Myosin

Myosins are mechanoenzymes that interact with actin filaments and hydrolyse ATP to generate movement and force. This enables myosins to propel the sliding of actin filaments, to produce tension on actin filaments and to walk along these filaments. As a result, myosins can regulate the structure and dynamics of the actin cytoskeleton and affect the localization and transport of cellular components. The different myosins are grouped into classes on the basis of their motor domains. There are 35 known classes of myosin, and humans have 40 myosin genes that fall into 13 classes (I, II, III, V, VI, VII, IX, X, XV, XVI, XVIII, XIX and XXXV).

Myosins are actin-dependent motors that participate in a diverse range of crucial activities, including muscle contraction, intracellular trafficking, cell division, motility, actin cytoskeletal organisation and cell signaling. Myosin malfunction has been implicated in a variety of disorders including deafness, hypertrophic cardiomyopathy, Usher syndrome, Griscelli syndrome and cancer.

Myosin light chain kinase (MLCK) is an enzyme that activates the myosin light chain to exert its function related to cytoskeleton contraction and tight junction regulation. In most cells, MLCK is a transducer for signalling MLC phosphorylation in response to Ca²⁺ binding to MLCK-associated calmodulin. MLCK-mediated MLC phosphorylation and actomyosin contractility is important in muscle contraction, cell migration, and endo/exocytic processes, and is recognized for its central role in signalling endothelial cell-cell adhesion and barrier function.