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PDBsum entry 3ept
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Oxidoreductase
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PDB id
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3ept
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References listed in PDB file
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Key reference
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Title
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The FAD cofactor of rebc shifts to an in conformation upon flavin reduction.
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Authors
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K.S.Ryan,
S.Chakraborty,
A.R.Howard-Jones,
C.T.Walsh,
D.P.Ballou,
C.L.Drennan.
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Ref.
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Biochemistry, 2008,
47,
13506-13513.
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PubMed id
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Abstract
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RebC is a putative flavin hydroxylase functioning together with RebP to carry
out a key step in the biosynthesis of rebeccamycin. To probe the mechanism of
flavin-based chemistry in RebC, we solved the structure of RebC with reduced
flavin. Upon flavin reduction, the RebC crystal undergoes a change in its unit
cell dimension concurrent with a 5 A movement of the isoalloxazine ring,
positioning the flavin ring adjacent to the substrate-binding pocket.
Additionally, a disordered helix becomes ordered upon flavin reduction, closing
off one side of the substrate-binding pocket. This structure, along with
previously reported structures, increases our understanding of the RebC enzyme
mechanism, indicating that either the reduction of the flavin itself or binding
of substrate is sufficient to drive major conformational changes in RebC to
generate a closed active site. Our finding that flavin reduction seals the
active site such that substrate cannot enter suggests that our reduced flavin
RebC structure is off-pathway and that substrate binding is likely to precede
flavin reduction during catalysis. Along with kinetic data presented here, these
structures suggest that the first cycle of catalysis in RebC may resemble that
of p-hydroxybenzoate hydroxylase, with substrate binding promoting flavin
reduction.
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