Isolation of major proteins from boar sperm plasma membranes by preparative gel electrophoresis and localization of a major polypeptide using specific monoclonal antibodies.

A preparative procedure using two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) is described for isolating major boar sperm plasma membrane polypeptides (PMPs) in soluble form. Proteins were first separated on 6 mm diameter gels using a pH gradient expanded in the acidic region. The second dimension used 6 mm thick, 10% acrylamide gels. Major proteins identified by Coomassie staining were excised and electroeluted. The procedure was applied to the isolation of a group of proteins in the molecular weight range 40K-50K which comprise a major fraction of the total integral membrane protein in these cells (groups 4 and 5). Yields of electrophoretically pure soluble polypeptides from these groups were between 0.3 mg - 0.5 mg from the processing of 16 gels per week. Electroeluted proteins were also used to elicit monoclonal antibodies to major proteins. Monoclonal antibodies to the major plasma membrane protein referenced as 4.85 were isolated and shown to be specific to this protein by transblotting procedures. This protein was primarily localized over the anterior portion of the principal segment of ejaculated sperm by indirect FITC fluorescence microscopy. The ability to isolate 60-100 mg of plasma membranes per week from the cauda epididymides of boars also permitted developing a procedure for the rapid fractionation of large amounts of detergent solubilized plasma membranes by isoelectric focusing in flatbeds of Biogel P200. For the first time, individual proteins of sperm surface proteins can be isolated in large enough amounts to begin detailed biochemical characterization, localization, and functional testing.