Sam5, a Coumarate 3-Hydroxylase fromSaccharothrix espanaensis: New Insight into the Piceatannol Production as a Resveratrol 3’-Hydroxylase

Modification of the 4-Hydroxyphenylacetate-3-hydroxylase Substrate Pocket to Increase Activity towards Resveratrol

4-Hydroxyphenylacetate-3-hydroxylase (4HPA3H; EC 1.14.14.9) is a heterodimeric flavin-dependent monooxygenase complex that catalyzes the ortho-hydroxylation of resveratrol to produce piceatannol. Piceatannol has various health benefits and valuable applications in food, medicine, and cosmetics. Enhancing the catalytic activity of 4HPA3H toward resveratrol has the potential to benefit piceatannol production. In this study, the critical amino acid residues in the substrate pocket of 4HPA3H that affect its activity toward resveratrol were identified using semi-rational engineering. Two key amino acid sites (I157 and A211) were discovered and the simultaneous "best" mutant I157L/A211D enabled catalytic efficiency (Kcat/Km-resveratrol) to increase by a factor of 4.7-fold. Molecular dynamics simulations indicated that the increased flexibility of the 4HPA3H substrate pocket has the potential to improve the catalytic activity of the enzyme toward resveratrol. On this basis, we produced 3.78 mM piceatannol by using the mutant I157L/A211D whole cells. In this study, we successfully developed a highly active 4HPA3H variant for the hydroxylation of resveratrol to piceatannol.

Phenolic hydroxylases

Many flavin-dependent phenolic hydroxylases (monooxygenases) have been extensively investigated. Their crystal structures and reaction mechanisms are well understood. These enzymes belong to groups A and D of the flavin-dependent monooxygenases and can be classified as single-component and two-component flavin-dependent monooxygenases. The insertion of molecular oxygen into the substrates catalyzed by these enzymes is beneficial for modifying the biological properties of phenolic compounds and their derivatives. This chapter provides an in-depth discussion of the structural features of single-component and two-component flavin-dependent phenolic hydroxylases. The reaction mechanisms of selected enzymes, including 3-hydroxy-benzoate 4-hydroxylase (PHBH) and 3-hydroxy-benzoate 6-hydroxylase as representatives of single-component enzymes and 3-hydroxyphenylacetate 4-hydroxylase (HPAH) as a representative of two-component enzymes, are discussed in detail. This chapter comprises the following four main parts: general reaction, structures, reaction mechanisms, and enzyme engineering for biocatalytic applications. Enzymes belonging to the same group catalyze similar reactions but have different unique structural features to control their reactivity to substrates and the formation and stabilization of C4a-hydroperoxyflavin. Protein engineering has been employed to improve the ability to use these enzymes to synthesize valuable compounds. A thorough understanding of the structural and mechanistic features controlling enzyme reactivity is useful for enzyme redesign and enzyme engineering for future biocatalytic applications.

Characteristics, Biological Properties and Analytical Methods of Trans-Resveratrol: A Review

Trans-resveratrol (TR) is the biological active isomer of resveratrol and the one responsible for therapeutic effects; both molecules are non-flavonoid phenolics of the stilbenes class found mainly in berries and red grapes. TR biological properties lie in modulation of various enzymatic classes. It is a promising candidate to novel drugs due its applications in pharmaceutical and cosmetic industries, such as anticarcinogenic, antidiabetic, antiacne, antioxidant, anti-inflammatory, neuroprotective, and photoprotector agent. It has effects on bone metabolism, gastrointestinal tract, eyes, kidneys, and in obesity treatment as well. Nevertheless, its low solubility in water and other polar solvents may be a hindrance to its therapeutic effects. Various strategies been developed to overcome these issues, such as the drug delivery systems. The present study performed a research about methods to identify TR and RESV in several samples (raw materials, wines, food supplements, drug delivery systems, and blood plasma). Most of the studies tend to analyze TR and RESV by high performance liquid chromatography (HPLC) coupled with different detectors, even so, there are reports of the use of capillary electrophoresis, electron spin resonance, gas chromatography, near-infrared luminescence, UV-Vis spectrophotometer, and vibrational spectrophotometry, for this purpose. Thus, the review evaluates the biological activity of TR and demonstrates the currently used analytical methods for its quantification in different matrices.

Isolation and characterization of Gram-negative and Gram-positive bacteria capable of producing piceatannol from resveratrol

Piceatannol is a valuable natural polyphenol with therapeutic potential in cardiovascular and metabolic disease treatment. In this study, we screened for microorganisms capable of producing piceatannol from resveratrol via regioselective hydroxylation. In the first screening, we isolated microorganisms utilizing resveratrol, phenol, or 4-hydroxyphenylacetic acid as a carbon source for growth. In the second screening, we assayed the isolated microorganisms for hydroxylation of resveratrol. Using this screening procedure, a variety of resveratrol-converting microorganisms were obtained. One Gram-negative bacterium, Ensifer sp. KSH1, and one Gram-positive bacterium, Arthrobacter sp. KSH3, utilized 4-hydroxyphenylacetic acid as a carbon source for growth and efficiently hydroxylated resveratrol to piceatannol without producing any detectable by-products. The hydroxylation activity of strains KSH1 and KSH3 was strongly induced by cultivation with 4-hydroxyphenylacetic acid as a carbon source during stationary growth phase. Using the 4-hydroxyphenylacetic acid-induced cells as a biocatalyst under optimal conditions, production of piceatannol by strains KSH1 and KSH3 reached 3.6 mM (0.88 g/L) and 2.6 mM (0.64 g/L), respectively. We also cloned genes homologous to the monooxygenase gene hpaBC from strains KSH1 and KSH3. Introduction of either hpaBC homolog into Escherichia coli endowed the host with resveratrol-hydroxylating activity.

A comparison between the homocyclic aromatic metabolic pathways from plant-derived compounds by bacteria and fungi

Aromatic compounds derived from lignin are of great interest for renewable biotechnical applications. They can serve in many industries e.g. as biochemical building blocks for bioplastics or biofuels, or as antioxidants, flavor agents or food preservatives. In nature, lignin is degraded by microorganisms, which results in the release of homocyclic aromatic compounds. Homocyclic aromatic compounds can also be linked to polysaccharides, tannins and even found freely in plant biomass. As these compounds are often toxic to microbes already at low concentrations, they need to be degraded or converted to less toxic forms. Prior to ring cleavage, the plant- and lignin-derived aromatic compounds are converted to seven central ring-fission intermediates, i.e. catechol, protocatechuic acid, hydroxyquinol, hydroquinone, gentisic acid, gallic acid and pyrogallol through complex aromatic metabolic pathways and used as energy source in the tricarboxylic acid cycle. Over the decades, bacterial aromatic metabolism has been described in great detail. However, the studies on fungal aromatic pathways are scattered over different pathways and species, complicating a comprehensive view of fungal aromatic metabolism. In this review, we depicted the similarities and differences of the reported aromatic metabolic pathways in fungi and bacteria. Although both microorganisms share the main conversion routes, many alternative pathways are observed in fungi. Understanding the microbial aromatic metabolic pathways could lead to metabolic engineering for strain improvement and promote valorization of lignin and related aromatic compounds.

Modular pathway engineering for resveratrol and piceatannol production in engineered Escherichia coli

Resveratrol and its ortho-hydroxylated derivative piceatannol were biosynthesized by modular pathway engineering in Escherichia coli. The biosynthetic pathway was divided into three different modules. Module I includes polyketide biosynthetic genes; module II genes include acetyl-CoA and malonyl-CoA pool-enhancing genes from three different organisms; and module III genes are regiospecific 3'-hydroxylating enzymes. E. coli BL21(DE3) with module I produced 8.6 mg/L of resveratrol from exogenously fed 1 mM p-coumaric acid after 72 h. Combination of module I and acetyl-CoA supplementing module IIb genes from N. farcinica IFM10152 produced 2.5-fold higher (60 mg/L) titer of resveratrol than the module IIa genes from E. coli. The exogenous supplementation of sodium acetate further enhanced production to 64 mg/L. Furthermore, module I with module IIc harboring matBC from S. coelicolor A3(2) produced 73 mg/L of resveratrol, which was elevated to 151 mg/L upon supplementing disodium malonate exogenously. This increment is 17.5-fold higher than module I harboring E. coli BL21(DE3). The combination of module I and two different module II genes yielded 137 mg/L resveratrol when supplemented with both sodium acetate and disodium malonate. The high resveratrol-producing combination module was further modified with incorporation of hpaBC for the ortho-hydroxylation of resveratrol to produce piceatannol. The engineered strain harboring modules I, IIc and III produced 124 mg/L of piceatannol, the highest titer after 72 h in disodium malonate-supplemented strain, which is 2-fold higher than in non-supplemented strain. The remaining resveratrol was about 30 mg/L. Furthermore, caffeic acid (85.5 mg/L) was also produced in the same strain. Resveratrol and piceatannol were biosynthesized along with caffeic acid by three different modules overexpressing acetate and malonate assimilation pathway genes from three different sources. The production titer of both resveratrol and piceatannol could be achieved higher upon blocking acetyl-CoA and malonyl-CoA utilizing pathway genes in host strain.