title: Structural basis for an atypical active site of an L-aspartate/glutamate-specific racemase from Escherichia coli.
abstract: We determined the crystal structure of EcL-DER to elucidate protein function and substrate specificity. Unlike other asp/glu racemases, EcL-DER has an unbalanced pair of catalytic residues, Thr83/Cys197, at the active site that is crucial for L- to D-unidirectional racemase activity. EcL-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 EcL-DER(C197S) mutant in complex with L-glutamate, we determined the binding mode of the L-glutamate substrate in EcL-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.
authors.affiliation: School of Life Sciences, KNU Creative BioResearch Group, Kyungpook National University, Daehak-ro 80, Buk-ku, Daegu 702-701, Republic of Korea.
authors.forename: Jae-Woo
authors.initials: JW
authors.lastname: Ahn
authors.affiliation: Department of Biology Education, Kyungpook National University, Daehak-ro 80, Buk-ku, Daegu 702-701, Republic of Korea. Electronic address: jhcbio@knu.ac.kr.
authors.forename: Jeong Ho
authors.initials: JH
authors.lastname: Chang
authors.affiliation: School of Life Sciences, KNU Creative BioResearch Group, Kyungpook National University, Daehak-ro 80, Buk-ku, Daegu 702-701, Republic of Korea. Electronic address: kkim@knu.ac.kr.
authors.forename: Kyung-Jin
authors.initials: KJ
authors.lastname: Kim
mesh_terms: D000591:Amino Acid Isomerases / Q000737:chemistry* / Q000378:metabolism*; D000595:Amino Acid Sequence; D001224:Aspartic Acid / Q000378:metabolism*; D020134:Catalytic Domain; D004926:Escherichia coli / Q000201:enzymology*; D008958:Models, Molecular; D008969:Molecular Sequence Data; D013379:Substrate Specificity
chemical_list: D001224:Aspartic Acid; D000591:Amino Acid Isomerases; C062292:glutamate racemase
keywords: Amino acid enantiomer; Asp/glu racemase; Structure; l-Form specific racemase