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Structural basis for an atypical active site of an l ‐aspartate/glutamate‐specific racemase from Escherichia coli
Author(s) -
Ahn Jae-Woo,
Chang Jeong Ho,
Kim Kyung-Jin
Publication year - 2015
Publication title -
febs letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.593
H-Index - 257
eISSN - 1873-3468
pISSN - 0014-5793
DOI - 10.1016/j.febslet.2015.11.003
Subject(s) - glutamate receptor , active site , substrate (aquarium) , chemistry , stereochemistry , mutant , biochemistry , enzyme , biology , receptor , ecology , gene
We determined the crystal structure of Ec L‐DER to elucidate protein function and substrate specificity. Unlike other asp/glu racemases, Ec L‐DER has an unbalanced pair of catalytic residues, Thr83/Cys197, at the active site that is crucial for l ‐ to d ‐unidirectional racemase activity. Ec L‐DER exhibited racemase activity for both l ‐glutamate and l ‐aspartate, but had threefold higher activity for l ‐glutamate. Based on the structure of the Ec L‐DER C197S mutant in complex with l ‐glutamate, we determined the binding mode of the l ‐glutamate substrate in Ec L‐DER and provide a structural basis for how the protein utilizes l ‐glutamate as a main substrate. The unidirectionality, despite an equilibrium constant of unity, can be understood in terms of the Haldane relationship.