Phosphorylation of myosin light chain kinase by p21-activated kinase PAK2

J Biol Chem. 2000 Jun 16;275(24):18366-74. doi: 10.1074/jbc.M001339200.


Phosphorylation of myosin II regulatory light chains (RLC) by Ca(2+)/calmodulin-dependent myosin light chain kinase (MLCK) is a critical step in the initiation of smooth muscle and non-muscle cell contraction. Post-translational modifications to MLCK down-regulate enzyme activity, suppressing RLC phosphorylation, myosin II activation, and tension development. Here we report that PAK2, a member of the Rho family of GTPase-dependent kinases, regulates isometric tension development and myosin II RLC phosphorylation in saponin permeabilized endothelial monolayers. PAK2 blunts tension development by 75% while inhibiting diphosphorylation of myosin II RLC. Cdc42-activated placenta and recombinant, constitutively active PAK2 phosphorylate MLCK in vitro with a stoichiometry of 1.71 +/- 0. 21 mol of PO(4)/mol of MLCK. This phosphorylation inhibits MLCK phosphorylation of myosin II RLC. PAK2 catalyzes MLCK phosphorylation on serine residues 439 and 991. Binding calmodulin to MLCK blocks phosphorylation of Ser-991 by PAK2. These results demonstrate that PAK2 can directly phosphorylate MLCK, inhibiting its activity and limiting the development of isometric tension.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Calcium / metabolism
  • Calmodulin / metabolism
  • Electrophoresis, Polyacrylamide Gel
  • Endothelium / enzymology
  • HeLa Cells
  • Humans
  • Mutagenesis, Site-Directed
  • Myosin-Light-Chain Kinase / metabolism*
  • Peptide Mapping
  • Phosphorylation
  • Protein-Serine-Threonine Kinases / metabolism*
  • p21-Activated Kinases


  • Calmodulin
  • PAK2 protein, human
  • Protein-Serine-Threonine Kinases
  • p21-Activated Kinases
  • Myosin-Light-Chain Kinase
  • Calcium