dictyNews
Electronic Edition
Volume 35, number 14
Nov 19, 2010
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Abstracts
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Autophosphorylation activates Dictyostelium Myosin II Heavy Chain Kinase A
by providing a ligand for an allosteric binding site in the alpha-kinase domain
Scott W. Crawley1, Mojdeh Samimi Gharaei 1, Qilu Ye1, Yidai Yang1,
Barak Raveh2, Nir London2, Ora Schueler-Furman2, Zongchao Jia1
and Graham P. Côté1
1Department of Biochemistry, Queen’s University, Kingston, Ontario,
Canada K7L 3N6
2Department of Microbiology and Molecular Genetics, Institute for Medical
Research Israel-Canada, Hadassah Medical School, The Hebrew University,
Jerusalem, 91120 Israel
The Journal of Biological Chemistry, in press
Dictyostelium discoideum myosin II heavy chain kinase A (MHCK A), a member
of the atypical alpha-kinase family, phosphorylates sites in the myosin II tail that
block filament assembly. Here we show that the catalytic activity of A-CAT, the
alpha-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 Thr825, which was found to be
constitutively autophosphorylated. Dephosphorylation of Thr825 using shrimp
alkaline phosphatase decreased A-CAT activity. The activity of a truncated
ACAT lacking Thr825 could be rescued by Pi, phosphothreonine and a
phosphorylated peptide, but not by threonine, glutamic acid, aspartic acid or
an unphosphorylated peptide. These results focused attention on a Pi-binding
pocket located in the C-terminal lobe of ACAT. Mutational analysis
demonstrated that the Pi-pocket was essential for A-CAT activity. Based on
these results, it is proposed that autophosphorylation of Thr825 activates
ACAT by providing a covalently-tethered ligand for the Pi-pocket. Ab initio
modeling studies using the Rosetta FloppyTail and FlexPepDock protocols
showed that it is feasible for the phosphorylated Thr825 to dock intramolecularly
into the Pi-pocket. Allosteric activation is predicted to involve a conformational
change in Arg734, which bridges the bound Pi to Asp762 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.
Submitted by Scott Crawley [[log in to unmask]]
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