Structural changes in myosin subfragment 1 by mild denaturation and proteolysis probed by antibodies

The perturbations in the structure of myosin subfragment 1 (S1) by mild denaturation or proteolysis were investigated by measuring the inhibition of the binding of antibodies to immobilized S1 by treated S1 in a solution-phase competitive immunochemical assay. The structural changes in S1 were probed by using anti-50-kDa segment, anti-N-terminus, anti-27-kDa segment, and anti-A1 light chain monoclonal antibodies (MAbs). Methanol and heat denaturation increased MAb binding to the 50-kDa segment. MAb binding to regions in the 27-kDa segment was also promoted, slightly by methanol and more drastically by heat. Proteolysis also induced structural alterations in 50- and 27-kDa segments as shown by increased MAb binding to these regions in cleaved S1. These results indicate that mild denaturation and proteolysis induce structural perturbations which alter the epitope accessibility in 50- and 27-kDa segments of S1 and that antibody binding studies afford a sensitive probe to such perturbations.