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PDBsum entry 1yyr
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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 recognition of the substrate diphosphate group governs product diversity in trichodiene synthase mutants.
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Authors
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L.S.Vedula,
M.J.Rynkiewicz,
H.J.Pyun,
R.M.Coates,
D.E.Cane,
D.W.Christianson.
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Ref.
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Biochemistry, 2005,
44,
6153-6163.
[DOI no: ]
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PubMed id
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Abstract
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The X-ray crystal structures of Y305F trichodiene synthase and its complex with
coproduct inorganic pyrophosphate (PP(i)) and of Y305F and D100E trichodiene
synthases in ternary complexes with PP(i) and aza analogues of the bisabolyl
carbocation intermediate are reported. The Y305F substitution in the basic
D(302)RRYR motif does not cause large changes in the overall structure in
comparison with the wild-type enzyme in either the uncomplexed enzyme or its
complex with PP(i). However, the loss of the Y305F-PP(i) hydrogen bond appears
to be compensated by a very slight shift in the position of the side chain of
R304. The putative bisabolyl carbocation mimic, R-azabisabolene, binds in a
conformation and orientation that does not appear to mimic that of the actual
carbocation intermediate, suggesting that the avid inhibition by R- and
S-azabisabolenes arises more from favorable electrostatic interactions with
PP(i) rather than any special resemblance to a reaction intermediate. Greater
enclosed active-site volumes result from the Y305F and D100E mutations that
appear to confer greater variability in ligand-binding conformations and
orientations, which results in the formation of aberrant cyclization products.
Because the binding conformations and orientations of R-azabisabolene to Y305F
and D100E trichodiene synthases do not correspond to binding conformations
required for product formation and because the binding conformations and
orientations of diverse substrate and carbocation analogues to other cyclases
such as 5-epi-aristolochene synthase and bornyl diphosphate synthase generally
do not correspond to catalytically productive complexes, we conclude that the
formation of transient carbocation intermediates in terpene cyclization
reactions is generally under kinetic rather than thermodynamic control.
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