Pycnoporus cinnabarinus glyoxal oxidases display differential catalytic efficiencies on 5-hydroxymethylfurfural and its oxidized derivatives

Abstract

Background 5-Hydroxymethylfurfural (HMF), a major residual component of a lignocellulosic bio-refinery process, can be transformed into fundamental building blocks for green chemistry via oxidation. While chemical methods are well established, interest is also being directed into the enzymatic oxidation of HMF into the bio-plastic precursor 2,5-furandicarboxylic acid (FDCA). Results We demonstrate that three glyoxal oxidases ( Pci GLOX) isoenzymes from the Basidiomycete fungus Pycnoporus cinnabarinus were able to oxidize HMF, with Pci GLOX2 and Pci GLOX3 being the most efficient. The major reaction product obtained with the three isoenzymes was 5-hydroxymethyl-2-furancarboxylic (HMFCA), a precursor in polyesters and pharmaceuticals production, and very little subsequent conversion of this compound was observed. However, small concentrations of FDCA, a substitute for terephthalic acid in the production of polyesters, were also obtained. The oxidation of HMF was significantly boosted in the presence of catalase for Pci GLOX2, leading to 70% HMFCA yield. The highest conversion percentages were observed on 2,5-furandicarboxaldehyde (DFF), a minor product from the reaction of Pci GLOX on HMF. To bypass HMFCA accumulation and exploit the efficiency of Pci GLOX in oxidizing DFF and 5-formyl-2-furan carboxylic acid (FFCA) towards FDCA production, HMF was oxidized in a cascade reaction with an aryl alcohol oxidase ( Uma AAO). After 2 h of reaction, Uma AAO completely oxidized HMF to DFF and further to FFCA, with FDCA only being detected when Pci GLOX3 was added to the reaction. The maximum yield of 16% FDCA was obtained 24 h after the addition of Pci GLOX3 in the presence of catalase. Conclusions At least two conversion pathways for HMF oxidation can be considered for Pci GLOX; however, the highest selectivity was seen towards the production of the valuable polyester precursor HMFCA. The three isoenzymes showed differences in their catalytic efficiencies and substrate specificities when reacted with HMF derivatives. Electronic supplementary material The online version of this article (10.1186/s40694-019-0067-8) contains supplementary material, which is available to authorized users.

Screening and Evaluation of New Hydroxymethylfurfural Oxidases for Furandicarboxylic Acid Production

“…In contrast, Dijkman et al ( 14 ) still detected DFF after 1 h of reaction between 2 mM HMF or DFF and 1 μM HMFO, while according to their k cat value, all DFF should be consumed in ∼20 min. In any case, the k cat and K m values for oxidation of these furfural derivatives by the Metsp HMFO produced here are of the same order as those previously reported for other oxidases acting on these substrates, such as AAO ( 19 ) and GLOX ( 21 ). Regarding FFCA, the catalytic efficiency, estimated as k obs /[FFCA], was of the same order as that previously reported for Metsp HMFO ( 12 ), although the strong inhibition by FFCA (above 3 mM) has not been described before.…”

“…peroxygenase (15,20), GLOX/AAO (21) or AAO/catalase (16) couples, already reported. Therefore, MetspHMFO is the only enzyme described to date able to perform by itself (i.e.…”

“…More recently, a new copper radical oxidase from Colletotrichum graminicola has been described as an AAO-type enzyme and reported to oxidize HMF into DFF and 5-hydroxymethylfurancarboxylic acid (HMFCA) into FFCA without detected activity on the aldehyde groups of these compounds ( 17 ). Due to the above-named characteristics, efficient production of FDCA by the latter oxidases requires the combination of several enzymes, such as the AAO/chloroperoxidase ( 18 ), AAO/peroxygenase ( 15 , 19 ), GAO/peroxygenase ( 15 , 20 ), GLOX/AAO ( 21 ), or AAO/catalase ( 16 ) couples already reported. Therefore, Metsp HMFO is the only enzyme described to date able to perform by itself (i.e., without the concourse of a second enzyme) the three oxidation steps for FDCA production from HMF.…”

A Putative Lignin Copper Oxidase from Trichoderma reesei

“…As a component of the secreted enzymatic arsenal utilized by fungi, the copper radical oxidases (CRO, previously also known as radical-copper oxidases; [ 30 ]) have generally been regarded as an accessory enzyme in the ligninolysis process, generating H 2 O 2 for the heavy cleavage action of peroxidases [ 31 ]. They have subsequently been found to require themselves the presence of a peroxidase or catalase in a two-fold mechanistic function: (1) to utilize the H 2 O 2 produced during catalysis and thus avoid auto-inactivation, and (2) for full activation of the resting state of the CRO [ 32 , 33 , 34 ]. The genes encoding CROs are widely distributed in the Fungal Kingdom, and the copper-binding catalytic center is well preserved.…”

Two Fusarium copper radical oxidases with high activity on aryl alcohols

“…Fgr AAO and Fox AAO display similar specificity constants on HMF to the eponymous bacterial HMF oxidase (a GMC superfamily oxidoreductase) [ 73 ], and exhibit higher specificity constants than other enzymes with HMF oxidase activity, including some glyoxal oxidases from AA5_1 (Additional file 1 : Table S5) [ 70 , 71 , 74 ]. However, the recently reported Cgr AAO [ 19 ] has tenfold higher activity on HMF than both Fgr AAO and Fox AAO (Additional file 1 : Table S5).…”