Calcium-induced environmental adaptability of the blood protein vitronectin.

The adaptability of proteins to their work environments is fundamental for cellular life. Here, we describe how the hemopexin-like domain of the multifunctional blood glycoprotein vitronectin binds Ca to adapt to excursions of temperature and shear stress. Using X-ray crystallography, molecular dynamics simulations, NMR, and differential scanning fluorimetry, we describe how Ca and its flexible hydration shell enable the protein to perform conformational changes that relay beyond the calcium-binding site and alter the number of polar contacts to enhance conformational stability. By means of mutagenesis, we identify key residues that cooperate with Ca to promote protein stability, and we show that calcium association confers protection against shear stress, a property that is advantageous for proteins that circulate in the vasculature, like vitronectin.