Conformational regulation of the C-terminal random coil in S100A4 by Ca2+ ions

S100A4 or metastasin plays a central role in the progression of metastatic diseases. Like many other examples, the protein S100A4 contains ordered and disordered regions. The aim of this study was to determine how the disordered C-terminal region influences the binding to Ca2+ and in turn how Ca2+ binding alters the dynamics of the C-terminal random coil. The combination of small angle X-ray scattering, pulsed field gradient NMR measurements revealed a conformational change upon binding in the wild-type protein, but not in the C-terminal deleted mutant. Comparative isothermal titration calorimetry measurements also indicated that Ca2+ ions bind more tightly to the C-terminal deleted mutant than the wild-type protein. Molecular dynamics simulations provide a rational: in the wild type protein the positively charged C-terminal random coil region interacts strongly with the EF hand residues when they do not coordinate Ca2+ , whereas the C-terminal region is more free to move in the Ca2+-bound form of the pro...