Efficient synthesis of 5-hydroxymethyl-2-furancarboxylic acid from bio-based high-concentration 5-hydroxymethylfurfural via highly tolerant aldehyde dehydrogenase

The important bio-based platform chemical 5-Hydroxymethylfurfural (HMF) can be oxidized for use in several products that serve as versatile building blocks of polymers. Previously, we had demonstrated that Pseudomonas aeruginosa PC-1 can selectively produce 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) from 800 mM HMF, with a yield greater than 90%. In this study, an aldehyde dehydrogenase (PaALDH64) was identified from P. aeruginosa PC-1 for selective HMF oxidation to HMFCA. The HMF tolerance level of E. coli/pET-PaALDH64 was over 300 mM, which was greater than the tolerance levels of all other reported enzymes. The proposed biocatalyst could be used to catalyze the biotransformation of other aldehydic furans, with carboxylic acid yields over 92%. Molecular docking revealed that the catalytic active site cleft in PaALDH64 formed more hydrogen bonds with HMF compared to other enzymes, which stabilized the enzyme–substrate interaction and enhanced the catalytic efficiency. In a fed-batch process, 547.8 mM HMFCA was produced from 600 mM HMF by E. coli/pET-PaALDH64 within 19 h only, which showed an excellent HMF conversion rate. Overall, PaALDH64 constitutes a promising enzyme for the industrial production of HMFCA.