Fungal BVMOs as alternatives to cyclohexanone monooxygenase

Bicyclo[3.2.0]carbocyclic Molecules and Redox Biotransformations: The Evolution of Closed-Loop Artificial Linear Biocatalytic Cascades and Related Redox-Neutral Systems

The role of cofactor recycling in determining the efficiency of artificial biocatalytic cascades has become paramount in recent years. Closed-loop cofactor recycling, which initially emerged in the 1990s, has made a valuable contribution to the development of this aspect of biotechnology. However, the evolution of redox-neutral closed-loop cofactor recycling has a longer history that has been integrally linked to the enzymology of oxy-functionalised bicyclo[3.2.0]carbocyclic molecule metabolism throughout. This review traces that relevant history from the mid-1960s to current times.

Multienzymatic Processes Involving Baeyer–Villiger Monooxygenases

Baeyer–Villiger monooxygenases (BVMOs) are flavin-dependent oxidative enzymes capable of catalyzing the insertion of an oxygen atom between a carbonylic Csp2 and the Csp3 at the alpha position, therefore transforming linear and cyclic ketones into esters and lactones. These enzymes are dependent on nicotinamides (NAD(P)H) for the flavin reduction and subsequent reaction with molecular oxygen. BVMOs can be included in cascade reactions, coupled to other redox enzymes, such as alcohol dehydrogenases (ADHs) or ene-reductases (EREDs), so that the direct conversion of alcohols or α,β-unsaturated carbonylic compounds to the corresponding esters can be achieved. In the present review, the different synthetic methodologies that have been performed by employing multienzymatic strategies with BVMOs combining whole cells or isolated enzymes, through sequential or parallel methods, are described, with the aim of highlighting the advantages of performing multienzymatic systems, and show the recent advances for overcoming the drawbacks of using BVMOs in these techniques.

Optimizing the linker length for fusing an alcohol dehydrogenase with a cyclohexanone monooxygenase

The use of enzymes in organic synthesis is highly appealing due their remarkably high chemo-, regio- and enantioselectivity. Nevertheless, for biosynthetic routes to be industrially useful, the enzymes must fulfill several requirements. Particularly, in case of cofactor-dependent enzymes self-sufficient systems are highly valuable. This can be achieved by fusing enzymes with complementary cofactor dependency. Such bifunctional enzymes are also relatively easy to handle, may enhance stability, and promote product intermediate channeling. However, usually the characteristics of the linker, fusing the target enzymes, are not thoroughly evaluated. A poor linker design can lead to detrimental effects on expression levels, enzyme stability and/or enzyme performance. In this chapter, the effect of the length of a glycine-rich linker was explored for the case study of ɛ-caprolactone synthesis through an alcohol dehydrogenase-cyclohexanone monooxygenase fusion system. The procedure includes cloning of linker variants, expression analysis, determination of thermostability and effect on activity and conversion levels of 15 variants of different linker sizes. The protocols can also be used for the creation of other protein-protein fusions.

Biocatalytic production of Ɛ-caprolactone using Geotrichum candidum cells immobilized on functionalized silica

Immobilization of the Geotrichum candidum (CCT 1205) cell with functionalized silica creates promising biocatalysts for production of ɛ-caprolactone. The results obtained by immobilization of the whole cell on SiO₂-NH₂ and SiO₂-SH supports indicate that the presence of reactive functional groups on the support may promote effective chemical bonds with the cell walls resulting the decreased dehydrogenases enzyme activity (5% yield in less than 2h) and consequently, increased Baeyer-Villiger monooxygenases enzyme activity with redacting of 25% of time reaction when is used SiO₂-NH₂ as support and 50% through use of SiO₂-SH as support relative to free cells when cyclohexanone is used as a substrate. The catalysts SiO₂-NH₂-Geotrichum candidum and SiO₂-SH-Geotrichum candidum were recycling and reused in the ɛ-caprolactone synthesis from cyclohexanone, and the biocatalysts promoted a quantitative conversion up to the eighth reaction cycle. KEY POINTS: • Immobilized microorganism is more efficient than free cell in the caprolactone synthesis. • The reaction times for amino and thiol groups in support were 3 h and 2 h, respectively. • These catalysts showed higher ɛ-caprolactone conversion at higher concentrations.

Natural Variation in the ‘Control Loop’ of BVMOAFL210 and Its Influence on Regioselectivity and Sulfoxidation

Baeyer-Villiger monooxygenases (BVMOs) are flavin-dependent enzymes that primarily convert ketones to esters, but can also catalyze heteroatom oxidation. Several structural studies have highlighted the importance of the ‘control loop’ in BVMOs, which adopts different conformations during catalysis. Central to the ‘control loop’ is a conserved tryptophan that has been implicated in NADP(H) binding. BVMOAFL210 from Aspergillus flavus, however, contains a threonine in the equivalent position. Here, we report the structure of BVMOAFL210 in complex with NADP+ in both the ‘open’ and ‘closed’ conformations. In neither conformation does Thr513 contact the NADP+. Although mutagenesis of Thr513 did not significantly alter the substrate scope, changes in peroxyflavin stability and reaction rates were observed. Mutation of this position also brought about changes in the regio- and enantioselectivity of the enzyme. Moreover, lower rates of overoxidation during sulfoxidation of thioanisole were also observed.

The “Green” FMOs: Diversity, Functionality and Application of Plant Flavoproteins

Flavin-dependent monooxygenases (FMOs) are ancient enzymes present in all kingdoms of life. FMOs typically catalyze the incorporation of an oxygen atom from molecular oxygen into small molecules. To date, the majority of functional characterization studies have been performed on mammalian, fungal and bacterial FMOs, showing that they play fundamental roles in drug and xenobiotic metabolism. By contrast, our understanding of FMOs across the plant kingdom is very limited, despite plants possessing far greater FMO diversity compared to both bacteria and other multicellular organisms. Here, we review the progress of plant FMO research, with a focus on FMO diversity and functionality. Significantly, of the FMOs characterized to date, they all perform oxygenation reactions that are crucial steps within hormone metabolism, pathogen resistance, signaling and chemical defense. This demonstrates the fundamental role FMOs have within plant metabolism, and presents significant opportunities for future research pursuits and downstream applications.

Advances in targeting and heterologous expression of genes involved in the synthesis of fungal secondary metabolites

The revolutionary discovery of penicillin only marks the start of our exploration for valuable fungal natural products. Advanced genome sequencing technologies have translated the fungal genome into a huge reservoir of "recipes" - biosynthetic gene clusters (BGCs) - for biosynthesis. Studying complex fungal genetics demands specific gene manipulation strategies. This review summarizes the current progress in efficient gene targeting in fungal cells and heterologous expression systems for expressing fungal BGCs of fungal secondary metabolites.

Regio- and Enantio-selective Chemo-enzymatic C-H-Lactonization of Decanoic Acid to (S)-δ-Decalactone

The conversion of saturated fatty acids to high value chiral hydroxy-acids and lactones poses a number of synthetic challenges: the activation of unreactive C-H bonds and the need for regio- and stereoselectivity. Here the first example of a wild-type cytochrome P450 monooxygenase (CYP116B46 from Tepidiphilus thermophilus) capable of enantio- and regioselective C5 hydroxylation of decanoic acid 1 to (S)-5-hydroxydecanoic acid 2 is reported. Subsequent lactonization yields (S)-δ-decalactone 3, a high value fragrance compound, with greater than 90 % ee. Docking studies provide a rationale for the high regio- and enantioselectivity of the reaction.

Biotechnological Methods of Sulfoxidation: Yesterday, Today, Tomorrow

The production of chiral sulphoxides is an important part of the chemical industry since they have been used not only as pharmaceuticals and pesticides, but also as catalysts or functional materials. The main purpose of this review is to present biotechnological methods for the oxidation of sulfides. The work consists of two parts. In the first part, examples of biosyntransformation of prochiral sulfides using whole cells of bacteria and fungi are discussed. They have more historical significance due to the low predictability of positive results in relation to the workload. In the second part, the main enzymes responsible for sulfoxidation have been characterized such as chloroperoxidase, dioxygenases, cytochrome flavin-dependent monooxygenases, and P450 monooxygenases. Particular emphasis has been placed on the huge variety of cytochrome P450 monooxygenases, and flavin-dependent monooxygenases, which allows for pure sulfoxides enantiomers effectively to be obtained. In the summary, further directions of research on the optimization of enzymatic sulfoxidation are indicated.

Biocatalytic synthesis of lactones and lactams

Cyclic esters and amides (lactones and lactams) are important active ingredients and polymer building blocks. In recent years, numerous biocatalytic methods for their preparation have been developed including enzymatic and chemoenzymatic Baeyer-Villiger oxidations, oxidative lactonisation of diols, and reductive lactonisation and lactamisation of ketoesters. The current state of the art of these methods is reviewed.

Mining the Genome of Streptomyces leeuwenhoekii: Two New Type I Baeyer-Villiger Monooxygenases From Atacama Desert

Actinobacteria are an important source of commercial (bio)compounds for the biotechnological and pharmaceutical industry. They have also been successfully exploited in the search of novel biocatalysts. We set out to explore a recently identified actinomycete, Streptomyces leeuwenhoekii C34, isolated from a hyper-arid region, the Atacama desert, for Baeyer–Villiger monooxygenases (BVMOs). Such oxidative enzymes are known for their broad applicability as biocatalysts by being able to perform various chemical reactions with high chemo-, regio-, and/or enantioselectivity. By choosing this specific Actinobacterium, which comes from an extreme environment, the respective enzymes are also expected to display attractive features by tolerating harsh conditions. In this work, we identified two genes in the genome of S. leeuwenhoekii (sle_13190 and sle_62070) that were predicted to encode for Type I BVMOs, the respective flavoproteins share 49% sequence identity. The two genes were cloned, overexpressed in E. coli with phosphite dehydrogenase (PTDH) as fusion partner and successfully purified. Both flavin-containing proteins showed NADPH-dependent Baeyer–Villiger oxidation activity for various ketones and sulfoxidation activity with some sulfides. Gratifyingly, both enzymes were found to be rather robust by displaying a relatively high apparent melting temperature (45°C) and tolerating water-miscible cosolvents. Specifically, Sle_62070 was found to be highly active with cyclic ketones and displayed a high regioselectivity by producing only one lactone from 2-phenylcyclohexanone, and high enantioselectivity by producing only normal (-)-1S,5R and abnormal (-)-1R,5S lactones (ee > 99%) from bicyclo[3.2.0]hept-2-en-6-one. These two newly discovered BVMOs add two new potent biocatalysts to the known collection of BVMOs.