Engineering fructosyl peptide oxidase to improve activity toward the fructosyl hexapeptide standard for HbA1c measurement

The recently discovered fructosyl peptide oxidase from Phaeosphaeria nodorum (PnFPOX) was demonstrated to react with the glycated hexapeptide measurement standard of Hemoglobin A1c, fVHLTPE. The highly reactive Coniochaeta FPOX (FPOX-C) showed no detectable activity with the hexapeptide. Two loop regions were identified as having important effects on the enzymatic properties of FPOX. The first loop has a strong influence on the ability to bind larger glycated peptides, while the second loop has a significant effect on catalytic activity. Loop-substitution mutants showed that the highest activity against fVHLTPE resulted from the combination of the first loop from PnFPOX and the second loop from FPOX-C. The most promising engineered FPOX created, which showed 17-fold greater dehydrogenase activity against fVHLTPE than wild-type PnFPOX, was the FPOX-C mutant with a PnFPOX-derived loop 1 region and an Asn56Ala substitution.