Purification and identification of sperm surface proteins and changes during epididymal maturation

Surface membrane proteins have a key role in the sequential interactions between spermatozoa and oocytes. The aim of this study was to characterize protein changes occurring during post-testicular differentiation using a new overall approach to study surface membrane proteins of spermatozoa. A dedicated protocol based on specific purification of surface membrane proteins labeled with sulfo-NHS-SS-biotin was developed for this purpose. Appropriate gel electrophoresis separation and purification methods combined with standard proteomic methods were then used to identify and quantify surface membrane proteins from immature and mature spermatozoa. Membrane-associated proteins were discriminated from integral membrane proteins by differential solubilization. Protein regionalization on the spermatozoon surface was achieved by comparative analysis of the surface protein extracts from the entire spermatozoa and from periacrosomal sperm plasma membranes. Identification of several known proteins and of new proteins related to the process of epididymal maturation showed the reliability of this protocol for specific purification of a subproteome and identification of new sperm membrane proteins. This approach opens up a new area in the search for male fertility markers.