Myosin Light Chain Kinase 4 (MYLK4)

MYLK4 is a member of the myosin light-chain kinase family of serine/threonine-specific protein kinases that phosphorylate the regulatory light chain of myosin II.

These enzymes are important in the mechanism of contraction in muscle. Once there is an influx of calcium cations (Ca⁺⁺) into the muscle, either from the sarcoplasmic reticulum or, more importantly, from the extracellular space, contraction of smooth muscle fibers may begin. First, the calcium will bind to calmodulin.This binding will activate MLCK, which will go on to phosphorylate the myosin light chain at serine residue 19. This will enable the myosin crossbridge to bind to the actin filament and allow contraction to begin (through the crossbridge cycle).