A complex between the calcium-(Ca2+) bound protein calmodulin with a 26 amino acid residue long synthetic peptide representing the CaM domain (res. 577 to 602) of rabbit skeletal mucle myosin light chain kinase is shown here. Calmodulin controls a vast number of enzymes via calcium, a second messenger. When calmodulin binds to calcium, the enzymes most likely to be stimulated are protein kinases and phosphatases. Rabbit skeletal muscle myosin light chain kinase, or Mlck, phosphorylates a specific serine residue in the N-terminus of a myosin light chain. Catalytically, this enzyme performs the following reaction: ATP + [myosin light-chain] = ADP + [myosin light-chain] phosphate.
The overall conformation of the complex is globular. The helical peptide passes through the center of calmodulin via a hydrophobic channel. Calmodulin is 148 amino acid residues long, and is shown bound to 4 calcium ions (gold). The peptide residues from right to left are as follows: Lys-Arg-Arg-Trp-Lys-Asn-Phe-Ile-Ala-Val-Ser-Ala-Ala-Asn-Arg-Phe-Lys-Lys-Ile-Ser-Ser Ser-Gly-Ala-Leu.