Myosin light chain kinase: Functional domains and structural motifs

James T. Stull, P. J. Lin, J. K. Krueger, J. Trewhella, G. Zhi

Research output: Contribution to journalArticlepeer-review

68 Scopus citations


Conventional myosin light chain kinase found in differentiated smooth and non-muscle cells is a dedicated Ca2+/calmodulin-dependent protein kinase which phosphorylates the regulatory light chain of myosin II. This phosphorylation increases the actin-activated myosin ATPase activity and is thought to play major roles in a number of biological processes, including smooth muscle contraction. The catalytic domain contains residues on its surface that bind a regulatory segment resulting in autoinhibition through an intrasteric mechanism. When Ca2+/calmodulin binds, there is a marked displacement of the regulatory segment from the catalytic cleft allowing phosphorylation of myosin regulatory light chain. Kinase activity depends upon Ca2+/calmodulin binding not only to the canonical calmodulin-binding sequence but also to additional interactions between Ca2+/calmodulin and the catalytic core. Previous biochemical evidence shows myosin light chain kinase binds tightly to actomyosin containing filaments. The kinase has low-affinity myosin and actin binding sites in Ig-like motifs at the N- and C-terminus, respectively. Recent results show the N-terminus of myosin light chain kinase is responsible for filament binding in vivo. However,the apparent binding affinity is greater for smooth muscle myofilaments, purified thin filaments, or actin-containing filaments in permeable cells than for purified smooth muscle F-actin or actomyosin filaments from skeletal muscle. These results suggest a protein on actin thin filaments that may facilitate kinase binding. Myosin light chain kinase does not dissociate from filaments in the presence of Ca2+/calmodulin raising the interesting question as to how the kinase phosphorylates myosin in thick filaments if it is bound to actin-containing thin filaments.

Original languageEnglish (US)
Pages (from-to)471-482
Number of pages12
JournalActa Physiologica Scandinavica
Issue number4
StatePublished - Jan 1 1998


  • Actin
  • Calcium
  • Calmodulin
  • Kinase
  • Myosin light chain kinase
  • Smooth muscle

ASJC Scopus subject areas

  • Physiology


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