Characterization of d-xylose reductase, XyrB, from Aspergillus niger

•XyrB is involved in conversion of d-xylose and l-arabinose in A. niger.•The xyrB expression is induced both by d-xylose and l-arabinose.•XyrB expression is controlled by xlnR and araR regulators. d-xylose reductase is a member of the aldo-keto reductase family, and is involved in d-xylose and l-arabinose conversion through the Pentose Catabolic Pathway (PCP) in fungi. In this study, we biochemically characterized a newly identified second d-xylose reductase (XyrB) from Aspergillus niger. This NADPH-dependent reductase is able to efficiently convert d-xylose and l-arabinose, and it has the highest affinity for these sugars of all currently known fungal pentose reductases. A combination of biochemical data, transcriptomics and phylogenetic analysis further illustrated the role of XyrB in the PCP. Enzymes: D-xylose reductase (EC 1.1.1.307), L-arabinose reductase (EC 1.1.1.21).