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PDBsum entry 1h4f
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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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Fatty acid synthesis.
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Authors
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P.Von wettstein-Knowles,
J.G.Olsen,
K.A.Mcguire,
A.Henriksen.
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Ref.
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FEBS J, 2006,
273,
695-710.
[DOI no: ]
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PubMed id
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Abstract
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beta-Ketoacyl-acyl carrier protein (ACP) synthase enzymes join short carbon
units to construct fatty acyl chains by a three-step Claisen condensation
reaction. The reaction starts with a trans thioesterification of the acyl primer
substrate from ACP to the enzyme. Subsequently, the donor substrate malonyl-ACP
is decarboxylated to form a carbanion intermediate, which in the third step
attacks C1 of the primer substrate giving rise to an elongated acyl chain. A
subgroup of beta-ketoacyl-ACP synthases, including mitochondrial
beta-ketoacyl-ACP synthase, bacterial plus plastid beta-ketoacyl-ACP synthases I
and II, and a domain of human fatty acid synthase, have a Cys-His-His triad and
also a completely conserved Lys in the active site. To examine the role of these
residues in catalysis, H298Q, H298E and six K328 mutants of Escherichia
colibeta-ketoacyl-ACP synthase I were constructed and their ability to carry out
the trans thioesterification, decarboxylation and/or condensation steps of the
reaction was ascertained. The crystal structures of wild-type and eight mutant
enzymes with and/or without bound substrate were determined. The H298E enzyme
shows residual decarboxylase activity in the pH range 6-8, whereas the H298Q
enzyme appears to be completely decarboxylation deficient, showing that H298
serves as a catalytic base in the decarboxylation step. Lys328 has a dual role
in catalysis: its charge influences acyl transfer to the active site Cys, and
the steric restraint imposed on H333 is of critical importance for
decarboxylation activity. This restraint makes H333 an obligate hydrogen bond
donor at N(epsilon), directed only towards the active site and malonyl-ACP
binding area in the fatty acid complex.
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Figure 1.
Fig. 1. Superimposition of the KAS I C163S-C12 (white,
light colors) [3] and KAS I–C8 (gray, dark colors) active
sites. Red spheres are water molecules. Blue atoms represent
nitrogen, red represent oxygen, and green represents sulfur.
Figures 1, 2 and 4 are made in MOLSCRIPT[41].
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Figure 3.
Fig. 3. The active sites of the wild-type KAS I, its H298
mutants and their acyl complexes. (A) Wild-type. (B) WT–C8.
(C) Superimposition of the wild-type (white, light colors) and
H298E (orange, dark colors). (D) H298E. (E) H298E–C12. (F)
H298Q. (G) H298Q–C12. (H) Superimposition of H298Q and
H298Q–C12. In (A, B) and (D–G), water molecules (red
spheres) within hydrogen bonding distance are indicated with
dashed lines. (H) Superimposition of H298Q (orange, dark colors)
and H298Q–C12 (white, light colors) not including water
molecules. Figure prepared using PYMOL[42].
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The above figures are
reprinted
by permission from the Federation of European Biochemical Societies:
FEBS J
(2006,
273,
695-710)
copyright 2006.
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Secondary reference #1
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Title
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Structures of beta-Ketoacyl-Acyl carrier protein synthase i complexed with fatty acids elucidate its catalytic machinery.
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Authors
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J.G.Olsen,
A.Kadziola,
P.Von wettstein-Knowles,
M.Siggaard-Andersen,
S.Larsen.
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Ref.
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Structure, 2001,
9,
233-243.
[DOI no: ]
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PubMed id
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Figure 1.
Figure 1. The Three-Step Mechanism Characterizing the
Decarboxylating Claisen Condensing EnzymesThe first step is a
trans-thioesterification of the primer substrate. Subsequently,
malonyl-ACP gets decarboxylated to give the carbanion, which
then attacks C1 of the primer substrate, followed by release of
the product, 3-oxoacyl-ACP
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The above figure is
reproduced from the cited reference
with permission from Cell Press
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