Biochemical and structural characterization of a novel -isoleucine-4-dioxygenase (RaIDO) from Rahnella aquatilis.

The -isoleucine-4-dioxygenase converts -isoleucine (Ile) into(2S,3R,4S)-4-(OH)-isoleucine (4-HIL), a naturally occurring hydroxyl amino acid, which is a promising compound for drug and functional food development. Here, a novel -isoleucine-4-dioxygenase (RaIDO) from Rahnella aquatilis was cloned, expressed and characterized, as one of only a few reported -isoleucine-4-dioxygenases. RaIDO showed high catalytic efficiency with Ile as the substrate, as well as good stability. HPLC-MS and NMR confirmed that RaIDO converts Ile into (2S,3R,4S)-4-(OH)-isoleucine. Further, structural analysis of RaIDO revealed key active site residues, including H159, D161 and H212. The RaIDO enzyme showed an optimal reaction temperature range of 30°C-45 °C, with the highest catalytic activity observed at 40 °C. Additionally, the enzyme exhibited an optimal pH of 8.0. Thus, the novel -isoleucine-4-dioxygenase (RaIDO) has high catalytic efficiency and good stability, making it a strong candidate for industrial applications.