Process Biochemistry, Vol.56, 124-131, 2017
Ala258Phe substitution in Bacillus sp YX-1 glucose dehydrogenase improves its substrate preference for xylose
Bacillus sp. YX-1 glucose dehydrogenase (BsGDH) with good solvent resistance catalyzes the oxidation of beta-D-glucose to D-glucono-1,5-lactone. Xylose is a recyclable resource from hemicellulase hydrolysis. In this work, to improve the preference of BsGDH for xylose, we designed seven mutants inside or adjacent to the substrate binding pocket using site-directed mutagenesis. Among all mutants, Ala258Phe mutant displayed the highest activity of 7.59 U mg(-1) and nearly 8-folds higher k(cat)/K-m value towards xylose than wild-type BsGDH. The kinetic constants indicated that the A258F mutation effectively altered the transition state. By analysis of modeled protein structure, Ala258Phe created a space to facilitate the reactivity towards xylose. A258F mutant retained good solvent resistance in glycol, ethyl caprylate, octane, decane, cyclohexane, nonane, etc. as with BsGDH. This work provides a protein engineering approach to modify the substrate stereo-preference of alcohol dehydrogenase and a promising enzyme for cofactor regeneration in chiral catalysis. (C) 2017 Elsevier Ltd. All rights reserved.
Keywords:Glucose dehydrogenase;Substrate specificity;Xylose oxidation;Solvent resistance;Site-mutagenesis