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PDBsum entry 3f6h
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References listed in PDB file
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Key reference
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Title
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Molecular basis of the inhibitor selectivity and insights into the feedback inhibition mechanism of citramalate synthase from leptospira interrogans.
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Authors
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P.Zhang,
J.Ma,
Z.Zhang,
M.Zha,
H.Xu,
G.Zhao,
J.Ding.
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Ref.
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Biochem J, 2009,
421,
133-143.
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PubMed id
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Abstract
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LiCMS (Leptospira interrogans citramalate synthase) catalyses the first reaction
of the isoleucine biosynthesis pathway in L. interrogans, the pathogen of
leptospirosis. The catalytic reaction is regulated through feedback inhibition
by its end product isoleucine. To understand the molecular basis of the high
selectivity of the inhibitor and the mechanism of feedback inhibition, we
determined the crystal structure of LiCMSC (C-terminal regulatory domain of
LiCMS) in complex with isoleucine, and performed a biochemical study of the
inhibition of LiCMS using mutagenesis and kinetic methods. LiCMSC forms a dimer
of dimers in both the crystal structure and solution and the dimeric LiCMSC is
the basic functional unit. LiCMSC consists of six beta-strands forming two
anti-parallel beta-sheets and two alpha-helices and assumes a betaalphabeta
three-layer sandwich structure. The inhibitor isoleucine is bound in a pocket at
the dimer interface and has both hydrophobic and hydrogen-bonding interactions
with several conserved residues of both subunits. The high selectivity of LiCMS
for isoleucine over leucine is primarily dictated by the residues, Tyr430,
Leu451, Tyr454, Ile458 and Val468, that form a hydrophobic pocket to accommodate
the side chain of the inhibitor. The binding of isoleucine has inhibitory
effects on the binding of both the substrate, pyruvate, and coenzyme,
acetyl-CoA, in a typical pattern of K-type inhibition. The structural and
biochemical data from the present study together suggest that the binding of
isoleucine affects the binding of the substrate and coenzyme at the active site,
possibly via conformational change of the dimer interface of the regulatory
domain, leading to inhibition of the catalytic reaction.
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