Immobilization of a Bacterial Cytochrome P450 Monooxygenase System on a Solid Support

Structural and spectroscopic characterization of RufO indicates a new biological role in rufomycin biosynthesis

Rufomycins constitute a class of cyclic heptapeptides isolated from actinomycetes. They are secondary metabolites that show promising treatment against Mycobacterium tuberculosis infections by inhibiting a novel drug target. Several nonproteinogenic amino acids are integrated into rufomycins, including a conserved 3-nitro-tyrosine. RufO, a cytochrome P450 (CYP)-like enzyme, was proposed to catalyze the formation of 3-nitro-tyrosine in the presence of O2 and NO. To define its biological function, the interaction between RufO and the proposed substrate tyrosine is investigated using various spectroscopic methods that are sensitive to the structural change of a heme center. However, a low- to high-spin state transition and a dramatic increase in the redox potential that are commonly found in CYPs upon ligand binding have not been observed. Furthermore, a 1.89-Å crystal structure of RufO shows that the enzyme has flexible surface regions, a wide-open substrate access tunnel, and the heme center is largely exposed to solvent. Comparison with a closely related nitrating CYP reveals a spacious and hydrophobic distal pocket in RufO, which is incapable of stabilizing a free amino acid. Molecular docking validates the experimental data and proposes a possible substrate. Collectively, our results disfavor tyrosine as the substrate of RufO and point to the possibility that the nitration occurs during or after the assembly of the peptides. This study indicates a new function of the unique nitrating enzyme and provides insights into the biosynthesis of nonribosomal peptides.

Nanocarriers-based immobilization of enzymes for industrial application

Nanocarriers-based immobilization strategies are a novel concept in the enhancement of enzyme stability, shelf life and efficiency. A wide range of natural and artificial supports have been assessed for their efficacy in enzyme immobilization. Nanomaterials epitomize unique and fascinating matrices for enzyme immobilization. These structures include carbon nanotubes, superparamagnetic nanoparticles and nanofibers. These nano-based supports offer stable attachment of enzymes, thus ensuring their reusability in diverse industrial applications. This review attempts to encompass recent developments in the critical role played by nanotechnology towards the improvement of the practical applicability of microbial enzymes. Nanoparticles are increasingly being used in combination with various polymers to facilitate enzyme immobilization. These endeavors are proving to be conducive for enzyme-catalyzed industrial operations. In recent years the diversity of nanomaterials has grown tremendously, thus offering endless opportunities in the form of novel combinations for various biotransformation experimentations. These nanocarriers are advantageous for both free enzymes and whole-cell immobilization, thus demonstrating to be relatively effective in several fermentation procedures.

Multicatalytic Hybrid Materials for Biocatalytic and Chemoenzymatic Cascades—Strategies for Multicatalyst (Enzyme) Co-Immobilization

During recent decades, the use of enzymes or chemoenzymatic cascades for organic chemistry has gained much importance in fundamental and industrial research. Moreover, several enzymatic and chemoenzymatic reactions have also served in green and sustainable manufacturing processes especially in fine chemicals, pharmaceutical, and flavor/fragrance industries. Unfortunately, only a few processes have been applied at industrial scale because of the low stabilities of enzymes along with the problematic processes of their recovery and reuse. Immobilization and co-immobilization offer an ideal solution to these problems. This review gives an overview of all the pathways for enzyme immobilization and their use in integrated enzymatic and chemoenzymatic processes in cascade or in a one-pot concomitant execution. We place emphasis on the factors that must be considered to understand the process of immobilization. A better understanding of this fundamental process is an essential tool not only in the choice of the best route of immobilization but also in the understanding of their catalytic activity.

A tailor-made, self-sufficient and recyclable monooxygenase catalyst based on coimmobilized cytochrome P450 BM3 and glucose dehydrogenase

Cytochrome P450 monooxygenases (P450s) promote hydroxylations in a broad variety of substrates. Their prowess in C-H bond functionalization renders P450s promising catalysts for organic synthesis. However, operating P450 reactions involve complex management of the main substrates, O₂ and nicotinamide adenine dinucleotide phosphate (NAD(P)H) reducing equivalents against an overall background of low operational stability. Whole-cell biocatalysis, although often used, offers no general solution to these problems. Herein, we present the design of a tailor-made, self-sufficient, operationally stabilized and recyclable P450 catalyst on porous solid support. Using enzymes as fusion proteins with the polycationic binding module Z_basic2 , the P450s BM3 (from Bacillus megaterium) was coimmobilized with glucose dehydrogenase (type IV; from B. megaterium) on anionic sulfopropyl-activated carrier (ReliSorb SP). Immobilization via Z_basic2 enabled each enzyme to be loaded in controllable amount, thus maximizing the relative portion of the rate limiting P450 BM3 (up to 19.5 U/g_carrier ) in total enzyme immobilized. Using lauric acid as a representative P450 substrate that is poorly accessible to whole-cell catalysts, we demonstrate complete hydroxylation at low catalyst loading (≤0.1 mol%) and efficient electron coupling (74%), inside of the catalyst particle, to the regeneration of NADPH from glucose (27 cycles) was achieved. The immobilized P450 BM3 showed a total turnover number of ∼18,000, thus allowing active catalyst to be recycled up to 20 times. This study therefore supports the idea of practical heterogeneous catalysis by P450s systems immobilized on solid support.

A Stable Artificial Multienzymatic Complex Using a Heterotrimeric Protein From Metallosphaera sedula

Bacterial cytochrome P450 monooxygenases (P450s) are promising biocatalysts for chemical syntheses because they catalyze a variety of oxidations on non-activated hydrocarbons using O₂ . However, the requirement of two auxiliary proteins, an electron transfer protein and a reductase, for the catalysis is a major bottleneck for in vitro applications of these monooxygenases. The authors previous study showed that artificial assembly of a bacterial P450 with its auxiliary proteins using a heterotrimeric proliferating cell nuclear antigen (PCNA) from Sulfolobus solfataricus yields a self-sufficient P450, but partial dissociation of P450 from the complex at catalytic concentrations reduces the apparent specific activity of this self-sufficient P450. In this study, a Metallosphaera sedula PCNA is used, which is currently the most stable heterotrimeric PCNA, to assemble a bacterial P450 with its auxiliary proteins at submicromolar protein concentrations. The apparent specific monooxygenase activity of the M. sedula PCNA-assembled P450 with auxiliary proteins is saturated at protein concentrations of 40 nM, and is 2.1-fold higher than that of the S. solfataricus PCNA-assembled P450. Therefore, M. sedula PCNA represents a versatile tool to facilitate multiple enzymatic reactions, including the P450 monooxygenase system.

Enhanced Performance of Magnetic Graphene Oxide-Immobilized Laccase and Its Application for the Decolorization of Dyes

In this study, magnetic graphene oxide (MGO) nanomaterials were synthesized based on covalent binding of amino Fe₃O₄ nanoparticles onto the graphene oxide (GO), and the prepared MGO was successfully applied as support for the immobilization of laccase. The MGO-laccase was characterized by transmission electron microscopy (TEM) and a vibrating sample magnetometer (VSM). Compared with free laccase, the MGO-laccase exhibited better pH and thermal stabilities. The optimum pH and temperature were confirmed as pH 3.0 and 35 °C. Moreover, the MGO-laccase exhibited sufficient magnetic response and satisfied reusability after being retained by magnetic separation. The MGO-laccase maintained 59.8% activity after ten uses. MGO-laccase were finally utilized in the decolorization of dye solutions and the decolorization rate of crystal violet (CV), malachite green (MG), and brilliant green (BG) reached 94.7% of CV, 95.6% of MG, and 91.4% of BG respectively. The experimental results indicated the MGO-laccase nanomaterials had a good catalysis ability to decolorize dyes in aqueous solution. Compared with the free enzyme, the employment of MGO as enzyme immobilization support could efficiently enhance the availability and facilitate the application of laccase.