178. THE CHAPERONIN CONTAINING TCP-1 (CCT/TRiC) MULTISUBUNIT COMPLEX IS INVOLVED IN MEDIATING SPERM–OOCYTE INTERACTIONS

Abstract

Mammalian spermatozoa only express their capacity for fertilization following capacitation, a process characterized by a suite of biophysical and biochemical changes that occurs as the cells ascend the female reproductive tract. A key event associated with the attainment of a capacitated state is a dramatic reorganization of the sperm surface architecture to render these cells competent to bind to the protective matrix of the oocyte, the zona pellucida. Our previous analysis of these remodeling events has provided compelling evidence that they include the assembly and/or presentation of multimeric protein complexes on the sperm surface. In addition, we have demonstrated that at least two of these complexes possess strong affinity for solubilized zona pellucida. In our current study we have utilised mass spectrometry analysis to reveal that one of these complexes comprises the eight subunits that form a composite, multimeric structure known as the chaperonin containing TCP-1 (CCT/TRiC) complex. Our collective data suggest that this complex participates indirectly in zona pellucida interaction, possibly through the conveyance of key zona adhesion molecules to the sperm surface during capacitation. Consistent with this notion, we were able to demonstrate that the sperm CCT/TRiC complex releases its bound substrates upon exposure to ATP, and this treatment induced a significant, concomitant reduction in the ability of capacitated sperm to bind to the zona pellucida. Furthermore, the use of immunoprecipitation assays confirmed the interaction of the CCT/TRiC complex with at least one putative zona pellucida receptor candidate, namely zona pellucida binding protein 2 (ZPBP2). Future work is now aimed at identifying additional zona receptors that may reside within this complex and the pathways that regulate its functional assembly.