In the picture above, the two key residues are in red, M13 in green and calmodulin in blue. Biology Myosin Myosin is an important motor molecule in muscle cells. Its activity requires actin. Myosin is composed of the heavy chain and the light chain. Heavy chain contains ATPase domain which hydrolyses ATP and use the energy to change the conformation and generate force.
Light chain is at the neck region of myosin, and often is used as a regulatory domain.
In vertebrates, phosphorylation of myosin light chain activates myosin. M13 M13 is a synthetic peptide. It was used to demonstrate that calmodulin can bind the peptide without the presence of the entire protein. Calmodulin Calmodulin is a ubiquitous protein that regulates many cellular processes by monitoring the calcium level in a cell. Calmodulin, normally present in the cytoplasm, binds calcium ions and changes conformation.