Regulatory Mechanism of Dictyostelium Myosin Light Chain Kinase A

Hiroshi Tokumitsu*, Naoya Hatano, Hiroyuki Inuzuka, Yumi Ishikawa, Taro Q.P. Uyeda, Janet L. Smith, Ryoji Kobayashi

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

5 Citations (Scopus)


In this study, we examined the activation mechanism of Dictyostelium myosin light chain kinase A (MLCK-A) using constitutively active Ca 2+/calmodulin-dependent protein kinase kinase as a surrogate MLCK-A kinase. MLCK-A was phosphorylated at Thr166 by constitutively active Ca2+/calmodulin-dependent protein kinase kinase, resulting in an ∼140-fold increase in catalytic activity, using intact Dictyostelium myosin II. Recombinant Dictyostelium myosin II regulatory light chain and Kemptamide were also readily phosphorylated by activated MLCK-A. Mass spectrometry analysis revealed that MLCK-A expressed by Escherichia coli was autophosphorylated at Thr289 and that, subsequent to Thr 166 phosphorylation, MLCK-A also underwent a slow rate of autophosphorylation at multiple Ser residues. Using site-directed mutagenesis, we show that autophosphorylation at Thr289 is required for efficient phosphorylation and activation by an upstream kinase. By performing enzyme kinetics analysis on a series of MLCK-A truncation mutants, we found that residues 283-288 function as an autoinhibitory domain and that autoinhibition is fully relieved by Thr166 phosphorylation. Simple removal of this region resulted in a significant increase in the kcat of MLCK-A; however, it did not generate maximum enzymatic activity. Together with the results of our kinetic analysis of the enzymes, these findings demonstrate that Thr166 phosphorylation of MLCK-A by an upstream kinase subsequent to autophosphorylation at Thr289 results in generation of maximum MLCK-A activity through both release of an autoinhibitory domain from its catalytic core and a further increase (15-19-fold) in the kcat of the enzyme.

Original languageEnglish
Pages (from-to)42-50
Number of pages9
JournalJournal of Biological Chemistry
Issue number1
Publication statusPublished - 2004 Jan 2
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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