A monoclonal antibody that recognizes different conformational states of skeletal muscle troponin C and other calcium binding proteins.

Skeletal muscle troponin C contains four Ca(2+)-binding sites, two with a high affinity for Ca2+ that also bind Mg2+ competitively (Ca2+/Mg2+ sites) and two sites of lower affinity that are specific for Ca2+. We have characterized a monoclonal antibody (B9D9) that was produced against rabbit skeletal troponin C. The binding of this antibody to rabbit skeletal troponin C is sensitive to the binding of Ca2+. Increasing the Ca2+ concentration produces a decrease in the amount of antibody bound with a pK of approximately 6.9 which correlates with Ca2+ binding to the Ca2+/Mg2+ sites. Magnesium binding to rabbit skeletal troponin C had no effect on antibody binding. Thus the conformation of rabbit skeletal troponin C brought about by Ca2+ binding to these sites affects the antibody binding to its epitope. This epitope was unavailable for antibody binding in whole troponin. The antibody-binding site was localized in cyanogen bromide fragment CB9 of rabbit skeletal troponin C (residues 84-135). This antibody was also shown to cross-react with bovine cardiac troponin C, barnacle (Balanus nubilus) troponin C, bovine testis calmodulin and carp parvalbumin. In addition, the effect of Ca2+ on antibody binding seen with rabbit skeletal troponin C was also seen with bovine cardiac troponin C, and calmodulin. Thus these proteins appear to share a similar epitope and undergo similar structural changes. Wang and colleagues (1987) have presented evidence that rabbit skeletal troponin C at low pH has an elongated structure similar to that seen in the crystal structure and that at neutral pH its structure is more compact.(ABSTRACT TRUNCATED AT 250 WORDS)