Myosin light-chain kinase

myosin light-polypeptide kinase, smooth muscle
Symbol MYLK
Entrez 4638
HUGO 7590
OMIM 600922
RefSeq NM_053025
UniProt Q15746
Other data
EC number
Locus Chr. 3 qcen-q21
myosin light-chain kinase 2, skeletal muscle
Crystal structure of the S. dubia centrin / human skeletal muscle myosin light-chain complex.[1]
Symbol MYLK2
Entrez 85366
HUGO 16243
OMIM 606566
RefSeq NM_033118
UniProt Q9H1R3
Other data
Locus Chr. 20 q13.31
myosin light-chain kinase 3, cardiac
Symbol MYLK3
Entrez 91807
HUGO 29826
OMIM 612147
RefSeq NM_182493
UniProt Q32MK0
Other data
Locus Chr. 16 q11.2
Human Myosin Light-Chain Kinase
The Crystal Structure of the Human Myosin Light Chain Kinase Loc340156.[2]
Symbol MYLK4
Entrez 340156
HUGO 27972
RefSeq NM_001012418
UniProt Q86YV6
Other data

Myosin light-chain kinase also known as MYLK or MLCK is a serine/threonine-specific protein kinase that phosphorylates the regulatory light chain of myosin II.[3]



Four different MLCK isoforms exist:[4]

  • MYLK – smooth muscle
  • MYLK2 – skeletal
  • MYLK3 – cardiac
  • MYLK4 – novel


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 important, 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. 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 MLCP (Myosin Light Chain Phosphatase).

See also


  1. ^ "RCSB Protein Data Bank - Structure Summary for 3KF9 - Crystal structure of the SdCen/skMLCK complex". 
  2. ^ "RCSB Protein Data Bank - Structure Summary for 2X4F - The Crystal Structure of the Human Myosin Light Chain Kinase Loc340156.". 
  3. ^ 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. doi:10.1080/152165401753366087. PMID 11758800. 
  4. ^ 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. doi:10.1126/science.1075762. PMID 12471243. 

Further reading

External links

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