Single Amino Acid Mutation of Pyranose 2-Oxidase Results in Increased Specificity for Diabetes Biomarker 1,5-Anhydro-D-Glucitol

Abstract

Pyranose 2-oxidases catalyze the oxidation of various pyranose sugars at the C2 position. However, their potential application for detecting sugars other than glucose in blood is hindered by relatively high activity towards glucose. In this study, in order to find a mutant enzyme with enhanced specificity for 1,5-anhydro-D-glucitol (1,5-AG), which is a biomarker for diabetes mellitus, we conducted site-directed mutagenesis of pyranose 2-oxidase from the basidiomycete Phanerochaete chrysosporium (PcPOX). Considering the three-dimensional structure of the substrate-binding site of PcPOX and the structural difference between glucose and 1,5-AG, we selected alanine 551 of PcPOX as a target residue for mutation. Kinetic studies of the 19 mutants of PcPOX expressed as recombinant proteins in E. coli revealed that the ratio of k_cat/K_m for 1,5-AG to k_cat/K_m for glucose was three times higher for the A551L mutant than for wild-type PcPOX. Although the A551L mutant has lower specific activity towards each substrate than the wild-type enzyme, its increased specificity for 1,5-AG makes it a promising lead for the development of POX-based 1,5-AG detection systems.