A calcium- or manganese-dependent epitope on the integrin beta 1 chain recognized by a unique mAb

A calcium- or manganese-dependent epitope was demonstrated on the beta 1 integrin chain by a newly established mAb. In immunoprecipitation, the mAb was able to bind to the solubilized beta 1 integrin chain in the presence of calcium but not magnesium. Cation chelating reagents completely affected the binding of the antibody to the intact beta 1 integrin chain on a cell surface. Calcium but not magnesium restored the binding of the antibody. Quantitative analyses revealed that chelating reagents reduced the affinity of the antibody. Moreover, manganese also rescued epitope expression. These results suggested that divalent cations, particularly calcium or manganese, had a crucial role in the conformation of the beta 1 integrin chain recognized by the SG/7 antibody. This antibody would be of great use for studying the divalent cation-dependent modulation of the integrin molecules and bring another aspect to the understanding of the regulatory mechanisms of ligand binding of the integrin molecules.