2-pyrone-4,6-dicarboxylate lactonase (EC 3.1.1.57, LigI) is an enzyme that catalyzes the reversible hydrolytic reaction
The enzyme characterised from Pseudomonas species hydrolyses 2-oxo-2H-pyran-4,6-dicarboxylic acid to 4-oxalmesaconic acid. The reaction is part of the degradation pathwy for gallic acid. It plays an important role in the metabolism of lignin-derived aromatic compounds in both the syringate degradation pathway and the protocatechuate 4,5-cleavage pathway.
The enzyme belongs to the amidohydrolase superfamily and is a member of Cluster of Orthologous Groups (COG) 3618. LigI from Sphingomonas is of particular interest as it has been shown to be the first amidohydrolase not to require a divalent metal cation for catalytic activity. The systematic name of this enzyme is 2-oxo-2H-pyran-4,6-dicarboxylate lactonohydrolase.
Mechanism The mechanism of catalysis of LigI has been determined by crystallography and NMR analysis. The hydrolytic water molecule is activated by the transfer of a proton to Asp-248 whereas the carbonyl group of the 2-pyrone-4,6-dicarboxylate (PDC) lactone substrate is activated by hydrogen bonding interactions with His-180, His-31, and His-33.
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