Structures of glycolate oxidase from Nicotiana benthamiana reveal a conserved pH sensor affecting the binding of FMN

Dual catalytic potential of isoeugenol synthase in Asarum sieboldii Miq. (AsIGS): Unveiling isoeugenol preference in vitro and eugenol production in vivo, with insights into hydrogen bonding influence

Asarum sieboldii Miq. is an important medicinal plant valued for its diverse health benefits in the pharmaceutical industry. In the present study, we isolated and characterized isoeugenol synthase from A. sieboldii (AsIGS), an essential enzyme involved in the biosynthesis of volatile phenylpropenes. We hoped to elucidate the secondary metabolic network of eugenol in A. sieboldii plants, which constructed the prerequisite for quality improvement of the well-known TCM Asari Radix et Rhizoma. Bioinformatics analysis revealed high similarity between the DNA sequences of AsIGS and isoeugenol synthase genes from other plants, and that the association of the candidate protein AsIGS with the PIP reductase family. Moreover, the AsIGS protein displayed a molecular weight of about 34.96 kDa, with a theoretical isoelectric point of 6.01 and an average hydrophobicity of -0.092, indicating the protein's partial acidity, stability, and hydrophilic nature. Phylogenetic analysis showed that AsIGS had a close relationship with isoeugenol synthases and fewer eugenol synthases found in other species. Alphafold2 predicted the structure of the AsIGS protein, and CB-Dock2 predicted the binding sites of the ASIGS-NADPH-coniferyl acetate ternary complex. In vitro enzymatic assay results demonstrated that the optimal temperature of the AsIGS-involved catalysis for coniferyl acetate was 30 °C, and several kinetics parameters were Km (12.21 mM), Vmax (27.9 U/mg), kcat (76.26 s-1), and kcat/Km (6.49 s-1·mM-1). Furthermore, it was also determined that the AsIGS protein had varying performance at different pH levels. While the candidate protein converted coniferyl acetate into both isoeugenol and eugenol at pH 5.5, it just catalyzed the production of isoeugenol at pH 6.5. However, isoeugenol has never been detected in A. sieboldii. Altering AsIGS expression in transgenic plants impacted only eugenol contents. Compared with wild type, overexpression of AsIGS increased eugenol content by 23.3 %, while RNAi-induced down-regulation of AsIGS decreased it by 25.3 %. Taken together, these results confirmed that the AsIGS gene was involved in the biosynthesis of eugenol in A. sieboldii with a dual catalytic potential.

Enhancing the Catalytic Activity of Glycolate Oxidase from Chlamydomonas reinhardtii through Semi-Rational Design

Glycolate oxidase is a peroxisomal flavoprotein catalyzing the oxidation of glycolate to glyoxylate and plays crucial metabolic roles in green algae, plants, and animals. It could serve as a biocatalyst for enzymatic production of glyoxylate, a fine chemical with a wide variety of applications in perfumery, flavor, and the pharmaceutical and agrochemical industries. However, the low catalytic activity of native glycolate oxidase and low levels of active enzyme in heterologous expression limit its practical use in industrial biocatalysis. Herein, the glycolate oxidase from Chlamydomonas reinhardtii (CreGO) was selected through phylogenetic tree analysis, and its low level of soluble expression in E. coli BL21(DE3) was improved through the use of the glutathione thioltransferase (GST), the choice of the vector pET22b and the optimization of induction conditions. The semi-rational design of the fusion enzyme GST-Gly-Ser-Gly-CreGO led to the superior variant GST-Gly-Ser-Gly-CreGO-Y27S/V111G/V212R with the k_cat/K_m value of 29.2 s^-1·mM^-1, which was six times higher than that of the wild type. In contrast to GST-Gly-Ser-Gly-CreGO, 5 mg/mL of crude enzyme GST-Gly-Ser-Gly-CreGO-Y27S/V111G/V212R together with 25 μg/mL of catalase catalyzed the oxidation of 300 mM of methyl glycolate for 8 h, increasing the yield from 50.4 to 93.5%.

Tuning an efficient Escherichia coli whole-cell catalyst expressing l-pantolactone dehydrogenase for the biosynthesis of d-(-)-pantolactone

d-(-)-Pantolactone (DPL) is a key intermediate for the production of d-(+)-pantothenate (vitamin B5). Deracemization of d,l-pantolactone (D,L-PL) through oxidizing l-(+)-pantolactone (LPL) to ketopantoyl lactone (KPL) and subsequently reducing KPL to DPL is a promising route for synthesizing DPL. Herein, a newly mined l-pantolactone dehydrogenase from Rhodococcus hoagie (RhoLPLDH) was used for the oxidative dehydrogenation of LPL. To alleviate inclusion bodies formed by membrane-bound RhoLPLDH intracellular expression in E. coli, strategies involving chaperone assistance and decreasing induction temperature were used to achieve RhoLPLDH soluble expression. To enhance its activity, directed evolution and hydrophilicity-based engineering yielded increased catalytic activity and thermostability. 1M LPL was efficiently converted to KPL by engineering strain CM5 co-expressing RhoLPLDH^{L254I/V241I/I156L/F224Q/N164K} and chaperone. A "two stages in one-pot" method was employed in deracemization of 1M D,L-PL with 91.2% yield. These results demonstrated that CM5 catalyst exhibits great potential in enzyme cascade deracemization for the production of DPL.

Functional Characterization of Sugar Beet M14 Antioxidant Enzymes in Plant Salt Stress Tolerance

Salt stress can cause cellular dehydration, which induces oxidative stress by increasing the production of reactive oxygen species (ROS) in plants. They may play signaling roles and cause structural damages to the cells. To overcome the negative impacts, the plant ROS scavenging system plays a vital role in maintaining the cellular redox homeostasis. The special sugar beet apomictic monosomic additional M14 line (BvM14) showed strong salt stress tolerance. Comparative proteomics revealed that six antioxidant enzymes (glycolate oxidase (GOX), peroxiredoxin (PrxR), thioredoxin (Trx), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), and dehydroascorbate reductase3 (DHAR3)) in BvM14 were responsive to salt stress. In this work, the full-length cDNAs of genes encoding these enzymes in the redox system were cloned from the BvM14. Ectopic expression of the six genes reduced the oxidative damage of transgenic plants by regulating the contents of hydrogen peroxide (H₂O₂), malondialdehyde (MDA), ascorbic acid (AsA), and glutathione (GSH), and thus enhanced the tolerance of transgenic plants to salt stress. This work has charecterized the roles that the antioxidant enzymes play in the BvM14 response to salt stress and provided useful genetic resources for engineering and marker-based breeding of crops that are sensitive to salt stress.

Enzymatic Properties of Recombinant Phospho-Mimetic Photorespiratory Glycolate Oxidases from Arabidopsis thaliana and Zea mays

In photosynthetic organisms, the photorespiratory cycle is an essential pathway leading to the recycling of 2-phosphoglycolate, produced by the oxygenase activity of ribulose-1,5-bisphosphate carboxylase/oxygenase, to 3-phosphoglycerate. Although photorespiration is a widely studied process, its regulation remains poorly understood. In this context, phosphoproteomics studies have detected six phosphorylation sites associated with photorespiratory glycolate oxidases from Arabidopsis thaliana (AtGOX1 and AtGOX2). Phosphorylation sites at T4, T158, S212 and T265 were selected and studied using Arabidopsis and maize recombinant glycolate oxidase (GOX) proteins mutated to produce either phospho-dead or phospho-mimetic enzymes in order to compare their kinetic parameters. Phospho-mimetic mutations (T4D, T158D and T265D) led to a severe inhibition of GOX activity without altering the K_M glycolate. In two cases (T4D and T158D), this was associated with the loss of the cofactor, flavin mononucleotide. Phospho-dead versions exhibited different modifications according to the phospho-site and/or the GOX mutated. Indeed, all T4V and T265A enzymes had kinetic parameters similar to wild-type GOX and all T158V proteins showed low activities while S212A and S212D mutations had no effect on AtGOX1 activity and AtGOX2/ZmGO1 activities were 50% reduced. Taken together, our results suggest that GOX phosphorylation has the potential to modulate GOX activity.