Myosin light-chain kinase

Jump to: navigation, search

Template:Infobox protein Template:Infobox protein Template:Infobox protein Template:Infobox protein Myosin light-chain kinase also known as MYLK or MLCK is a serine/threonine-specific protein kinase that phosphorylates a specific myosin light chain, namely, the regulatory light chain of myosin II.[1]


Four different MLCK isoforms exist:[2]


These enzymes are important in the mechanism of contraction in muscle. Once there is an influx of calcium cations (Ca2+) into the muscle, either from the sarcoplasmic reticulum or from the extracellular space, contraction of smooth muscle fibres 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). Since smooth muscle does not contain a troponin complex, as striated muscle does, this mechanism is the main pathway for regulating smooth muscle contraction. Reducing intracellular calcium concentration inactivates MLCK but does not stop smooth muscle contraction since the myosin light chain has been physically modified through phosphorylation(and not via ATPase activity). To stop smooth muscle contraction this change needs to be reversed. Dephosphorylation of the myosin light chain (and subsequent termination of muscle contraction) occurs through activity of a second enzyme known as myosin light-chain phosphatase (MLCP).

See also


  1. Gao Y, Ye LH, Kishi H, Okagaki T, Samizo K, Nakamura A, Kohama K (June 2001). "Myosin light chain kinase as a multifunctional regulatory protein of smooth muscle contraction". IUBMB Life. 51 (6): 337–44. PMID 11758800. doi:10.1080/152165401753366087. 
  2. Manning G, Whyte DB, Martinez R, Hunter T, Sudarsanam S (December 2002). "The protein kinase complement of the human genome". Science. 298 (5600): 1912–34. PMID 12471243. doi:10.1126/science.1075762. 

Further reading


External links

This article incorporates text from the United States National Library of Medicine, which is in the public domain.

Template:Portal bar