Glycosyl Phosphatidyl Inositol (GPI) Anchored Molecules on Mammalian Spermatozoa

Abstract

Sperm cells, like somatic cells, are surrounded by a plasma membrane that participates in early events of fertilization including capacitation, sperm-egg interaction and the acrosome reaction. Thus, an understanding of the composition and organization of sperm membrane is important to ascertain its role in the fertilization process. The sperm plasma membrane is predominantly composed of phospholipids and cholesterol. A change in the relative concentrations of these two components determines the permeability, fluidity, rigidity and functional state of the gamete. A mosaic of other molecules including proteins is scattered and embedded in this structure (1). Spermatozoa require a large number of proteins to become competent and fertilize the egg. Unfortunately, the cells have no known synthetic activity and the number of molecules that can be physically accommodated at any given time is severely restricted by their miniscule size. One strategy by which spermatozoon overcomes this limitation is to choose a type of anchorage/mechanism that economizes on the number of surface molecules.