The dodecameric vanadium-dependent haloperoxidase from the marine algae Corallina officinalis: cloning, expression, and refolding of the recombinant enzyme

Recombinant protein expression: Challenges in production and folding related matters

Protein folding is a biophysical process by which proteins reach a specific three-dimensional structure. The amino acid sequence of a polypeptide chain contains all the information needed to determine the final three-dimensional structure of a protein. When producing a recombinant protein, several problems can occur, including proteolysis, incorrect folding, formation of inclusion bodies, or protein aggregation, whereby the protein loses its natural structure. To overcome such limitations, several strategies have been developed to address each specific issue. Identification of proper protein refolding conditions can be challenging, and to tackle this high throughput screening for different recombinant protein folding conditions can prove a sound solution. Different approaches have emerged to tackle refolding issues. One particular approach to address folding issues involves molecular chaperones, highly conserved proteins that contribute to proper folding by shielding folding proteins from other proteins that could hinder the process. Proper protein folding is one of the main prerequisites for post-translational modifications. Incorrect folding, if not dealt with, can lead to a buildup of protein misfoldings that damage cells and cause widespread abnormalities. Said post-translational modifications, widespread in eukaryotes, are critical for protein structure, function and biological activity. Incorrect post-translational protein modifications may lead to individual consequences or aggregation of therapeutic proteins. In this review article, we have tried to examine some key aspects of recombinant protein expression. Accordingly, the relevance of these proteins is highlighted, major problems related to the production of recombinant protein and to refolding issues are pinpointed and suggested solutions are presented. An overview of post-translational modification, their biological significance and methods of identification are also provided. Overall, the work is expected to illustrate challenges in recombinant protein expression.

Accurate fragment-based 51-V chemical shift predictions in molecular crystals

Nuclear magnetic resonance (NMR) spectroscopy plays a crucial role in determining molecular structure for complex biological and pharmaceutical compounds. NMR investigations are increasingly reliant on computation for mapping spectral features to chemical structures. Here we benchmark the accuracy of fragment-based ⁵¹V chemical shielding tensor calculations using a training set comprised of 10 biologically and pharmaceutically relevant oxovanadium complexes. Using our self-consistent reproduction of the Madelung potential (SCRMP) electrostatic embedding model, we demonstrate comparable performance between fragment methods and computationally demanding cluster-based techniques. Specifically, fragment methods employing hybrid density functionals are capable of reproducing the experimental ⁵¹V isotropic chemical shifts with a training set rms error of ~9 ​ppm, representing a 20% improvement over traditional plane wave techniques. We provide training set-derived linear regression models for mapping the absolute shieldings obtained from computation to the experimentally determined chemical shifts using four common density functionals; PBE0, B3LYP, PBE, and BLYP. Finally, we establish the utility of fragment methods and the reported regression parameters examining four oxovanadium structures excluded from the training set including the tetracoordinate oxovanadium silicate [Formula: see text] , VO¹⁵NGlySalbz which contains redox-active ligands, and the solid-state form of the common ⁵¹V NMR reference compound VOCl₃.

Scalable High-Performance Production of Recombinant Horseradish Peroxidase from E. coli Inclusion Bodies

Horseradish peroxidase (HRP), an enzyme omnipresent in biotechnology, is still produced from hairy root cultures, although this procedure is time-consuming and only gives low yields. In addition, the plant-derived enzyme preparation consists of a variable mixture of isoenzymes with high batch-to-batch variation preventing its use in therapeutic applications. In this study, we present a novel and scalable recombinant HRP production process in Escherichia coli that yields a highly pure, active and homogeneous single isoenzyme. We successfully developed a multi-step inclusion body process giving a final yield of 960 mg active HRP/L culture medium with a purity of ≥99% determined by size-exclusion high-performance liquid chromatography (SEC-HPLC). The Reinheitszahl, as well as the activity with 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) and 3,3',5,5'-tetramethylbenzidine (TMB) as reducing substrates, are comparable to commercially available plant HRP. Thus, our preparation of recombinant, unglycosylated HRP from E. coli is a viable alternative to the enzyme from plant and highly interesting for therapeutic applications.

Halogenating Enzymes for Active Agent Synthesis: First Steps Are Done and Many Have to Follow

Halogens can be very important for active agents as vital parts of their binding mode, on the one hand, but are on the other hand instrumental in the synthesis of most active agents. However, the primary halogenating compound is molecular chlorine which has two major drawbacks, high energy consumption and hazardous handling. Nature bypassed molecular halogens and evolved at least six halogenating enzymes: Three kind of haloperoxidases, flavin-dependent halogenases as well as α-ketoglutarate and S-adenosylmethionine (SAM)-dependent halogenases. This review shows what is known today on these enzymes in terms of biocatalytic usage. The reader may understand this review as a plea for the usage of halogenating enzymes for fine chemical syntheses, but there are many steps to take until halogenating enzymes are reliable, flexible, and sustainable catalysts for halogenation.

Haloperoxidases as catalysts in organic synthesis

The current state-of-the-art of haloperoxidase catalysis in organic synthesis for halogenation reactions is presented in this review.

A Comparative Review on the Catalytic Mechanism of Nonheme Iron Hydroxylases and Halogenases

Enzymatic halogenation and haloperoxidation are unusual processes in biology; however, a range of halogenases and haloperoxidases exist that are able to transfer an aliphatic or aromatic C–H bond into C–Cl/C–Br. Haloperoxidases utilize hydrogen peroxide, and in a reaction with halides (Cl−/Br−), they react to form hypohalides (OCl−/OBr−) that subsequently react with substrate by halide transfer. There are three types of haloperoxidases, namely the iron-heme, nonheme vanadium, and flavin-dependent haloperoxidases that are reviewed here. In addition, there are the nonheme iron halogenases that show structural and functional similarity to the nonheme iron hydroxylases and form an iron(IV)-oxo active species from a reaction of molecular oxygen with α-ketoglutarate on an iron(II) center. They subsequently transfer a halide (Cl−/Br−) to an aliphatic C–H bond. We review the mechanism and function of nonheme iron halogenases and hydroxylases and show recent computational modelling studies of our group on the hectochlorin biosynthesis enzyme and prolyl-4-hydroxylase as examples of nonheme iron halogenases and hydroxylases. These studies have established the catalytic mechanism of these enzymes and show the importance of substrate and oxidant positioning on the stereo-, chemo- and regioselectivity of the reaction that takes place.

Environmental Control of Vanadium Haloperoxidases and Halocarbon Emissions in Macroalgae

Vanadium-dependent haloperoxidases (V-HPO), able to catalyze the reaction of halide ions (Cl^-, Br^-, I^-) with hydrogen peroxide, have a great influence on the production of halocarbons, which in turn are involved in atmospheric ozone destruction and global warming. The production of these haloperoxidases in macroalgae is influenced by changes in the surrounding environment. The first reported vanadium bromoperoxidase was discovered 40 years ago in the brown alga Ascophyllum nodosum. Since that discovery, more studies have been conducted on the structure and mechanism of the enzyme, mainly focused on three types of V-HPO, the chloro- and bromoperoxidases and, more recently, the iodoperoxidase. Since aspects of environmental regulation of haloperoxidases are less well known, the present paper will focus on reviewing the factors which influence the production of these enzymes in macroalgae, particularly their interactions with reactive oxygen species (ROS).

Marine Vanadium-Dependent Haloperoxidases, Their Isolation, Characterization, and Application

Vanadium-dependent haloperoxidases in seaweeds, cyanobacteria, fungi, and possibly phytoplankton play an important role in the release of halogenated volatile compounds in the environment. These halocarbons have effects on atmospheric chemistry since they cause ozone depletion. In this chapter, a survey is given of the different sources of these enzymes, some of their properties, the various methods to isolate them, and the bottlenecks in purification. The assays to detect and quantify haloperoxidase activity are described as well as their kinetic properties. Several practical tips and pitfalls are given which have not yet been published explicitly. Recent developments in research on structure and function of these enzymes are reviewed. Finally, the application of vanadium-dependent haloperoxidases in the biosynthesis of brominated and other compounds is discussed.

Development of Halogenase Enzymes for Use in Synthesis

Nature has evolved halogenase enzymes to regioselectively halogenate a diverse range of biosynthetic precursors, with the halogens introduced often having a profound effect on the biological activity of the resulting natural products. Synthetic endeavors to create non-natural bioactive small molecules for pharmaceutical and agrochemical applications have also arrived at a similar conclusion: halogens can dramatically improve the properties of organic molecules for selective modulation of biological targets in vivo. Consequently, a high proportion of pharmaceuticals and agrochemicals on the market today possess halogens. Halogenated organic compounds are also common intermediates in synthesis and are particularly valuable in metal-catalyzed cross-coupling reactions. Despite the potential utility of organohalogens, traditional nonenzymatic halogenation chemistry utilizes deleterious reagents and often lacks regiocontrol. Reliable, facile, and cleaner methods for the regioselective halogenation of organic compounds are therefore essential in the development of economical and environmentally friendly industrial processes. A potential avenue toward such methods is the use of halogenase enzymes, responsible for the biosynthesis of halogenated natural products, as biocatalysts. This Review will discuss advances in developing halogenases for biocatalysis, potential untapped sources of such biocatalysts and how further optimization of these enzymes is required to achieve the goal of industrial scale biohalogenation.

[The vanadium compounds: chemistry, synthesis, insulinomimetic properties]

The review considers the biological role of vanadium, its participation in various processes in humans and other mammals, and the anti-diabetic effect of its compounds. Vanadium salts have persistent hypoglycemic and antihyperlipidemic effects and reduce the probability of secondary complications in animals with experimental diabetes. The review contains a detailed description of all major synthesized vanadium complexes having antidiabetic activity. Currently, vanadium complexes with organic ligands are more effective and safer than the inorganic salts. Despite the proven efficacy of these compounds as the anti-diabetic agents in animal models, only one organic complex of vanadium is currently under the second phase of clinical trials. All of the considered data suggest that vanadium compound are a new promising class of drugs in modern pharmacotherapy of diabetes.

cDNA cloning and characterization of vanadium-dependent bromoperoxidases from the red alga Laurencia nipponica

The marine red alga genus Laurencia is one of the richest producers of unique brominated compounds in the marine environment. The cDNAs for two Laurencia nipponica vanadium-dependent bromoperoxidases (LnVBPO1 and LnVBPO2) were cloned and expressed in Escherichia coli. Enzyme assays of recombinant LnVBPO1 and LnVBPO2 using monochlorodimedone revealed that they were thermolabile but their Km values for Br− were significantly lower than other red algal VBPOs. The bromination reaction was also assessed using laurediol, the predicted natural precursor of the brominated ether laurencin. Laurediol, protected by trimethylsilyl at the enyne, was converted to deacetyllaurencin by the LnVBPOs, which was confirmed by tandem mass spectrometry. Native LnVBPO partially purified from algal bodies was active, suggesting that LnVBPO is functional in vivo. These results contributed to our knowledge of the biosynthesis of Laurencia brominated metabolites.

CHARACTERIZATION OF A FUNCTIONAL VANADIUM-DEPENDENT BROMOPEROXIDASE IN THE MARINE CYANOBACTERIUM SYNECHOCOCCUS SP. CC9311(1)

Vanadium-dependent bromoperoxidases (VBPOs) are characterized by the ability to oxidize halides using hydrogen peroxide. These enzymes are well-studied in eukaryotic macroalgae and are known to produce a variety of brominated secondary metabolites. Though genes have been annotated as VBPO in multiple prokaryotic genomes, they remain uncharacterized. The genome of the coastal marine cyanobacterium Synechococcus sp. CC9311 encodes a predicted VBPO (YP_731869.1, sync_2681), and in this study, we show that protein extracts from axenic cultures of Synechococcus possess bromoperoxidase activity, oxidizing bromide and iodide, but not chloride. In-gel activity assays of Synechococcus proteins separated using PAGE reveal a single band having VBPO activity. When sequenced via liquid chromatography/mass spectrometry/mass spectrometry (LC/MS/MS), peptides from the band aligned to the VBPO sequence predicted by the open reading frame (ORF) sync_2681. We show that a VBPO gene is present in a closely related strain, Synechococcus sp. WH8020, but not other clade I Synechococcus strains, consistent with recent horizontal transfer of the gene into Synechococcus. Diverse cyanobacterial-like VBPO genes were detected in a pelagic environment off the California coast using PCR. Investigation of functional VBPOs in unicellular cyanobacteria may lead to discovery of novel halogenated molecules and a better understanding of these organisms' chemical ecology and physiology.

Exploring the chemistry and biology of vanadium-dependent haloperoxidases

Nature has developed an exquisite array of methods to introduce halogen atoms into organic compounds. Most of these enzymes are oxidative and require either hydrogen peroxide or molecular oxygen as a cosubstrate to generate a reactive halogen atom for catalysis. Vanadium-dependent haloperoxidases contain a vanadate prosthetic group and utilize hydrogen peroxide to oxidize a halide ion into a reactive electrophilic intermediate. These metalloenzymes have a large distribution in nature, where they are present in macroalgae, fungi, and bacteria, but have been exclusively characterized in eukaryotes. In this minireview, we highlight the chemistry and biology of vanadium-dependent haloperoxidases from fungi and marine algae and the emergence of new bacterial members that extend the biological function of these poorly understood halogenating enzymes.

Critical view on the monochlorodimedone assay utilized to detect haloperoxidase activity

The current study aimed to identify the halogenating enzymes involved in the biosynthesis of the ambigols A, B, C and tjipanazole D, isolated from the cyanobacterium Fischerella ambigua. Haloperoxidase (HPO) activity within F. ambigua was therefore assayed spectrophotometrically by using monochlorodimedone (MCD) during protein purification. This strategy revealed the isolation of a protein positive in the MCD-assay, but an involvement in halogenating processes could not be verified. N-terminal sequencing rather demonstrated homology to cytochrome c(6) from other cyanobacteria and green algae. From our findings it thus has to be concluded that the spectrophotometrical MCD-assay routinely used to detect HPO activity may yield false positive results, mainly since the assay focuses on the decline of the educt and not on the formation of the product. Our data indicate that the reaction of MCD with proteins of the cytochrome c- family leads to unspecific products.