Genetic mapping of antigenic determinants on a membrane protein

The antigenic determinants recognized by two monoclonal antibodies were mapped on LamB, an outer membrane protein of Escherichia coli. The procedure consisted of performing immunoprecipitation experiments with extracts of strains which produced truncated fragments of LamB, either in a free form (deletion and nonsense mutants) or fused to another polypeptide (malK-lamB and lamB-lacZ fusion strains). The conclusion is that the two antigenic determinants are located within 70 residues from the COOH-terminal end of LamB, which contains a total of 421 amino acids. Since these two antigenic sites were previously demonstrated to be exposed at the cell surface, it follows that a COOH-terminal portion of LamB must be located on the outer surface of the outer membrane.