Autophosphorylation activates Dictyostelium myosin II heavy chain kinase A by providing a ligand for an allosteric binding site in the alpha-kinase domain

J Biol Chem. 2011 Jan 28;286(4):2607-16. doi: 10.1074/jbc.M110.177014. Epub 2010 Nov 11.

Abstract

Dictyostelium discoideum myosin II heavy chain kinase A (MHCK A), a member of the atypical α-kinase family, phosphorylates sites in the myosin II tail that block filament assembly. Here we show that the catalytic activity of A-CAT, the α-kinase domain of MHCK A (residues 552-841), is severely inhibited by the removal of a disordered C-terminal tail sequence (C-tail; residues 806-841). The key residue in the C-tail was identified as Thr(825), which was found to be constitutively autophosphorylated. Dephosphorylation of Thr(825) using shrimp alkaline phosphatase decreased A-CAT activity. The activity of a truncated A-CAT lacking Thr(825) could be rescued by P(i), phosphothreonine, and a phosphorylated peptide, but not by threonine, glutamic acid, aspartic acid, or an unphosphorylated peptide. These results focused attention on a P(i)-binding pocket located in the C-terminal lobe of A-CAT. Mutational analysis demonstrated that the P(i)-pocket was essential for A-CAT activity. Based on these results, it is proposed that autophosphorylation of Thr(825) activates ACAT by providing a covalently tethered ligand for the P(i)-pocket. Ab initio modeling studies using the Rosetta FloppyTail and FlexPepDock protocols showed that it is feasible for the phosphorylated Thr(825) to dock intramolecularly into the P(i)-pocket. Allosteric activation is predicted to involve a conformational change in Arg(734), which bridges the bound P(i) to Asp(762) in a key active site loop. Sequence alignments indicate that a comparable regulatory mechanism is likely to be conserved in Dictyostelium MHCK B-D and metazoan eukaryotic elongation factor-2 kinases.

Publication types

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

MeSH terms

  • Calcium-Calmodulin-Dependent Protein Kinases / genetics
  • Calcium-Calmodulin-Dependent Protein Kinases / metabolism*
  • Dictyostelium / enzymology*
  • Dictyostelium / genetics
  • Enzyme Activation / physiology
  • Mutation
  • Phosphorylation / physiology
  • Protein Structure, Tertiary
  • Protozoan Proteins / genetics
  • Protozoan Proteins / metabolism*

Substances

  • Protozoan Proteins
  • Calcium-Calmodulin-Dependent Protein Kinases
  • myosin-heavy-chain kinase

Associated data

  • PDB/3PDT