Construction and Characterization of Composite Biocatalysts

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We analyzed the mechanism of biosynthesis of iron-sulfur clusters, which are useful as components of composite biocatalysts. We also developed novel processes for the production of chiral compounds by the use of novel composite biocatalysts. In addition, reaction mechanisms of several composite biocatalysts such as amino acid racemases which require pyridoxal phosphate as a coenzyme were clarified.1. Sulfur atoms of iron-sulfur clusters are supplied from L-cysteine by the sulfur-elimination reaction catalyzed by cysteine desulfurases. We studied the detailed mechanisms of iron-sulfur cluster assembly involving the following cysteine desulfurases : IscS and SufS from Escherichia coli and SsCsd3 from Synechocystis sp. PCC6803. Interactions between these cysteine desulfurases and proteins functioning as scaffold proteins for the assembly of iron-sulfur clusters were analyzed.2. We isolated and characterized a novel NADPH enzyme, N-methyl-L-amino acid dehydrogenase. The gene coding for this enzyme was cloned from Pseudomonas putida ATCC12633, and its overexpression system was constructed. Using this enzyme, we developed an enzymatic process in which chiral N-methyl-L-amino acids are produced from α-keto acids and methylamine.3. We isolated and characterized a novel NADPH enzyme that ctalyzes the asymmetric reduction of a carbon-carbon double bond in halogenated unsaturated compounds. We developed an enzymatic process in which (S)-2-CPA, which is used as a building block for the synthesis of aryloxyphenoxypropionic acid herbicide, is produced by asymmetric reduction of a carbon-carbon double bond in 2-chloroacrylate.