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PDBsum entry 1m1t
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Contents |
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* Residue conservation analysis
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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 catalytic cycle of biosynthetic thiolase: a conformational journey of an acetyl group through four binding modes and two oxyanion holes.
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Authors
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P.Kursula,
J.Ojala,
A.M.Lambeir,
R.K.Wierenga.
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Ref.
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Biochemistry, 2002,
41,
15543-15556.
[DOI no: ]
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PubMed id
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Abstract
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Biosynthetic thiolase catalyzes the formation of acetoacetyl-CoA from two
molecules of acetyl-CoA. This is a key step in the synthesis of many biological
compounds, including steroid hormones and ketone bodies. The thiolase reaction
involves two chemically distinct steps; during acyl transfer, an acetyl group is
transferred from acetyl-CoA to Cys89, and in the Claisen condensation step, this
acetyl group is further transferred to a second molecule of acetyl-CoA,
generating acetoacetyl-CoA. Here, new crystallographic data for Zoogloea
ramigera biosynthetic thiolase are presented, covering all intermediates of the
thiolase catalytic cycle. The high-resolution structures indicate that the
acetyl group goes through four conformations while being transferred from
acetyl-CoA via the acetylated enzyme to acetoacetyl-CoA. This transfer is
catalyzed in a rigid cavity lined by mostly hydrophobic side chains, in addition
to the catalytic residues Cys89, His348, and Cys378. The structures highlight
the importance of an oxyanion hole formed by a water molecule and His348 in
stabilizing the negative charge on the thioester oxygen atom of acetyl-CoA at
two different steps of the reaction cycle. Another oxyanion hole, composed of
the main chain nitrogen atoms of Cys89 and Gly380, complements a negative charge
of the thioester oxygen anion of the acetylated intermediate, stabilizing the
tetrahedral transition state of the Claisen condensation step. The reactivity of
the active site may be modulated by hydrogen bonding networks extending from the
active site toward the back of the molecule.
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