Myosin light chain kinases

Ca²⁺ is a second messenger that activates many Ca²⁺-dependent cellular processes. Ca²⁺ has been recognized as an important component in muscle contraction and cell motility because it regulates a distinct class of protein kinases, myosin light chain kinases.^1-3 Activation of myosin light chain kinase by Ca²⁺/calmodulin results in phosphorylation of a regulatory light chain subunit of myosin. Myosin light chain phosphorylation leads to potentiation of contraction in striated muscles, but initiates contraction in smooth muscles. Before reviewing the catalytic properties of myosin light chain kinases, a general discussion of contractile proteins and the role of myosin phosphorylation will be presented so that the reader will have some appreciation of the biological importance of this class of kinases. The main topic, however, will deal with their respective biochemical properties as elucidated with peptides.