Antigenicity and native structure of globular proteins: low frequency of peptide reactive antibodies

Recent reports that peptides can frequently mimic epitopes on globular proteins are inconsistent with early studies demonstrating that antibodies to native globular proteins generally do not bind peptides. This discrepancy could result from current confusion of two different populations of antibodies in antisera: one reacting with peptides and denatured protein and the other reacting only with the native protein. To test this possibility, several hundred monoclonal antibodies to rat cytochrome c were examined by ELISA for binding the intact protein and cyanogen bromide-cleaved peptides. Inhibition by soluble native cytochrome c identified which antibodies were specific for the native protein. The vast majority of these antibodies did not bind the peptides, whereas most of the antibodies specific for denatured forms did bind them. The results are consistent with the idea that antibodies to denatured antigen are readily detected in solid-phase assays, where some antigen molecules denature as they attach to microtiter plates, and show that these antibodies are generally the ones that react with peptides. Thus, reevaluation of data suggesting that anti-native globular protein antibodies bind peptides is warranted.