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PDBsum entry 1qqj
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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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Crystal structure and mechanism of a carbon-Carbon bond hydrolase.
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Authors
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D.E.Timm,
H.A.Mueller,
P.Bhanumoorthy,
J.M.Harp,
G.J.Bunick.
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Ref.
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Structure, 1999,
7,
1023-1033.
[DOI no: ]
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PubMed id
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Abstract
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BACKGROUND: Fumarylacetoacetate hydrolase (FAH) catalyzes the final step of
tyrosine and phenylalanine catabolism, the hydrolytic cleavage of a
carbon-carbon bond in fumarylacetoacetate, to yield fumarate and acetoacetate.
FAH has no known sequence homologs and functions by an unknown mechanism.
Carbon-carbon hydrolysis reactions are essential for the human metabolism of
aromatic amino acids. FAH deficiency causes the fatal metabolic disease
hereditary tyrosinemia type I. Carbon-carbon bond hydrolysis is also important
in the microbial metabolism of aromatic compounds as part of the global carbon
cycle. RESULTS: The FAH crystal structure has been determined by rapid,
automated analysis of multiwavelength anomalous diffraction data. The FAH
polypeptide folds into a 120-residue N-terminal domain and a 300-residue
C-terminal domain. The C-terminal domain defines an unusual beta-strand topology
and a novel 'mixed beta-sandwich roll' structure. The structure of FAH complexed
with its physiological products was also determined. This structure reveals
fumarate binding near the entrance to the active site and acetoacetate binding
to an octahedrally coordinated calcium ion located in close proximity to a
Glu-His dyad. CONCLUSIONS: FAH represents the first structure of a hydrolase
that acts specifically on carbon-carbon bonds. FAH also defines a new class of
metalloenzymes characterized by a unique alpha/beta fold. A mechanism involving
a Glu-His-water catalytic triad is suggested based on structural observations,
sequence conservation and mutational analysis. The histidine imidazole group is
proposed to function as a general base. The Ca(2+) is proposed to function in
binding substrate, activating the nucleophile and stabilizing a carbanion
leaving group. An oxyanion hole formed from sidechains is proposed to stabilize
a tetrahedral alkoxide transition state. The proton transferred to the carbanion
leaving group is proposed to originate from a lysine sidechain. The results also
reveal the molecular basis for mutations causing the hereditary tyrosinemia type
1.
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Figure 2.
Figure 2. FAH structure, topology and HT1-associated
mutations. (a) A stereo ribbon diagram illustrating the FAH
subunit structure and position of point mutations causing
hereditary tyrosinemia type I is shown. The N-terminal domain is
located at the bottom of the figure. The mixed b-sandwich roll
structure is centrally located in the figure. Helices are
colored red; b strands are colored in shades of blue
corresponding to the b sheet they form; the positions of point
mutations are represented by green spheres; a calcium ion is
colored yellow; acetate carbon and oxygen atoms are respectively
colored orange and red (top of figure). (b) A topology diagram
of the novel FAH b-strand arrangement is shown. b Strands are
numbered in red according to their sequential occurrence in the
polypeptide chain; residue numbering is in black. Sheets A, B
and C are respectively colored in dark, light and medium shades
of blue, as in (a). a Helices are represented by red rectangles.
Figure 2, Figure 3 and Figure 4 and Figure 6b were generated
using MOLSCRIPT [40].
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The above figure is
reprinted
by permission from Cell Press:
Structure
(1999,
7,
1023-1033)
copyright 1999.
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