P-hydroxybenzoate Hydroxylase Research Articles

Structure, dimeric conformation, and coenzyme versatility of p-hydroxybenzoate hydroxylase from Arthrobacter sp. PAMC25564

p-Hydroxybenzoate hydroxylase (PHBH) catalyzes the ortho-hydroxylation of 4-hydroxybenzoate (4-HB) to protocatechuate (PCA). PHBHs are commonly known as homodimers, and the prediction of pyridine nucleotide binding and specificity remains an ongoing focus in this field. Therefore, our study aimed to determine the dimerization interface in AspPHBH from Arthrobacter sp. PAMC25564 and identify the canonical pyridine nucleotide-binding residues, along with coenzyme specificity, through site-directed mutagenesis. The results confirm a functional dimeric assembly from a tetramer that appeared in the crystallographic asymmetric unit identical to that established in previous studies. Furthermore, AspPHBH exhibits coenzyme versatility, utilizing both NADH and NADPH, with a preference for NADH. Rational engineering experiments demonstrated that targeted mutations in coenzyme surrounding residues profoundly impact NADPH binding, leading to nearly abrogated enzymatic activity compared to that of NADH. R50, R273, and S166 emerged as significant residues for NAD(P)H binding, having a near-fatal impact on NADPH binding compared to NADH. Likewise, the E44 residue plays a critical role in determining coenzyme specificity. Overall, our findings contribute to the fundamental understanding of the determinants of PHBH's active dimeric conformation, coenzyme binding and specificity holding promise for biotechnological advancements.

Engineering cascade biocatalysis in whole cells for syringic acid bioproduction

BackgroundSyringic acid (SA) is a high-value natural compound with diverse biological activities and wide applications, commonly found in fruits, vegetables, and herbs. SA is primarily produced through chemical synthesis, nonetheless, these chemical methods have many drawbacks, such as considerable equipment requirements, harsh reaction conditions, expensive catalysts, and numerous by-products. Therefore, in this study, a novel biotransformation route for SA production was designed and developed by using engineered whole cells.ResultsAn O-methyltransferase from Desulfuromonas acetoxidans (DesAOMT), which preferentially catalyzes a methyl transfer reaction on the meta-hydroxyl group of catechol analogues, was identified. The whole cells expressing DesAOMT can transform gallic acid (GA) into SA when S-adenosyl methionine (SAM) is used as a methyl donor. We constructed a multi-enzyme cascade reaction in Escherichia coli, containing an endogenous shikimate kinase (AroL) and a chorismate lyase (UbiC), along with a p-hydroxybenzoate hydroxylase mutant (PobA**) from Pseudomonas fluorescens, and DesAOMT; SA was biosynthesized from shikimic acid (SHA) by using whole cells catalysis. The metabolic system of chassis cells also affected the efficiency of SA biosynthesis, blocking the chorismate metabolism pathway improved SA production. When the supply of the cofactor NADPH was optimized, the titer of SA reached 133 μM (26.2 mg/L).ConclusionOverall, we designed a multi-enzyme cascade in E. coli for SA biosynthesis by using resting or growing whole cells. This work identified an O-methyltransferase (DesAOMT), which can catalyze the methylation of GA to produce SA. The multi-enzyme cascade containing four enzymes expressed in an engineered E. coli for synthesizing of SA from SHA. The metabolic system of the strain and biotransformation conditions influenced catalytic efficiency. This study provides a new green route for SA biosynthesis.Graphical

The catabolism of lignin-derived p-methoxylated aromatic compounds by Rhodococcus jostii RHA1.

Emergent strategies to valorize lignin, an abundant but underutilized aromatic biopolymer, include tandem processes that integrate chemical depolymerization and biological catalysis. To date, aromatic monomers from C-O bond cleavage of lignin have been converted to bioproducts, but the presence of recalcitrant C-C bonds in lignin limits the product yield. A promising chemocatalytic strategy that overcomes this limitation involves phenol methyl protection and autoxidation. Incorporating this into a tandem process requires microbial cell factories able to transform the p-methoxylated products in the resulting methylated lignin stream. In this study, we assessed the ability of Rhodococcus jostii RHA1 to catabolize the major aromatic products in a methylated lignin stream and elucidated the pathways responsible for this catabolism. RHA1 grew on a methylated pine lignin stream, catabolizing the major aromatic monomers: p-methoxybenzoate (p-MBA), veratrate, and veratraldehyde. Bioinformatic analyses suggested that a cytochrome P450, PbdA, and its cognate reductase, PbdB, are involved in p-MBA catabolism. Gene deletion studies established that both pbdA and pbdB are essential for growth on p-MBA and several derivatives. Furthermore, a deletion mutant of a candidate p-hydroxybenzoate (p-HBA) hydroxylase, ΔpobA, did not grow on p-HBA. Veratraldehyde and veratrate catabolism required both vanillin dehydrogenase (Vdh) and vanillate O-demethylase (VanAB), revealing previously unknown roles of these enzymes. Finally, a ΔpcaL strain grew on neither p-MBA nor veratrate, indicating they are catabolized through the β-ketoadipate pathway. This study expands our understanding of the bacterial catabolism of aromatic compounds and facilitates the development of biocatalysts for lignin valorization.IMPORTANCELignin, an abundant aromatic polymer found in plant biomass, is a promising renewable replacement for fossil fuels as a feedstock for the chemical industry. Strategies for upgrading lignin include processes that couple the catalytic fractionation of biomass and biocatalytic transformation of the resulting aromatic compounds with a microbial cell factory. Engineering microbial cell factories for this biocatalysis requires characterization of bacterial pathways involved in catabolizing lignin-derived aromatic compounds. This study identifies new pathways for lignin-derived aromatic degradation in Rhodococcus, a genus of bacteria well suited for biocatalysis. Additionally, we describe previously unknown activities of characterized enzymes on lignin-derived compounds, expanding their utility. This work advances the development of strategies to replace fossil fuel-based feedstocks with sustainable alternatives.

Protocatechuate hydroxylase is a novel group A flavoprotein monooxygenase with a unique substrate recognition mechanism

Para-hydroxybenzoate hydroxylase (PHBH) is a group A flavoprotein monooxygenase that hydroxylates p-hydroxybenzoate to protocatechuate (PCA). Despite intensive studies of Pseudomonas aeruginosa p-hydroxybenzoate hydroxylase (PaPobA), the catalytic reactions of extremely diverse putative PHBH isozymes remain unresolved. We analyzed the phylogenetic relationships of known and predicted PHBHs and identified eight divergent clades. Clade F contains a protein that lacks the critical amino acid residues required for PaPobA to generate PHBH activity. Among proteins in this clade, Xylophilus ampelinus PobA (XaPobA) preferred PCA as a substrate and is, the first known natural PCA 5-hydroxylase (PCAH). Crystal structures and kinetic properties revealed similar mechanisms of substrate carboxy group recognition between XaPobA and PaPobA. The unique Ile75, Met72, Val199, Trp201, and Phe385 residues of XaPobA form the bottom of a hydrophobic cavity with a shape that complements the 3-and 4-hydroxy groups of PCA and its binding site configuration. An interaction between the δ-sulfur atom of Met210 and the aromatic ring of PCA is likely to stabilize XaPobA-PCA complexes. The 4-hydroxy group of PCA forms a hydrogen bond with the main chain carbonyl of Thr294. These modes of binding constitute a novel substrate recognition mechanism that PaPobA lacks. This mechanism characterizes XaPobA and sheds light on the diversity of catalytic mechanisms of PobA-type PHBHs and group A flavoprotein monooxygenases.

Bioinduced Surface Oxygen Vacancies on Bismuth Trioxide Nanocrystals for Photocathodic Bioassays

Cathodic photoelectrochemistry with superior photostability and anti-interference capability has been shown to be appealing in the field of bioanalysis. However, a major challenge regarding this technology is the limited photoinduced electron transfer signal transduction mechanism. Herein, we disclose a finding of the bioinduced surface oxygen vacancy (VO) on bismuth trioxide (Bi2O3) nanocrystals, which underlies an innovative mechanism for cathodic photoelectrochemical (PEC) bioanalysis. The protocatechuic acid engendered from the tandem enzymatic reaction of p-hydroxybenzoate hydroxylase (PHBH) and glucose-6-phosphate dehydrogenase (G6PD) can coordinate with the surface of Bi2O3 nanocrystals through forming binary Bi–O–C bonds, which breaks the initial Bi–O bonds and enables the escape of O2– from the lattice to form surface VO in situ. The surface VO can function as a separation center for charge carriers, which is favorable to the generation of cathodic photocurrent. In such a system, the cathodic signal is linearly correlated with the targets, glucose-6-phosphate (G-6-P) and G6PD, in concentration ranges of 8.0 to 8.0 × 105 μM and 0.1 to 1.0 × 104 U/L, achieving detection limits of 2.0 μM and 0.03 U/L, respectively. This study not only offers a way of introducing surface VO in situ but also enriches the current toolbox of cathodic PEC bioassays and promises to stimulate further interest in exploring surface effect engineering in other fields.

Gallic acid fermentation by metabolically engineered Escherichia coli producing p-hydroxybenzoate hydroxylase from Hylemonella gracilis NS1.

Plant-derived phenolic gallic acid (GA) is an important raw material for antioxidants and food additives. Efforts to ferment GA using microbial processes have aimed at minimizing production costs and environmental load using enzymes that hydroxylate p-hydroxybenzoate and protocatechuate (PCA). Here, we found a p-hydroxybenzoate hydroxylase (PobA) in the bacterium Hylemonella gracilis NS1 (HgPobA) with 1.5-fold more hydroxylation activity than that from Pseudomonas aeruginosa PAO1 and thus converted PCA to GA more efficiently. The PCA hydroxylation activity of HgPobA was improved by introducing the amino acid substitutions L207V/Y393F or T302A/Y393F. These mutants had 2.9- and 3.7-fold lower Kmapp for PCA than wild-type HgPobA. An Escherichia coli strain that reinforces shikimate pathway metabolism and produces HgPobA when cultured for 60 h generated 0.27 g L-1 of GA. This is the first report of fermenting glucose to generate GA using a natural enzyme from the PobA family. The E. coli strain harboring the HgPobA L207V/Y393F mutant increased GA production to 0.56 g L-1. During the early stages of culture, GA was fermented at a 10-fold higher rate by a strain producing either HgPobA L207V/Y393F or T302A/Y393F compared with wild-type HgPobA, which agreed with the high kcatapp/Kmapp PCA values of this mutant. We enhanced a PobA isozyme and its PCA hydroxylating function to efficiently and cost-effectively ferment GA.

Description of Pseudogemmobacter faecipullorum sp. nov., isolated from poultry manure.

A polyphasic taxonomic approach was used to characterize a novel bacterium, designated strain CC-YST710T, isolated from poultry manure sampled in Taiwan. Cells of strain CC-YST710T were aerobic, Gram-stain-negative, nonmotile, nonspore-forming rods, displaying positive reactions for catalase, and oxidase activities. Strain CC-YST710T was found to grow optimally at 30°C, pH 7.0, and in the presence of 2% (w/v) NaCl. The polar lipid profile consisted of diphosphatidylglycerol, phosphatidylcholine, phosphatidylglycerol, phosphatidylethanolamine, two unidentified phospholipids, four unidentified aminolipids, one unidentified aminophospholipid, and five unidentified lipids. The major polyamine was spermidine. The dominating cellular fatty acids (> 5%) included C16:0, C18:0, and C18:1ω7c/C18:1ω6c. Based on 16S rRNA gene analysis, this isolate showed the closest phylogenetic relationship with 'Pseudogemmobacter humicola' (97.6%), followed by Pseudogemmobacter bohemicus (97.2%) and 'Pseudogemmobacter hezensis' (97.5%). The draft genome (4.3 Mb) had 62.9 mol% G+C content. CC-YST710T can be distinguished from other Pseudogemmobacter species due to the exclusive presence of key genes encoding p-hydroxybenzoate hydroxylase, protocatechuate 3, 4-dioxygenase (α and β chain), and homogentisate 1, 2-dioxygenase involved in the degradation of phenolic compounds such as p-hydroxybenzoic acid, protocatechuate, and homogentisate, respectively. Orthologous average nucleotide identity (OrthoANI) of the isolate with the type strains of the genera Pseudogemmobacter were 77.6%‒78.0% (n=3), followed by Tabrizicola (72.3%‒73.7%, n=5), and Gemmobacter(72.3%‒73.5%, n=7). Based on its distinct phylogenetic, phenotypic, and chemotaxonomic traits together with results of comparative 16S rRNA gene sequence, OrthoANI, digital DDH, and the phylogenomic placement, strain CC-YST710T is considered to represent a novel Pseudogemmobacter species, for which the name Pseudogemmobacter faecipullorum sp. nov. (type strain CC-YST710T=BCRC 81286T=JCM 34182T).

A high-throughput visual screening method for p-hydroxybenzoate hydroxylase to increase phenolic compounds biosynthesis

BackgroundGallic acid (GA) and pyrogallol are phenolic hydroxyl compounds and have diverse biological activities. Microbial-based biosynthesis, as an ecofriendly method, has been used for GA and pyrogallol production. In GA and pyrogallol biosynthetic pathways, the low hydroxylation activity of p-hydroxybenzoate hydroxylase (PobA) towards 3,4-dihydroxybenzoic acid (3,4-DHBA) limited the high-level biosynthesis of GA and pyrogallol.ResultsThis work reported a high activity PobA mutant (Y385F/T294A/V349A PobA) towards 3,4-DHBA. This mutant was screened out from a PobA random mutagenesis library through a novel naked eye visual screening method. In vitro enzyme assay showed this mutant has a kcat/Km of 0.059 μM−1 s−1 towards 3,4-DHBA, which was 4.92-fold higher than the reported mutant (Y385F/T294A PobA). Molecular docking simulation provided the possible catalytic mechanism explanation of the high activity mutant. Expression of this mutant in E. coli BW25113 (Fʹ) can generate 840 ± 23 mg/L GA from 1000 mg/L 3,4-DHBA. After that, this mutant was assembled into a de novo GA biosynthetic pathway. Subsequently, this pathway was introduced into a 3,4-DHBA-producing strain (E. coli BW25113 (Fʹ)ΔaroE) to achieve 301 ± 15 mg/L GA production from simple carbon sources. Similarly, assembling this mutant into a de novo pyrogallol biosynthetic pathway enabled 129 ± 15 mg/L pyrogallol production.ConclusionsThis work established an efficient screening method and generated a high activity PobA mutant. Assembling this mutant into de novo GA and pyrogallol biosynthetic pathways achieved the production of these two compounds from glucose. Besides, this mutant has great potential for the production of GA or pyrogallol derivatives. The screening method could be used for other GA biosynthesis-related enzymes.

One-Pot Bioconversion of Lignin-Derived Substrates into Gallic Acid.

Lignin is regarded as the most abundant renewable aromatic compound on earth. In this study, we established Escherichia coli-based whole-cell biocatalytic systems to efficiently convert two lignin-derived substrates (ferulic acid and p-coumaric acid) to gallic acid. For the synthesis of gallic acid from ferulic acid, we used the recombinant E. coli expressing feruloyl-CoA synthetase and enoyl-CoA hydratase/aldolase from Pseudomonas putida, aldehyde dehydrogenase (HFD1) from Saccharomyces cerevisiae, vanillic acid O-demethylase (VanAB) from P. putida, and a mutant version of p-hydroxybenzoate hydroxylase (PobAY385F) from P. putida. Under the fed-batch mode, 19.57 mM gallic acid was obtained from 20 mM ferulic acid with a conversion rate of 97.9%. To achieve gallic acid synthesis from p-coumaric acid, we replaced VanAB with the two-component flavin-dependent monooxygenase (HpaBC) from E. coli. Under optimal conditions, 20 mM p-coumaric acid afforded the production of 19.96 mM gallic acid with near 100% conversion. To the best of our knowledge, our work represented the first study to develop E. coli-based whole-cell biocatalysts for the eco-friendly synthesis of gallic acid from lignin-derived renewable feedstocks.

Establishing Interfacial Charge-Transfer Transitions on Ferroelectric Perovskites: An Efficient Route for Photoelectrochemical Bioanalysis

This work presents the concept of establishing interfacial charge-transfer transitions (ICTT) on ferroelectric perovskites for efficient photoelectrochemical (PEC) bioanalysis. The model system was exemplified by using representative lead titanate (PbTiO3) and an enzyme tandem consisting of the isocitrate dehydrogenase (ICDH) and p-hydroxybenzoate hydroxylase (PHBH). The enzymatic generation of protocatechuic acid (PCA) can coordinate onto the surface of the PbTiO3 and hence form the ICTT that enables direct ligand-to-metal charge transfer from the highest occupied molecular orbital (HOMO) of PCA to the conduction band (CB) of PbTiO3 under light irradiation. Due to the ferroelectric polarization induced electric field of PbTiO3 and the surface polarity of PCA modification, enhanced charge separation of the ICTT contributes to the generation of anodic photocurrent and thus underlies a unique route for detecting the enzymatic activity or its substrate. For dehydrogenase detection, this strategy has better performance than some classical methodologies in terms of high sensitivity and improved selectivity. This work not only features ICTT establishment on ferroelectric perovskites for unique bioanalysis but also provides new insights into the utilization of ferroelectric perovskites for advanced PEC bioanalysis.

Coupling p-Hydroxybenzoate Hydroaxylase with the Photoresponsive Nanozyme for Universal Dehydrogenase-Based Bioassays

Herein, an innovative dehydrogenase invoked tri-enzyme cascade has been successfully constructed and utilized as a powerful and universal colorimetric strategy for dehydrogenase-based bioassays. Specifically, the glucose-6-phosphatedehydrogenase (G6PD) catalyzes the specific dehydrogenation of glucose-6-phosphate (G-6-P) by consuming the oxidized form of β-nicotinamide adenine dinucleotide phosphate (NADP+) to generate NADPH. And the formed NADPH initiates the irreversible hydroxylation of p-hydroxybenzoate by p-hydroxybenzoate hydroxylase (PHBH) to generate 3,4-dihydroxybenzoate (DHB), which results in the subsequent in situ generation of a photoresponsive nanozyme of DHB coordinated SrTiO3 (SrTiO3/DHB) nanosheets. The photoresponsive nanozyme has intriguing interfacial charge transfer (ICT) characteristics and thus realizes the efficiently catalytic oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) under light irradiation for signal readout. Exemplified by G6PD and G-6-P as analytes, the dehydrogenase invoked tri-enzyme cascade achieved efficient signal amplification towards the ultrasensitive colorimetric bioassays. This study opens up the ICT transitions of SrTiO3 for innovative dehydrogenases-involved enzyme cascades. In addition, it is an entirely new method for dehydrogenases-based bioassays, with the distinctive merits of facile operation, rapid response, high sensitivity, and naked-eye readout. Importantly, it is extensible as a general basis for other numerous targets of interest because of the large numbers of dehydrogenases available for catalysing different reactions.

Understanding the Molecular Mechanism Underlying the High Catalytic Activity of p-Hydroxybenzoate Hydroxylase Mutants for Producing Gallic Acid.

p-Hydroxybenzoate hydroxylase (PHBH) is a flavoprotein monooxygenase that catalyzes the hydroxylation of p-hydroxybenzoate (p-OHB) to 3,4-dihydroxybenzoate (3,4-DOHB). PHBH can bind to other benzoate derivatives in addition to p-OHB; however, hydroxylation does not occur on 3,4-DOHB. Replacement of Tyr385 with Phe forms a mutant, which enables the production of 3,4,5-trihydroxybenzonate (gallic acid) from 3,4-DOHB, although the catalytic activity of the mutant is quite low. In this study, we report how the L199V/Y385F double mutant exhibits activity for producing gallic acid 4.3-fold higher than that of the Y385F single mutant. This improvement in catalytic activity is primarily due to the suppression of a shunt reaction that wastes reduced nicotinamide adenine dinucleotide phosphate by producing H2O2. To further elucidate the molecular mechanism underlying this higher catalytic activity, we performed molecular dynamics simulations and quantum mechanics/molecular mechanics calculations, in addition to determining the crystal structure of the Y385F·3,4-DOHB complex. The simulations showed that the Y385F mutation facilitates the deprotonation of the 4-hydroxy group of 3,4-DOHB, which is necessary for initiating hydroxylation. Moreover, the L199V mutation in addition to the Y385F mutation allows the OH moiety in the peroxide group of C-(4a)-flavin hydroperoxide to come into the proximity of the C5 atom of 3,4-DOHB. Overall, this study provides a consistent explanation for the change in the catalytic activity of PHBH caused by mutations, which will enable us to better design an enzyme with different activities.

Pyridine Nucleotide Coenzyme Specificity of p-Hydroxybenzoate Hydroxylase and Related Flavoprotein Monooxygenases

p-Hydroxybenzoate hydroxylase (PHBH; EC 1.14.13.2) is a microbial group A flavoprotein monooxygenase that catalyzes the ortho-hydroxylation of 4-hydroxybenzoate to 3,4-dihydroxybenzoate with the stoichiometric consumption of NAD(P)H and oxygen. PHBH and related enzymes lack a canonical NAD(P)H-binding domain and the way they interact with the pyridine nucleotide coenzyme has remained a conundrum. Previously, we identified a surface exposed protein segment of PHBH from Pseudomonas fluorescens involved in NADPH binding. Here, we report the first amino acid sequences of NADH-preferring PHBHs and a phylogenetic analysis of putative PHBHs identified in currently available bacterial genomes. It was found that PHBHs group into three clades consisting of NADPH-specific, NAD(P)H-dependent and NADH-preferring enzymes. The latter proteins frequently occur in Actinobacteria. To validate the results, we produced several putative PHBHs in Escherichia coli and confirmed their predicted coenzyme preferences. Based on phylogeny, protein energy profiling and lifestyle of PHBH harboring bacteria we propose that the pyridine nucleotide coenzyme specificity of PHBH emerged through adaptive evolution and that the NADH-preferring enzymes are the older versions of PHBH. Structural comparison and distance tree analysis of group A flavoprotein monooxygenases indicated that a similar protein segment as being responsible for the pyridine nucleotide coenzyme specificity of PHBH is involved in determining the pyridine nucleotide coenzyme specificity of the other group A members.

Toward Accurate QM/MM Reaction Barriers with Large QM Regions Using Domain Based Pair Natural Orbital Coupled Cluster Theory.

The hydroxylation reaction catalyzed by p-hydroxybenzoate hydroxylase and the Baeyer-Villiger reaction catalyzed by cyclohexanone monooxygenase are investigated by means of quantum mechanical/molecular mechanical (QM/MM) calculations at different levels of QM theory. The geometries of the stationary points along the reaction profile are obtained from QM/MM geometry optimizations, in which the QM region is treated by density functional theory (DFT). Relative energies are determined from single-point QM/MM calculations using the domain-based local pair natural orbital coupled cluster DLPNO-CCSD(T) method as QM component. The results are compared with single-point DFT/MM energies obtained using popular density functionals and with available experimental and computational data. It is found that the choice of the QM method strongly affects the computed energy profiles for these reactions. Different density functionals provide qualitatively different energy barriers (variations of the order of 10 kcal/mol in both reactions), thus limiting the confidence in DFT/MM computational predictions of energy profiles. On the other hand, the use of the DLPNO-CCSD(T) method in conjunction with large QM regions and basis sets makes it possible to achieve high accuracy. A critical discussion of all the technical aspects of the calculations is given with the aim of aiding computational chemists in the application of the DLPNO-CCSD(T) methodology in QM/MM calculations.

Structural Basis for Inhibitor-Induced Hydrogen Peroxide Production by Kynurenine 3-Monooxygenase

Kynurenine 3-monooxygenase (KMO) inhibitors have been developed for the treatment of neurodegenerative disorders. The mechanisms of flavin reduction and hydrogen peroxide production by KMO inhibitors are unknown. Herein, we report the structure of human KMO and crystal structures of Saccharomyces cerevisiae (sc) and Pseudomonas fluorescens(pf) KMO with Ro 61-8048. Proton transfer in the hydrogen bond network triggers flavin reduction in p-hydroxybenzoate hydroxylase, but the mechanism triggering flavin reduction in KMO is different. Conformational changes via π-π interactions between the loop above the flavin and substrate or non-substrate effectors lead to disorder of the C-terminal α helix in scKMO and shifts of domain III in pfKMO, stimulating flavin reduction. Interestingly, Ro 61-8048 has two different binding modes. It actsas a competitive inhibitor in scKMO and as anon-substrate effector in pfKMO. These findings provide understanding of the catalytic cycle of KMO and insight for structure-based drug design of KMO inhibitors.

Rational engineering of p-hydroxybenzoate hydroxylase to enable efficient gallic acid synthesis via a novel artificial biosynthetic pathway.

Gallic acid (GA) is a naturally occurring phytochemical that has strong antioxidant and antibacterial activities. It is also used as a potential platform chemical for the synthesis of diverse high-value compounds. Hydrolytic degradation of tannins by acids, bases or microorganisms serves as a major way for GA production, which however, might cause environmental pollution and low yield and efficiency. Here, we report a novel approach for efficient microbial production of GA. First, structure-based rational engineering of PobA, a p-hydroxybenzoate hydroxylase from Pseudomonas aeruginosa, generated a new mutant, Y385F/T294A PobA, which displayed much higher activity toward 3,4-dihydroxybenzoic acid (3,4-DHBA) than the wild-type and any other reported mutants. Remarkably, expression of this mutant in Escherichia coli enabled generation of 1149.59 mg/L GA from 1000 mg/L 4-hydroxybenzoic acid (4-HBA), representing a 93% molar conversion ratio. Based on that, we designed and reconstituted a novel artificial biosynthetic pathway of GA and achieved 440.53 mg/L GA production from simple carbon sources in E. coli. Further enhancement of precursor supply through reinforcing shikimate pathway was able to improve GA de novo production to 1266.39 mg/L in shake flasks. Overall, this study not only led to the development of a highly active PobA variant for hydroxylating 3,4-DHBA into GA via structure-based protein engineering approach, but also demonstrated a promising pathway for bio-based manufacturing of GA and its derived compounds. Biotechnol. Bioeng. 2017;114: 2571-2580. © 2017 Wiley Periodicals, Inc.

Establishing an Artificial Pathway for De Novo Biosynthesis of Vanillyl Alcohol in Escherichia coli

Vanillyl alcohol is a phenolic alcohol and is used as a flavoring agent in foods and beverages. In this paper, we propose a novel artificial pathway for microbial production of vanillyl alcohol from simple carbon sources. The pathway extends from 4-hydroxybenzoic acid (4-HBA), and needs only three heterologous enzymes, p-hydroxybenzoate hydroxylase (PobA), carboxylic acid reductase (CAR) and caffeate O-methyltransferase (COMT). First, we examined the promiscuous activity of COMT toward 3,4-dihydroxybenzyl alcohol and found a kcat value of 0.097 s-1. Meanwhile, 499.36 mg/L vanillyl alcohol was produced by COMT in vivo catalysis when fed with 1000 mg/L 3,4-dihydroxybenzyl alcohol. In the following experiment, de novo biosynthesis of vanillyl alcohol was carried out and 240.69 mg/L vanillyl alcohol was produced via modular optimization of pathway genes. This work was to date the first achievement for microbial production of vanillyl alcohol. Additionally, the present study demonstrates the application of enzyme promiscuity of COMT in the design of an artificial pathway for the production of high-value methylated aromatic compounds.

Importance of MM Polarization in QM/MM Studies of Enzymatic Reactions: Assessment of the QM/MM Drude Oscillator Model.

Comput. 2014, 10, 1795-1809), we now report a comprehensive investigation of the effects of MM polarization on two enzymatic reactions, namely the Claisen rearrangement in chorismate mutase and the hydroxylation reaction in p-hydroxybenzoate hydroxylase, using the QM/CHARMM-DO model and two QM methods (B3LYP, OM2). We compare the results from extensive geometry optimizations and free energy simulations at the QM/MM-DO level to those obtained from analogous calculations at the conventional QM/MM level.

Benzimidazoles as competitive inhibitors of FAD-monooxygenase

Benzimidazoles are drugs which target tubulin and are widely used to treat intestinal parasites. Four benzimidazoles are tested with the well-characterized and commercially available bacterial p-hydroxybenzoate hydroxylase (PHBH), which belongs to the group of Class A FAD-monooxygenases, which also includes such enzymes as the FAD-monooxygenase domain of MICAL. PHBH is shown to be competitively inhibited by all four benzimidazoles (mebendazole, albendazole, fenbendazole, and oxibendazole) in the micromolar range in the hydroxylase reaction, but not in the non-physiological NADPH-dehydrogenase reaction of ferricyanide reduction. The inhibition pattern is consistent with benzimidazoles competing with p-hydroxybenzoate for the resting state of the enzyme, indirectly indicating the ordered mechanism of substrate binding. Modeling studies support the conclusions derived from steady-state kinetics.

Identification of Putative Genes Involved in Bisphenol A Degradation Using Differential Protein Abundance Analysis of Sphingobium sp. BiD32.

Discharge of the endocrine disrupting compound bisphenol A (BPA) with wastewater treatment plant (WWTP) effluents into surface waters results in deleterious effects on aquatic life. Sphingobium sp. BiD32 was previously isolated from activated sludge based on its ability to degrade BPA. This study investigated BPA metabolism by Sphingobium sp. BiD32 using label-free quantitative proteomics. The genome of Sphingobium sp. BiD32 was sequenced to provide a species-specific platform for optimal protein identification. The bacterial proteomes of Sphingobium sp. BiD32 in the presence and absence of BPA were identified and quantified. A total of 2155 proteins were identified; 1174 of these proteins were quantified, and 184 of these proteins had a statistically significant change in abundance in response to the presence/absence of BPA (p ≤ 0.05). Proteins encoded by genes previously identified to be responsible for protocatechuate degradation were upregulated in the presence of BPA. The analysis of the metabolites from BPA degradation by Sphingobium sp. BiD32 detected a hydroxylated metabolite. A novel p-hydroxybenzoate hydroxylase enzyme detected by proteomics was implicated in the metabolic pathway associated with the detected metabolite. This enzyme is hypothesized to be involved in BPA degradation by Sphingobium sp. BiD32, and may serve as a future genetic marker for BPA degradation.