Proteomic and functional analysis of human sperm detergent resistant membranes

Mammalian spermatozoa attain the ability to fertilize an oocyte as they negotiate the female reproductive tract. This acquisition of functional competence is preceded by an intricate cascade of biochemical and functional changes collectively known as "capacitation." Among the universal correlates of the capacitation process is a remarkable remodeling of the lipid and protein architecture of the sperm plasma membrane. While the mechanisms that underpin this dynamic reorganization remain enigmatic, emerging evidence has raised the prospect that it may be coordinated, in part, by specialized membrane microdomains, or rafts. In the present study we have demonstrated that human spermatozoa express recognized markers of membrane rafts. Further, upon depletion of membrane cholesterol through either physiological (capacitation) or pharmacological (methyl-β-cyclodextrin) intervention, these membrane rafts appear to undergo a polarized redistribution to the peri-acrosomal region of the sperm head. This finding encourages speculation that membrane rafts represent platforms for the organization of proteins involved in sperm-oocyte interactions. Support for this notion rests with the demonstration that membrane rafts isolated on the basis of their biochemical composition in the form of detergent resistant membranes (DRMs), possess the ability to adhere to homologous zona pellucidae. Furthermore a comprehensive proteomic analysis of the DRMs identified a number of proteins known for their affinity for the zona pellucida in addition to other candidates putatively involved in the mediation of downstream binding and/or fusion with the oolemma. Collectively these data afford novel insights into the subcellular localization and potential functions of membrane rafts in human spermatozoa.