Advance biocatalyst for the green conversion of 5-hydroxymethylfurfural to a biopolymer precursor...

2,5-Furandicarboxylic acid (FDCA) is a bio-derived compound which serves as a building block of polyethylene furandicarboxylate (PEF) for the synthesis of bio-plastics. 5-Hydroxymethylfurfural oxidase (HMFO) is a promising biocatalyst for the oxidation of 5-hydroxymethylfurfural (HMF) to FDCA through three oxidation steps. The substrate could be fructose and other C6 sugars present in lignocellulosic biomass, providing an eco-friendly and sustainable route for the production of FDCA, an essential monomer for biopolymer development.

The newly identified HMFO enzyme from Pseudomonas poae (PSPO) was heterologously expressed in E. coli, and the recombinant protein was purified and characterized. The catalytic function of PSPO was authenticated for the oxidation of HMF to FDCA. PSPO oxidized HMF, resulting in a 99% yield of FDCA within 24 h. The secondary structure composition of PSPO was analyzed. The optimal enzymatic activity of the recombinant protein was observed at pH 8.0 and temperature of 30℃. PSPO enzyme stability against H₂O₂ was evaluated, and the enzyme was observed to retain ˃90% of residual activity at lower concentrations of H₂O₂ (2 to 6 mM). The kinetic parameters of PSPO for the substrates HMF, FFCA, DFF, and vanillyl alcohol were also determined. The K_m values for HMF, FFCA, DFF, and vanillyl alcohol were 2.252 mM, 5.551 mM, 2.503 mM, and 1.589 mM, respectively.

The identified and characterized PSPO was found to have a potential for the accelerated enzymatic oxidation of HMF to FDCA. Through molecular dynamic (MD) simulations of the catalytic pathway and enzyme mechanisms, alongside assessing the impact of substrate concentration, PSPO turns out to be a potential candidate for enhancing reaction efficiency and maximizing yield.