Fig. 1

The general structure of S100 proteins. A Apo-S100 protein shown with a purple subunit and a yellow subunit. S100 proteins are regulated by Ca²⁺ binding (red circles), which allows them to function as Ca²⁺ sensors that can convert changes in intracellular Ca²⁺ levels into a cellular response. Ca²⁺ binding induces a conformational rearrangement that exposes a hydrophobic cleft, which is necessary for the S100 protein to bind its cellular targets (green) and elicit a physiological response. B The mode of S100A1 action demonstrates the calcium-dependent conformational change that is helpful for S100A1 to interact with its target molecules