Title:
Contributions of active site residues to substrate binding and catalysis of 5-nitroanthranilic acid aminohydrolase
Contributions of active site residues to substrate binding and catalysis of 5-nitroanthranilic acid aminohydrolase
Author(s)
Tao, Xingjian
Advisor(s)
Lieberman, Raquel L.
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Abstract
Synthetic and naturally occurring nitroaromatic compounds are recalcitrant to degradation and they are toxic/mutagenic. The symbiont Bradyrhizobium sp. JS329 is the first microbe found to degrade a biological nitroaromatic compound, 5-nitroanthralinic acid (5NAA), which is secreted by the bacterium responsible for potato scabs, Streptomyces scabies. The first enzyme in the degradation pathway is 5NAA-aminohydrolase (5NAA-A), a metalloprotease family member that has evolved to hydrolyze 5NAA to 5-nitrosalicylic acid. 5NAA-A is the first characterized metalloenzyme to utilize nucleophilic aromatic substitution. Here, I used isothermal titration calorimetry, enzyme activity assays, and X-ray crystallography to dissect contributions of individual active site and second-shell residues for assisting substrate transport. My studies demonstrate the interplay between substrate binding and catalysis requirements for this unusual metalloenzyme. Knowledge of the 5NAA-A structure and mechanism informs potential bioremediation and biocatalytic approaches to mitigate the environmental and ecological impact of nitroaromatic and other challenging substrates.
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Date Issued
2019-04-30
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