Calmodulin EF Hand

Here is the structure of amino acids 118-148 of human calmodulin. This proteins binds calcium and modulates many intracelluar processes - it is a calcium modulatory protein (or calmodulin). Shown is a helix-loop-helix supersecondary structure motiff. Calcium (shown in spacefill rendering) is bound in the loop and is coordinated to Glu side chains protruding in from the loop