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CSA entry for 1kcz
Original Entry
Title:
Lyase
Compound:
Beta-methylaspartase
Mutant:
No
UniProt/Swiss-Prot:
Q05514-MAAL_CLOTT
EC Class:
4.3.1.2
Other CSA Entries:
Overview of all sites for 1kcz
Homologues of 1kcz
Entries for UniProt/Swiss-Prot: Q05514
Entries for EC: 4.3.1.2
Other Databases:
PDB entry: 1kcz
PDBsum entry: 1kcz
UniProt/Swiss-Prot: Q05514
IntEnz entry: 4.3.1.2
Literature Report:
Introduction:
Methylasparate ammonium lyase (MAL) catalyses the reversible elimination of ammonia from L-threo-(2S,3S)-3-methylaspartate to mesaconate. It will also catalyse the stereo- and regioselective addition of ammonia to several derivatives of mesaconic acid to give a limited number of homochiral substituted aspartic acids. The structure of MAL is similar to that of members of the enolase superfamily, which all catalyse removal of a proton alpha to a carboxylic acid as the first step in their mechanism.
Mechanism:
Lys 331 acts as a general base to remove the 3-proton from 3-methyl aspartate to generate an enolic intermediate. An Mg2+ ion and His 194 provide positive charges to stabilise the accumulation of negative charge on the substrate carboxyl group during the formation of this intermediate. Collapse of the enolate leads to elimination of ammonia in an E1cB mechanism.
Sites:

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Found by:
Literature reference 

ResidueChainNumberUniProt numberFunctional part FunctionTargetDescription
HISA 194 194Sidechain
ElectrostaticTransition state
Provides a positive charge to stabilise the negative charge that accumulates in the enolate intermediate following abstraction of the 3-proton.
Evidence from paper Evidence concerns Evidence type
PubMed ID 11796115 Current protein Structural similarity to homologue of known mechanism
PubMed ID 11796115 Current protein Residue is positioned appropriately (ligand position known)

ResidueChainNumberUniProt numberFunctional part FunctionTargetDescription
LYSA 331 331Sidechain
Acid/baseSubstrate
Acts as a general base to remove the 3-proton and generate an enolic intermediate.
Evidence from paper Evidence concerns Evidence type
PubMed ID 11796115 Current protein Residue is positioned appropriately (ligand position known)
PubMed ID 11796115 Current protein Structural similarity to homologue of known mechanism
PubMed ID 11796115 Current protein Conservation of residue

ResidueChainNumberUniProt numberFunctional part FunctionTargetDescription
MGA 901 0
ElectrostaticTransition state
Stabilises the enolate intermediate the develops after abstraction of the 3-proton, in effect lowering the pKa of this proton.
Evidence from paper Evidence concerns Evidence type
PubMed ID 11796115 Current protein Ligand is essential for catalysis
PubMed ID 11796115 Current protein Structural similarity to homologue of known mechanism
PubMed ID 11796115 Current protein Residue is positioned appropriately (ligand position known)
References:
1
The structure of 3-methylaspartase from Clostridium tetanomorphum functions via the common enolase chemical step
M. Asuncion and W. Blankenfeldt and J. N. Barlow and D. Gani and J. H. Naismith
J Biol Chem. 277 (10) 8306-11, (2002)
11748244
2
Insights into enzyme evolution revealed by the structure of methylaspartate ammonium lyase
C. W. Levy and P. A. Buckley and S. Sedelnikova and Y. Kato and Y. Asano and D. W. Rice and P. J. Baker
Structure (Camb) 10 (1) 105-13, (2002)
11796115
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