MYLK

MYLK refers to a gene family that encodes myosin light chain kinase (MLCK), a calcium/calmodulin-dependent serine/threonine kinase that phosphorylates the regulatory light chain of myosin II, enabling actomyosin contraction. In humans, the MYLK locus produces multiple kinase isoforms through alternative promoters and splicing, including long MLCK (MLCK-L) and nonmuscle MLCK (nmMLCK). A skeletal-muscle–specific member is encoded by the related MYLK2 gene; transcription from MYLK can also yield a smaller regulatory protein known as telokin in some tissues.

MLCK is activated by Ca2+-bound calmodulin. Once active, it phosphorylates the regulatory light chain of myosin II (MLC20) at Ser19, increasing myosin ATPase activity and promoting contraction. Its activity is opposed by myosin light chain phosphatase (MLCP), and cellular calcium signaling shifts the balance to regulate contractile tone and cytoskeletal remodeling.

Physiologically, MLCK drives smooth muscle contraction that controls vascular and airway tone, gastrointestinal motility, and other hollow-organ functions. In nonmuscle cells, MLCK participates in actomyosin-based processes such as cell migration, adhesion, cytokinesis, and maintenance of cell shape. Regulation is multifactorial, involving calcium signaling, calmodulin binding, phosphorylation, and interactions with signaling cascades.

Genetic and clinical relevance: variants in MYLK have been linked to familial thoracic aortic aneurysm and dissection in some families, illustrating a role in vascular integrity. Altered MLCK activity has also been studied in contexts of inflammation and epithelial barrier function. Overall, MYLK represents a conserved regulator of contraction and cytoskeletal dynamics across tissues.