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PDBsum entry 1kko
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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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Insights into enzyme evolution revealed by the structure of methylaspartate ammonia lyase.
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Authors
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C.W.Levy,
P.A.Buckley,
S.Sedelnikova,
Y.Kato,
Y.Asano,
D.W.Rice,
P.J.Baker.
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Ref.
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Structure, 2002,
10,
105-113.
[DOI no: ]
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PubMed id
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Abstract
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Methylaspartate ammonia lyase (MAL) catalyzes the magnesium-dependent reversible
alpha,beta-elimination of ammonia from L-threo-(2S,3S)-3-methylaspartic acid to
mesaconic acid. The 1.3 A MAD crystal structure of the dimeric Citrobacter
amalonaticus MAL shows that each subunit comprises two domains, one of which
adopts the classical TIM barrel fold, with the active site at the C-terminal end
of the barrel. Despite very low sequence similarity, the structure of MAL is
closely related to those of representative members of the enolase superfamily,
indicating that the mechanism of MAL involves the initial abstraction of a
proton alpha to the 3-carboxyl of (2S,3S)-3-methylasparic acid to yield an
enolic intermediate. This analysis resolves the conflict that had linked MAL to
the histidine and phenylalanine ammonia lyase family of enzymes.
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Figure 5.
Figure 5. A Schematic of the Proposed Reaction Mechanism of
MALThe 3-proton of (2S,3S)-3-methyl aspartic acid is abstracted
by Lys-331 acting as a base to give the enolic intermediate
shown in the middle panel. The negative charge on the
aci-carboxylate is stabilized by the metal ion and possibly by
His-194 acting as an electrophile. The enolic intermediate
collapses with the elimination of ammonia to yield mesaconic
acid (right hand panel).
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The above figure is
reprinted
by permission from Cell Press:
Structure
(2002,
10,
105-113)
copyright 2002.
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