Biochemical characterization of a novel arabinose isomerase for rare sugar production and optimization through enzyme immobilization

The global rise in diabetes and obesity has increased the demand for healthier sugar alternatives. D-tagatose, a low-calorie natural sweetener, is a promising substitute. It can be produced by chemical or enzymatic methods, with enzymes offering advantages such as fewer by-products and milder reaction conditions. This study aimed to characterize a novel L-arabinose isomerase (AraR) to improve biocatalyst efficiency and explore enzyme immobilization for process optimization. The three-dimensional structure of AraR was predicted using AlphaFold to gain insights into its catalytic mechanism. AraR was expressed in Escherichia coli BL21 (DE3) using the pET28a vector and purified via affinity and gel filtration chromatography. Its activity was tested based on the conversion of D-galactose to D-tagatose using a colorimetric assay. AraR showed optimal activity at 40-50 °C and pH 6.0-6.5. Kinetic parameters were V_max 20.75 μM/min and K_m 5.552 mM for L-arabinose, and V_max 20.08 μM/min and K_m 13.50 mM for D-tagatose. Immobilization increased the optimal temperature to 50-60 °C, enhanced thermal stability at 40-50 °C, and extended enzyme half-life, maintaining full activity for 28 days. Structural modeling revealed AraR has three domains and shares architectural similarity with known L-arabinose isomerase.