Calcium-binding protein. Molecular model showing the alpha-helical secondary structure of the calcium-binding protein calmodulin (CaM). This molecule has four calcium ions (orange) bound to it, the maximum number a single molecule can bind. This protein is found in all eukaryotic cells, where it regulates and modifies the activities of many calcium-binding enzymes. Cellular processes that CaM affects include muscle contraction, inflammation, immune response and memory.