Download MendeleyKinetic and Crystallographic Analysis of Active Site Mutants of Escherichia coligamma-Aminobutyrate Aminotransferase.
Liu, W., Peterson, P.E., Langston, J.A., Jin, X., Zhou, X., Fisher, A.J., Toney, M.D.(2005) Biochemistry 44: 2982-2992
- PubMed: 15723541
- DOI: https://doi.org/10.1021/bi048657a
- Primary Citation of Related Structures:
1SZK, 1SZS, 1SZU - PubMed Abstract:
The E. coli isozyme of gamma-aminobutyrate aminotransferase (GABA-AT) is a tetrameric pyridoxal phosphate-dependent enzyme that catalyzes transamination between primary amines and alpha-keto acids. The roles of the active site residues V241, E211, and I50 in the GABA-AT mechanism have been probed by site-directed mutagenesis. The beta-branched side chain of V241 facilitates formation of external aldimine intermediates with primary amine substrates, while E211 provides charge compensation of R398 selectively in the primary amine half-reaction and I50 forms a hydrophobic lid at the top of the substrate binding site. The structures of the I50Q, V241A, and E211S mutants were solved by X-ray crystallography to resolutions of 2.1, 2.5, and 2.52 A, respectively. The structure of GABA-AT is similar in overall fold and active site structure to that of dialkylglycine decarboxylase, which catalyzes both transamination and decarboxylation half-reactions in its normal catalytic cycle. Therefore, an attempt was made to convert GABA-AT into a decarboxylation-dependent aminotransferase similar to dialkylglycine decarboxylase by systematic mutation of E. coli GABA-AT active site residues. Two of the twelve mutants presented, E211S/I50G/C77K and E211S/I50H/V80D, have approximately 10-fold higher decarboxylation activities than the wild-type enzyme, and the E211S/I50H/V80D has formally changed the reaction specificity to that of a decarboxylase.
Organizational Affiliation:
Department of Chemistry, University of California-Davis, Davis, California 95616, USA.
