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PDBsum entry 2i3c
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References listed in PDB file
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Key reference
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Title
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Structure of aspartoacylase, The brain enzyme impaired in canavan disease.
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Authors
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E.Bitto,
C.A.Bingman,
G.E.Wesenberg,
J.G.Mccoy,
G.N.Phillips.
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Ref.
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Proc Natl Acad Sci U S A, 2007,
104,
456-461.
[DOI no: ]
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PubMed id
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Abstract
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Aspartoacylase catalyzes hydrolysis of N-acetyl-l-aspartate to aspartate and
acetate in the vertebrate brain. Deficiency in this activity leads to spongiform
degeneration of the white matter of the brain and is the established cause of
Canavan disease, a fatal progressive leukodystrophy affecting young children. We
present crystal structures of recombinant human and rat aspartoacylase refined
to 2.8- and 1.8-A resolution, respectively. The structures revealed that the
N-terminal domain of aspartoacylase adopts a protein fold similar to that of
zinc-dependent hydrolases related to carboxypeptidases A. The catalytic site of
aspartoacylase shows close structural similarity to those of carboxypeptidases
despite only 10-13% sequence identity between these proteins. About 100
C-terminal residues of aspartoacylase form a globular domain with a two-stranded
beta-sheet linker that wraps around the N-terminal domain. The long channel
leading to the active site is formed by the interface of the N- and C-terminal
domains. The C-terminal domain is positioned in a way that prevents productive
binding of polypeptides in the active site. The structures revealed that
residues 158-164 may undergo a conformational change that results in opening and
partial closing of the channel entrance. We hypothesize that the catalytic
mechanism of aspartoacylase is closely analogous to that of carboxypeptidases.
We identify residues involved in zinc coordination, and propose which residues
may be involved in substrate binding and catalysis. The structures also provide
a structural framework necessary for understanding the deleterious effects of
many missense mutations of human aspartoacylase.
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Figure 1.
Fig. 1. Ribbon diagrams of the rASPA monomer and dimer. (A)
N-domain of rASPA is color-coded in cyan and red. C-domain is
color-coded in yellow and green. Residues His-21, Gly-22,
Glu-24, Asn-54, Arg-63, Asn-70, Arg-71, Phe-73, Asp-114,
His-116, and Glu-178 (blue sticks) are highly conserved in the
AstE-AspA family and delineate the active site. Zn^2+ is shown
as a pink sphere. (B) The rASPA dimer observed in the asymmetric
unit of the rASPA crystals is shown in ribbon representation.
Both the N-domain (red) and C-domain (green) of the rASPA
monomers are involved in formation of the dimer interface.
Residues His-21, Glu-24, and His-116 (blue sticks) coordinate
Zn^2+ (pink sphere).
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Figure 4.
Fig. 4. Proposed mechanism of action of ASPA.
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