moieties by protein redistribution between domains or the increased loss of sperm-surface parts [6 9 12 This membrane reorganization shows up crucial to the introduction of sperm practical capability. The maturational adjustments sperm undergo because they travel through the epididymis outcomes from the secretions of many proteins along the epididymal epithelium [6 13 as well as the pattern from the region-specific gene expression in the epididymis . Several studies reveal that the mammalian sperm plasma membrane surface is coated with various glycoproteins [15-18]. Sperm surface glycoproteins are thought to induce sperm maturation and fertilizing capacity in the epididymis [17 19 20 The extent to which these surface VER 155008 glycoproteins are altered varies from species to species and differs in each epididymal region . The plasma membrane is a mosaic of distinct domains corresponding to defined segments of the head and flagellum . In rat sperm plasma membrane several different glycoprotein alterations occur during post-testicular maturation including modifications in their appearance loss or alteration in staining intensity and modification of VER 155008 electrophoretic mobility . The mechanisms utilized by sperm to undergo the maturational process are still not completely understood however the epididymis does provide sperm with an environment essential for the acquisition of motility and fertilizing ability . Lectins are a class of proteins that can be used to analyze density and distribution variations of exposed saccharides in the sperm’s plasma membrane [17 23 Both lectin-like and protein-protein interactions exhibit a potential role in human sperm-egg interactions . The objective of the present study was VER 155008 to identify the maturation-dependent plasma membrane proteins of the bovine sperm and to elucidate their role with the production of functionally competent spermatozoa. Western Blots of SDS-PAGE fractionated bovine sperm plasma membrane samples identified a 17.5kDa WGA binding polypeptide present in the cauda sperm plasma membrane. Proteomic identification of the 17.5kDa polypeptide yielded 13 peptides that matched the sequence of peroxiredoxin-5(PRDX5) protein (BosTaurus). We propose that bovine cauda sperm PRDX5 acts as an antioxidant enzyme in the cauda epididymal environment to protect the viable sperm population against the damage caused by endogeneous or exogeneous peroxide. MATERIALS AND.