Glycan-modifying enzymes in luminal fluid of the mammalian epididymis: An overview of their potential role in sperm maturation

Testicular spermatozoa and those present within the proximal regions of the epididymis are unable to bind to the zona pellucida, the extracellular coat that surrounds the oocyte, and fertilize the egg. They acquire progressive motility and fertilizing ability during passage through the epididymis. Mammalian spermatozoa undergo biochemical and physiological changes during epididymal transit that are collectively termed epididymal maturation. The process involves several intracellular and extracellular changes in the spermatozoon, including remodeling of the sperm plasma membrane and modifications of glycan moieties of the sperm surface glycoconjugates. Two sets of glycan-modifying enzymes, namely glycohydrolases that cleave sugar residues and glycosyltransferases that add sugar residues to the existing glycoconjugates, are present in the epididymal luminal fluid that surrounds spermatozoa. Thus, it is reasonable to expect that glycan chains present on the sperm surface will interact with these glycan-modifying enzymes in the epididymal fluid. In this article, I have attempted to summarize and present an overview on the potential role of these glycan-modifying enzymes in sperm maturation. (c) 2005 Elsevier Ireland Ltd. All rights reserved.