Hydroxylation of flavanones by cytochrome P450 105D7 from Streptomyces avermitilis

Potential of Streptomyces avermitilis: A Review on Avermectin Production and Its Biocidal Effect

Secondary metabolites produced by the fermentation of Streptomyces avermitilis bacterium are powerful antiparasitic agents used in animal health, agriculture and human infection treatments. Avermectin is a macrocyclic lactone with four structural components (A1, A2, B1, B2), each of them containing a major and a minor subcomponent, out of which avermectin B1a is the most effective parasitic control compound. Avermectin B1a produces two homologue avermectins (B1 and B2) that have been used in agriculture as pesticides and antiparasitic agents, since 1985. It has a great affinity with the Cl-channels of the glutamate receptor, allowing the constant flow of Cl- ions into the nerve cells, causing a phenomenon of hyperpolarization causing death by flaccid paralysis. The purpose of this work was to gather information on the production of avermectins and their biocidal effects, with special emphasis on their role in the control of pests and phytopathogenic diseases. The literature showed that S. avermitilis is an important producer of macrocyclic lactones with biocidal properties. In addition, avermectin contributes to the control of ectoparasites and endoparasites in human health care, veterinary medicine and agriculture. Importantly, avermectin is a compound that is harmless to the host (no side effects), non-target organisms and the environment.

Microbial P450 repertoire (P450ome) and its application feasibility in pharmaceutical industry, chemical industry, and environmental protection

Cytochrome P450s (CYPs) are heme-thiolated enzymes that catalyze the oxidation of C-H bonds in a regio- and stereo-selective manner. CYPs are widely present in the biological world. With the completion of more biological genome sequencing, the number and types of P450 enzymes have increased rapidly. P450 in microorganisms is easy to clone and express, rich in catalytic types, and strong in substrate adaptability, which has good application potential. Although the number of P450 enzymes found in microorganisms is huge, the function of most of the microorganism P450s has not been studied, and it contains a large number of excellent biocatalysts to be developed. This review is based on the P450 groups in microorganisms. First, it reviews the distribution of P450 groups in different microbial species, and then studies the application of microbial P450 enzymes in the pharmaceutical industry, chemical industry and environmental pollutant treatment in recent years. And focused on the application fields of P450 enzymes of different families to guide the selection of suitable P450s from the huge P450 library. In view of the current shortcomings of microbial P450 in the application process, the final solution is the most likely to assist the application of P450 enzymes in large-scale, that is, whole cell transformation combined with engineering, fusion P450 combined with immobilization technology.

Efficient hydroxylation of flavonoids by using whole-cell P450 sca-2 biocatalyst in Escherichia coli

The hydroxylation is an important way to generate the functionalized derivatives of flavonoids. However, the efficient hydroxylation of flavonoids by bacterial P450 enzymes is rarely reported. Here, a bacterial P450 sca-2_mut whole-cell biocatalyst with an outstanding 3'-hydroxylation activity for the efficient hydroxylation of a variety of flavonoids was first reported. The whole-cell activity of sca-2_mut was enhanced using a novel combination of flavodoxin Fld and flavodoxin reductase Fpr from Escherichia coli. In addition, the double mutant of sca-2_mut (R88A/S96A) exhibited an improved hydroxylation performance for flavonoids through the enzymatic engineering. Moreover, the whole-cell activity of sca-2_mut (R88A/S96A) was further enhanced by the optimization of whole-cell biocatalytic conditions. Finally, eriodictyol, dihydroquercetin, luteolin, and 7,3',4'-trihydroxyisoflavone, as examples of flavanone, flavanonol, flavone, and isoflavone, were produced by whole-cell biocatalysis using naringenin, dihydrokaempferol, apigenin, and daidzein as the substrates, with the conversion yield of 77%, 66%, 32%, and 75%, respectively. The strategy used in this study provided an effective method for the further hydroxylation of other high value-added compounds.

Crystal Structure and Biochemical Analysis of a Cytochrome P450 CYP101D5 from Sphingomonas echinoides

Cytochrome P450 enzymes (CYPs) are heme-containing enzymes that catalyze hydroxylation with a variety of biological molecules. Despite their diverse activity and substrates, the structures of CYPs are limited to a tertiary structure that is similar across all the enzymes. It has been presumed that CYPs overcome substrate selectivity with highly flexible loops and divergent sequences around the substrate entrance region. Here, we report the newly identified CYP101D5 from Sphingomonas echinoides. CYP101D5 catalyzes the hydroxylation of β-ionone and flavonoids, including naringenin and apigenin, and causes the dehydrogenation of α-ionone. A structural investigation and comparison with other CYP101 families indicated that spatial constraints at the substrate-recognition site originate from the B/C loop. Furthermore, charge distribution at the substrate binding site may be important for substrate selectivity and the preference for CYP101D5.

Engineering of Microbial Substrate Promiscuous CYP105A5 for Improving the Flavonoid Hydroxylation

Bacterial cytochrome P450 (CYP) enzymes are versatile biocatalysts that are responsible for the biotransformation of diverse endogenous substances. CYP105A5 from Streptomyces sp. showed substrate flexibility with different flavonoids and was able to catalyze O-demethylation of biochanin A, regioselective C3′-hydroxylation of daidzein, genistein, and naringenin, and additional C8-hydroxylation for daidzein using heterologous redox partners putidaredoxin and putidaredoxin reductase. By rational design of substrate-binding pocket based on experimental data, homology modeling, and molecular docking analysis, we enhanced the product formation rate of flavonoids. The double mutant L100A/I302A and L100A/I408N exhibited greatly enhanced in vivo conversion rates for flavonoid hydroxylation. Particularly, the L100A/I302A mutant’s kcat/Km values and in vivo conversion rate increased by 1.68-fold and 2.57-fold, respectively, for naringenin. Overall, our result might facilitate the potential use of CYP105A5 for future modification and application in whole-cell biocatalysts for the production of valuable polyphenols.

Hydroxylation, Epoxidation, and Dehydrogenation of Capsaicin by a Microbial Promiscuous Cytochrome P450 105D7

Cytochrome P450 enzymes (P450s) are versatile biocatalysts, which insert a molecular oxygen into inactivated C-H bonds under mild conditions. CYP105D7 from Streptomyces avermitilis has been reported as a bacterial substrate-promiscuous P450 which catalyzes the hydroxylation of 1-deoxypentalenic acid, diclofenac, naringenin, compactin and steroids. In this study, CYP105D7 catalyzes hydroxylation, epoxidation and dehydrogenation of capsaicin, a pharmaceutical agent, revealing its functional diversity. The kinetic parameters of the CYP105D7 oxidation of capsaicin were determined as K_m =311.60±87.30 μM and k_cat =2.01±0.33 min^-1 . In addition, we conducted molecular docking, mutagenesis and substrate binding analysis, indicating that Arg81 plays crucial role in the capsaicin binding and catalysis. To our best knowledge, this study presents the first report to illustrate that capsaicin can be catalyzed by prokaryotic P450s.

Naturally Occurring Flavonoids and Isoflavonoids and Their Microbial Transformation: A Review

Flavonoids and isoflavonoids are polyphenolic secondary metabolites usually produced by plants adapting to changing ecological environments over a long period of time. Therefore, their biosynthesis pathways are considered as the most distinctive natural product pathway in plants. Seemingly, the flavonoids and isoflavones from fungi and actinomycetes have been relatively overlooked. In this review, we summarized and classified the isoflavones and flavonoids derived from fungi and actinomycetes and described their biological activities. Increasing attention has been paid to bioactive substances derived from microorganism whole-cell biotransformation. Additionally, we described the utilization of isoflavones and flavonoids as substrates by fungi and actinomycetes for biotransformation through hydroxylation, methylation, halogenation, glycosylation, dehydrogenation, cyclisation, and hydrogenation reactions to obtain rare and highly active biofunctional derivatives. Overall, among all microorganisms, actinomycetes are the main producers of flavonoids. In our review, we also summarized the functional genes involved in flavonoid biosynthesis.

Hydroxylation of Steroids by a Microbial Substrate-Promiscuous P450 Cytochrome (CYP105D7): Key Arginine Residues for Rational Design

Our previous study showed that CYP105D7, a substrate-promiscuous P450, catalyzes the hydroxylation of 1-deoxypentalenic acid, diclofenac, naringenin, and compactin. In this study, 14 steroid compounds were screened using recombinant Escherichia coli cells harboring genes encoding CYP105D7 and redox partners (Pdx/Pdr, RhFRED, and FdxH/FprD), and the screening identified steroid A-ring 2β- and D-ring 16β-hydroxylation activity. Wild-type CYP105D7 was able to catalyze the hydroxylation of five steroids (testosterone, progesterone, 4-androstene-3,17-dione, adrenosterone, and cortisone) with low (<10%) conversion rates. Structure-guided site-directed mutagenesis of arginine residues around the substrate entrance and active site showed that the R70A and R190A single mutants and an R70A/R190A double mutant exhibited greatly enhanced conversion rates for steroid hydroxylation. For the conversion of testosterone in particular, the R70A/R190A mutant's k _cat/K_m values increased 1.35-fold and the in vivo conversion rates increased significantly by almost 9-fold with high regio- and stereoselectivity. Molecular docking analysis revealed that when Arg70 and Arg190 were replaced with alanine, the volume of the substrate access and binding pocket increased 1.08-fold, which might facilitate improvement of the hydroxylation efficiency of steroids.IMPORTANCE Cytochrome P450 monooxygenases (P450s) are able to introduce oxygen atoms into nonreactive hydrocarbon compounds under mild conditions, thereby offering significant advantages compared to chemical catalysts. Promiscuous P450s with broad substrate specificity and reaction diversity have significant potential for applications in various fields, including synthetic biology. The study of the function, molecular mechanisms, and rational engineering of substrate-promiscuous P450s from microbial sources is important to fulfill this potential. Here, we present a microbial substrate-promiscuous P450, CYP105D7, which can catalyze hydroxylation of steroids. The loss of the bulky side chains of Arg70 and Arg190 in the active site and substrate entrance resulted in an up to 9-fold increase in the substrate conversion rate. These findings will support future rational and semirational engineering of P450s for applications as biocatalysts.

Rational and semi-rational engineering of cytochrome P450s for biotechnological applications

The cytochrome P450 enzymes are ubiquitous heme-thiolate proteins performing regioselective and stereoselective oxygenation reactions in cellular metabolism. Due to their broad substrate scope and catalytic versatility, P450 enzymes are also attractive candidates for many industrial and biopharmaceutical applications. For particular uses, enzyme properties of P450s can be further optimized through directed evolution, rational, and semi-rational engineering approaches, all of which introduce mutations within the P450 structures. In this review, we describe the recent applications of these P450 engineering approaches and highlight the key regions and residues that have been identified using such approaches. These “hotspots” lie within critical functional areas of the P450 structure, including the active site, the substrate access channel, and the redox partner interaction interface.

Structural insights into oxidation of medium-chain fatty acids and flavanone by myxobacterial cytochrome P450 CYP267B1

Oxidative biocatalytic reactions performed by cytochrome P450 enzymes (P450s) are of high interest for the chemical and pharmaceutical industries. CYP267B1 is a P450 enzyme from myxobacterium Sorangium cellulosum So ce56 displaying a broad substrate scope. In this work, a search for new substrates was performed, combined with product characterization and a structural analysis of substrate-bound complexes using X-ray crystallography and computational docking. The results demonstrate the ability of CYP267B1 to perform in-chain hydroxylations of medium-chain saturated fatty acids (decanoic acid, dodecanoic acid and tetradecanoic acid) and a regioselective hydroxylation of flavanone. The fatty acids are mono-hydroxylated at different in-chain positions, with decanoic acid displaying the highest regioselectivity towards ω-3 hydroxylation. Flavanone is preferably oxidized to 3-hydroxyflavanone. High-resolution crystal structures of CYP267B1 revealed a very spacious active site pocket, similarly to other P450s capable of converting macrocyclic compounds. The pocket becomes more constricted near to the heme and is closed off from solvent by residues of the F and G helices and the B-C loop. The crystal structure of the tetradecanoic acid-bound complex displays the fatty acid bound near to the heme, but in a nonproductive conformation. Molecular docking allowed modeling of the productive binding modes for the four investigated fatty acids and flavanone, as well as of two substrates identified in a previous study (diclofenac and ibuprofen), explaining the observed product profiles. The obtained structures of CYP267B1 thus serve as a valuable prediction tool for substrate hydroxylations by this highly versatile enzyme and will encourage future selectivity changes by rational protein engineering.

Cytochromes P450 for natural product biosynthesis in Streptomyces: sequence, structure, and function

Covering: up to January 2017Cytochrome P450 enzymes (P450s) are some of the most exquisite and versatile biocatalysts found in nature. In addition to their well-known roles in steroid biosynthesis and drug metabolism in humans, P450s are key players in natural product biosynthetic pathways. Natural products, the most chemically and structurally diverse small molecules known, require an extensive collection of P450s to accept and functionalize their unique scaffolds. In this review, we survey the current catalytic landscape of P450s within the Streptomyces genus, one of the most prolific producers of natural products, and comprehensively summarize the functionally characterized P450s from Streptomyces. A sequence similarity network of >8500 P450s revealed insights into the sequence-function relationships of these oxygen-dependent metalloenzymes. Although only ∼2.4% and <0.4% of streptomycete P450s have been functionally and structurally characterized, respectively, the study of streptomycete P450s involved in the biosynthesis of natural products has revealed their diverse roles in nature, expanded their catalytic repertoire, created structural and mechanistic paradigms, and exposed their potential for biomedical and biotechnological applications. Continued study of these remarkable enzymes will undoubtedly expose their true complement of chemical and biological capabilities.

Protein engineering of CYP105s for their industrial uses

Cytochrome P450 enzymes belonging to the CYP105 family are predominantly found in bacteria belonging to the phylum Actinobacteria and the order Actinomycetales. In this review, we focused on the protein engineering of P450s belonging to the CYP105 family for industrial use. Two Arg substitutions to Ala of CYP105A1 enhanced its vitamin D₃ 25- and 1α-hydroxylation activities by 400 and 100-fold, respectively. The coupling efficiency between product formation and NADPH oxidation was largely improved by the R84A mutation. The quintuple mutant Q87W/T115A/H132L/R194W/G294D of CYP105AB3 showed a 20-fold higher activity than the wild-type enzyme. Amino acids at positions 87 and 191 were located at the substrate entrance channel, and that at position 294 was located close to the heme group. Semi-rational engineering of CYP105A3 selected the best performing mutant, T85F/T119S/V194N/N363Y, for producing pravastatin. The T119S and N363Y mutations synergistically had remarkable effects on the interaction between CYP105A3 and putidaredoxin. Although wild-type CYP105AS1 hydroxylated compactin to 6-epi-pravastatin, the quintuple mutant I95T/Q127R/A180V/L236I/A265N converted almost all compactin to pravastatin. Five amino acid substitutions by two rounds of mutagenesis almost completely changed the stereo-selectivity of CYP105AS1. These results strongly suggest that the protein engineering of CYP105 enzymes greatly increase their industrial utility. This article is part of a Special Issue entitled: Cytochrome P450 biodiversity and biotechnology, edited by Erika Plettner, Gianfranco Gilardi, Luet Wong, Vlada Urlacher, Jared Goldstone.