dictyNews
Electronic Edition
Volume 34, number 8
March 5, 2010

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=========
Abstracts
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Crystal Structure of the Alpha-Kinase Domain of Dictyostelium Myosin 
Heavy Chain Kinase A

Qilu Ye*, Scott W. Crawley*, Yidai Yang, Graham P. Côté, and Zongchao Jia 

Department of Biochemistry, Queen’s University, Kingston, Ontario, 
Canada K7L 3N6. 

*These authors contributed equally to this work. 

To whom correspondence should be addressed. 
E-mail: coteg@queensu.ca 


Science Signaling, In press

Dictyostelium discoideum myosin II heavy chain kinase A (MHCK A) disrupts 
the assembly and cellular activity of bipolar filaments of myosin II by 
phosphorylating sites within its alpha-helical, coiled-coil tail. MHCK A is a 
member of the atypical alpha-kinase family of serine and threonine protein 
kinases and displays no sequence homology to typical eukaryotic protein 
kinases. We report the crystal structure of the alpha-kinase domain (A-CAT) 
of MHCK A. When crystallized in the presence of adenosine triphosphate 
(ATP), A-CAT contained adenosine monophosphate (AMP) at the active site. 
However, when crystallized in the presence of ATP and a peptide substrate, 
which does not appear in the structure, adenosine diphosphate (ADP) was 
found at the active site and an invariant aspartic acid residue (Asp766) at the 
active site was phosphorylated. The aspartylphosphate group was exposed to 
the solvent within an active-site pocket that might function as a docking site for 
substrates. Access to the aspartylphosphate was regulated by a conformational 
switch in a loop that bound to a magnesium ion (Mg2+), providing a mechanism 
that allows alpha-kinases to sense and respond to local changes in Mg2+. 


Submitted by Scott Crawley [crawleys@queensu.ca]
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A flavin-dependent halogenase catalyzes the
chlorination step in the biosynthesis of
Dictyostelium differentiation-inducing factor 1

Christopher S. Neumann (a), Christopher T. Walsh (a), and 
Robert R. Kay (b)

(a) Department of Biological Chemistry and Molecular Pharmacology, 
Harvard Medical School, 240 Longwood Avenue, Boston, MA 02115; 
and (b) Division of Cell Biology, Medical Research Council Laboratory 
of Molecular Biology, Hills Road, Cambridge CB2 OQH, UK


Proc Natl Acad Sci USA, in press

Differentiation-inducing factor 1 (DIF-1) is a polyketide-derived
morphogen which drives stalk cell formation in the developmental
cycle of Dictyostelium discoideum. Previous experiments demonstrated
that the biosynthetic pathway proceeds via dichlorination of the precursor 
molecule THPH, but the enzyme responsible for this transformation has 
eluded characterization. Our recent studies on prokaryotic flavin-dependent 
halogenases and insights from the sequenced Dd genome led us to a 
candidate gene for this transformation. In this work, we present in vivo and 
in vitro evidence that chlA from Dd encodes a flavin-dependent halogenase 
capable of catalyzing both chlorinations in the biosynthesis of DIF-1. The
results provide in vitro characterization of a eukaryotic oxygendependent
halogenase and demonstrate a broad reach in biology for this molecular 
tailoring strategy, notably its involvement in the differentiation program of 
a social amoeba.


Submitted by Christopher S. Neumann [christopher_neumann@hms.harvard.edu]
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[End dictyNews, volume 34, number 8]