150. THE CAPACITATION INDUCED FORMATION OF A MULTIMERIC SPERM - ZONA PELLUCIDA RECEPTOR COMPLEX

Abstract

The ability of mammalian spermatozoa to fertilize the oocyte is dependent on a complex cascade of biophysical and biochemical changes collectively known as capacitation. This final phase of sperm maturation is characterised by a dramatic remodelling of the sperm surface architecture to render the cell competent to recognise and bind to the zona pellucida. Although the current paradigm suggests this interaction is mediated by a single receptor-ligand interaction, recent evidence emerging from our laboratory suggests that this event is more complex and involves the capacitation-dependent formation of a multimeric zona pellucida receptor complex. Through the novel application of Blue Native PAGE and Far Western blotting, we have recently identified the first such complex that displays the anticipated affinity for the zona pellucida. LCMS analysis revealed that this high molecular weight complex is comprised of a family of 8 chaperonin subunits that form an active t-complex polypeptide-1 (TCP-1) complex. In addition, this complex was also shown to contain an N-acetylglucosaminyltransferase, GCnT2, an enzyme with affinity for N-acetylglucosamine. Importantly, this sugar forms part of the zona pellucida glyco-matrix and has previously been implicated as a ligand for sperm interaction. Consistent with this notion, incubation of sperm with anti-GCnT2 antibodies or N-acetylglucosamine competitively inhibited sperm-zona pellucida interactions in a dose dependent manner. Collectively, this data raises the intriguing possibility that chaperonin proteins participate in the assembly and/or presentation of key zona adhesion molecules during capacitation. Future work is aimed at identifying additional zona receptors that may reside within this complex.