Cholesterol oxidase: biotechnological applications

A Facile LC-MS Method for Profiling Cholesterol and Cholesteryl Esters in Mammalian Cells and Tissues

Cholesterol is central to mammalian lipid metabolism and serves many critical functions in the regulation of diverse physiological processes. Dysregulation in cholesterol metabolism is causally linked to numerous human diseases, and therefore, in vivo, the concentrations and flux of cholesterol and cholesteryl esters (fatty acid esters of cholesterol) are tightly regulated. While mass spectrometry has been an analytical method of choice for detecting cholesterol and cholesteryl esters in biological samples, the hydrophobicity, chemically inert nature, and poor ionization of these neutral lipids have often proved a challenge in developing lipidomics compatible liquid chromatography-mass spectrometry (LC-MS) methods to study them. To overcome this problem, here, we report a reverse-phase LC-MS method that is compatible with existing high-throughput lipidomics strategies and capable of identifying and quantifying cholesterol and cholesteryl esters from mammalian cells and tissues. Using this sensitive yet robust LC-MS method, we profiled different mammalian cell lines and tissues and provide a comprehensive picture of cholesterol and cholesteryl esters content in them. Specifically, among cholesteryl esters, we find that mammalian cells and tissues largely possess monounsaturated and polyunsaturated variants. Taken together, our lipidomics compatible LC-MS method to study this lipid class opens new avenues in understanding systemic and tissue-level cholesterol metabolism under various physiological conditions.

Leveraging insect viruses and genetic manipulation for sustainable agricultural pest control

The potential of insect viruses in the biological control of agricultural pests is well-recognized, yet their practical application faces obstacles such as host specificity, variable virulence, and resource scarcity. High-throughput sequencing (HTS) technologies have significantly advanced our capabilities in discovering and identifying new insect viruses, thereby enriching the arsenal for pest management. Concurrently, progress in reverse genetics has facilitated the development of versatile viral expression vectors. These vectors have enhanced the specificity and effectiveness of insect viruses in targeting specific pests, offering a more precise approach to pest control. This review provides a comprehensive examination of the methodologies employed in the identification of insect viruses using HTS. Additionally, it explores the domain of genetically modified insect viruses and their associated challenges in pest management. The adoption of these cutting-edge approaches holds great promise for developing environmentally sustainable and effective pest control solutions. © 2023 Society of Chemical Industry.

The importance of choosing the appropriate cholesterol quantification method: enzymatic assay versus gas chromatography

Cholesterol is a major lipid of the animal realm with many biological roles. It is an important component of cellular membranes and a precursor of steroid hormones and bile acids. It is particularly abundant in nervous tissues, and dysregulation of cholesterol metabolism has been associated with neurodegenerative diseases such as Alzheimer's and Huntington's diseases. Deciphering the pathophysiological mechanisms of these disorders often involves animal models such as mice and Drosophila. Accurate quantification of cholesterol levels in the chosen models is a critical point of these studies. In the present work, we compare two common methods, gas chromatography coupled to flame-ionization detection (GC/FID) and a cholesterol oxidase-based fluorometric assay to measure cholesterol in mouse brains and Drosophila heads. Cholesterol levels measured by the two methods were similar for the mouse brain, which presents a huge majority of cholesterol in its sterol profile. On the contrary, depending on the method, measured cholesterol levels were very different for Drosophila heads, which present a complex sterol profile with a minority of cholesterol. We showed that the enzyme-based assay is not specific for cholesterol and detects other sterols as well. This method is therefore not suited for cholesterol measurement in models such as Drosophila. Alternatively, chromatographic methods, such as GC/FID, offer the required specificity for cholesterol quantification. Understanding the limitations of the quantification techniques is essential for reliable interpretation of the results in cholesterol-related research.

New insights into the substrate specificity of cholesterol oxidases for more aware application

Cholesterol oxidases (ChOxes) are enzymes that catalyze the oxidation of cholesterol to cholest-4-en-3-one. These enzymes find wide applications across various diagnostic and industrial settings. In addition, as a pathogenic factor of several bacteria, they have significant clinical implications. The current classification system for ChOxes is based on the type of bond connecting FAD to the apoenzyme, which does not adequately illustrate the enzymatic and structural characteristics of these proteins. In this study, we have adopted an integrative approach, combining evolutionary analysis, classic enzymatic techniques and computational approaches, to elucidate the distinct features of four various ChOxes from Rhodococcus sp. (RCO), Cromobacterium sp. (CCO), Pseudomonas aeruginosa (PCO) and Burkhoderia cepacia (BCO). Comparative and evolutionary analysis of substrate-binding domain (SBD) and FAD-binding domain (FBD) helped to reveal the origin of ChOxes. We discovered that all forms of ChOxes had a common ancestor and that the structural differences evolved later during divergence. Further examination of amino acid variations revealed SBD as a more variable compared to FBD independently of FAD coupling mechanism. Revealed differences in amino acid positions turned out to be critical in determining common for ChOxes properties and those that account for the individual differences in substrate specificity. A novel look with the help of chemical descriptors on found distinct features were sufficient to attempt an alternative classification system aimed at application approach. While univocal characteristics necessary to establish such a system remain elusive, we were able to demonstrate the substrate and protein features that explain the differences in substrate profile.

Improved production of Bacillus subtilis cholesterol oxidase by optimization of process parameters using response surface methodology

BACKGROUND

Cholesterol oxidase has numerous biomedical and industrial applications. In the current study, a new bacterial strain was isolated from sewage and was selected for its high potency for cholesterol degradation (%) and production of high cholesterol oxidase activity (U/OD600).

RESULTS

Based on the sequence of 16S rRNA gene, the bacterium was identified as Bacillus subtilis. The fermentation conditions affecting cholesterol degradation (%) and the activity of cholesterol oxidase (U/OD600) of B. subtilis were optimized through fractional factorial design (FFD) and response surface methodology (RSM). According to this sequential optimization approach, 80.152% cholesterol degradation was achieved by setting the concentrations of cholesterol, inoculum size, and magnesium sulphate at 0.05 g/l, 6%, and 0.05 g/l, respectively. Moreover, 85.461 U of cholesterol oxidase/OD600 were attained by adjusting the fermentation conditions at initial pH, 6; volume of the fermentation medium, 15 ml/flask; and concentration of cholesterol, 0.05 g/l. The optimization process improved cholesterol degradation (%) and the activity of cholesterol oxidase (U/OD600) by 139% and 154%, respectively. No cholesterol was detected in the spectroscopic analysis of the optimized fermented medium via gas chromatography-mass spectroscopy (GC-MS).

CONCLUSION

The current study provides principal information for the development of efficient production of cholesterol oxidase by B. subtilis that could be used in various applications.

Directed evolution of cholesterol oxidase with improved thermostability using error-prone PCR

Cholesterol oxidase is industrially important as it is frequently used as a biosensor in food and agriculture industries and measurement of cholesterol. Although, most natural enzymes show low thermostability, which limits their application. Here, we obtained an improved variant of Chromobacterium sp. DS1 cholesterol oxidase (ChOS) with enhanced thermostability by random mutant library applying two forms of error-prone PCR (serial dilution and single step). Wild-type ChOS indicated an optimal temperature and pH of 70 ºC and pH 7.5, respectively. The best mutant ChOS-M acquired three amino acid substitutions (S112T, I240V and A500S) and enhanced thermostability (at 50 °C for 5 h) by 30%. The optimum temperature and pH in the mutant were not changed. In comparison to wild type, circular dichroism disclosed no significant secondary structural alterations in mutants. These findings show that error-prone PCR is an effective method for enhancing enzyme characteristics and offers a platform for the practical use of ChOS as a thermal-resistance enzyme in industrial fields and clinical diagnosis.

Biomimetic Antithrombotic Tissue-Engineered Vascular Grafts for Converting Cholesterol and Free Radicals into Nitric Oxide

Small-diameter tissue-engineered vascular grafts (sdTEVGs) are essential materials used in bypass or replacement surgery for cardiovascular diseases; however, their application efficacy is limited because of patency rates, especially under hyperlipidemia, which is also clinically observed in patients with cardiovascular diseases. In such cases, improving sdTEVG patency is challenging because cholesterol crystals easily cause thrombosis and impede endothelialization. Herein, the development of a biomimetic antithrombotic sdTEVG incorporating cholesterol oxidase and arginine into biomineralized collagen-gold hydrogels on a sdTEVG surface is described. Biomimetic antithrombotic sdTEVGs represent a multifunctional substrate for the green utilization of hazardous substances and can convert cholesterol into hydrogen peroxide, which can react with arginine to generate nitric oxide (NO). NO is a vasodilator that can simulate the antithrombotic action of endothelial cells under hyperlipidemic conditions. In vivo studies show that sdTEVGs can rapidly produce large amounts of NO via a cholesterol catalytic cascade to inhibit platelet aggregation, thereby improving the blood flow velocity and patency rates 60 days after sdTEVG transplantation. A practical and reliable strategy for transforming "harmful" substances into "beneficial" factors at early transplantation stages is presented, which can also promote vascular transplantation in patients with hyperlipidemia.

Production and statistical optimization of cholesterol-oxidase generated by Streptomyces sp. AN strain

Background

Cholesterol oxidases (CHOs) have attracted enormous attention because of their wide biotechnological potential. The present study explores the production of CHOs by Streptomyces sp. AN. Evaluation of culture conditions affecting enzyme production, medium optimization and released metabolite characteristics were also investigated.

Results

The current work reports the isolation of 37 colonies (bacteria/actinobacteria) with different morphotypes from different soil/water samples. The isolate-coded AN was selected for its high potency for CHO production. Morphological characteristics and the obtained partial sequence of 16srRNA of AN showed 99.38% identity to Streptomyces sp. strain P12–37. Factors affecting CHO production were evaluated using Plackett-Burman (PB) and Box-Behnken (BB) statistical designs to find out the optimum level of the most effective variables, namely, pH, starch, NH4NO3 and FeSO4.7H2O with a predicted activity of 6.56 U/mL. According to this optimization, the following medium composition was considered to be optimum (g/L): cholesterol 1, starch 6, MgSO4.7H2O 0.1, CaCl2 0.01, FeSO4.7H2O 0.1, NH4NO3 23.97, yeast extract (YE) 0.2, K2HPO4 0.01, KH2PO4 0.1, NaCl 0.01, Tween 20 0.01, pH 6.36 and incubation temperature (30 °C) for 9 days. Spectophotometric analysis for released metabolites against cholesterol (standard) via Fourier-transform infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) was carried out. FTIR spectrum showed the appearance of new absorption peaks at 1644 and 1725cm−1; this confirmed the presence of the Keto group (C=O) stretch bond. Besides, fermentation caused changes in thermal properties such as melting temperature peak (99.26; 148.77 °C), heat flow (− 8; − 3.6 Mw/mg), capacity (− 924.69; − 209.77 mJ) and heat enthalpy (− 385.29; 69.83 J/g) by comparison to the standard cholesterol as recognized through DSC thermogram. These changes are attributed to the action of the CHO enzyme and the release of keto derivatives of cholesterol with different properties.

Conclusion

Streptomyces sp. AN was endowed with the capability to produce CHO. Enzyme maximization was followed using a statistical experimental approach, leading to a 2.6-fold increase in the overall activity compared to the basal condition. CHO catalyzed the oxidation of cholesterol; this was verified by the appearance of a new keto group (C=O) peak at 1644 and 1725 cm−1 observed by FTIR spectroscopic analysis. Also, DSC thermogram demonstrates the alteration of cholesterol triggered by CHO.

Nanozyme-natural enzymes cascade catalyze cholesterol consumption and reverse cancer multidrug resistance

Multidrug resistance is still a major obstacle to cancer treatment. The most studies are to inhibit the activity of the drug transporter P-glycoprotein (P-gp), but the effect is not ideal. Herein, a nanosystem was built based on cascade catalytic consumption of cholesterol. Cholesterol oxidase (natural enzyme, COD) was immobilized on the carrier (NH₂-MIL-88B, MOF) through amide reaction, COD catalyzed the consumption of cholesterol, the reaction product H₂O₂ was further produced by the MOF with its peroxidase-like activity to produce hydroxyl radicals (•OH) with killing effect. Due to the high expression of CD44 receptor on the surface of tumor cells, we encapsulated chondroitin sulfate gel shell (CS-shell) with CD44 targeting and apoptosis promoting effect on the surface of DOX@MOF-COD nanoparticles, which can accurately and efficiently deliver the drugs to the tumor site and improve the effect of reversing drug resistance. Taking drug-resistant cell membrane as "breakthrough", this paper will provide a new idea for reversing multidrug resistance of tumor.

Enzyme-assisted ReMALDI-MS assay for quantification of cholesterol in food

Cholesterol is a vital building block for animal cell membranes and participates in the synthesis of various hormones. Accurate quantitation of cholesterol in food is crucial for healthy diets. Here, we describe an enzyme-assisted reactive matrix-assisted laser desorption/ionization mass spectrometry (ReMALDI-MS) assay for the quantification of cholesterol in food. First, cholesterol was converted to 4-cholesten-3-one using the cholesterol oxidase, and then reacted with a reactive matrix, 4-hydrazinoquinazoline (4-HQ), to form a hydrazone bond. Utilizing 4-HQ significantly improved the ionization efficiency of cholesterol, which possesses poor ionization efficiency in MALDI-MS, and no additional tedious derivatization/purification steps were needed. Thus, the proposed assay was successfully used for the quantification of cholesterol in bovine milk and cream. The standard recovery tests show a recovery range of 95.3-103.0% with a relative standard deviation of 0.3-3.1%. Therefore, the proposed enzyme-assisted ReMALDI-MS assay has great potential for quantification of cholesterol in other foods.

An engineered cholesterol oxidase catalyses enantioselective oxidation of non-steroidal secondary alcohols

The enantioselective oxidation of 2° alcohols to ketones is an important reaction in synthetic chemistry, especially if it can be achieved using O₂‐driven alcohol oxidases under mild reaction conditions. However to date, oxidation of secondary alcohols using alcohol oxidases has focused on activated benzylic or allylic substrates, with unactivated secondary alcohols showing poor activity. Here we show that cholesterol oxidase (EC 1.1.3.6) could be engineered for activity towards a range of aliphatic, cyclic, acyclic, allylic and benzylic secondary alcohols. Additionally, since the variants demonstrated high (S)‐selectivity, deracemisation reactions were performed in the presence of ammonia borane to obtain enantiopure (R)‐alcohols.

Polyethylene glycol acute and sub-lethal toxicity in neotropical Physalaemus cuvieri tadpoles (Anura, Leptodactylidae)

Although many polymers are known by their toxicity, we know nothing about the impact of polyethylene glycol (PEG) on anurofauna. Its presence in different products and disposal in aquatic environments turn assessments about its impact on amphibians an urgent matter. Accordingly, we tested the hypothesis that short-time exposure (72 h) of tadpoles belonging to the species Physalaemus cuvieri (Anura, Leptodactylidae) to PEG induces oxidative stress and neurotoxicity on them. We observed that polymer uptake in P. cuvieri occurred after exposure to 5 and 10 mg/L of PEG without inducing changes in their nitrite levels neither at the levels of substances reactive to thiobarbituric acid. However, hydrogen peroxide and reactive oxygen species production was higher in animals exposed to PEG, whose catalase and superoxide dismutase levels were not enough to counterbalance the production of these reactive species. Therefore, this finding suggests physiological changes altering REDOX homeostasis into oxidative stress. In addition, the increased activity of acetylcholinesterase and butyrylcholinesterase, and reduction in superficial neuromasts, confirmed PEG's neurotoxic potential. To the best of our knowledge, this is the first report on PEG's biological impact on a particular amphibian species. The study has broadened the understanding about ecotoxicological risks associated with water pollution by these polymers, as well as motivated further investigations on its impacts on amphibians' health and on the dynamics of their natural populations.

Cloning, expression, and in silico structural modeling of cholesterol oxidase of Acinetobacter sp. strain RAMD in E. coli

Cholesterol oxidases (CHOXs) are flavin‐adenine dinucleotide‐dependent oxidoreductases with a range of biotechnological applications. There remains an urgent need to identify novel CHOX family members to meet the demands of enzyme markets worldwide. Here, we report the cloning, heterologous expression, and structural modeling of the cholesterol oxidase of Acinetobacter sp. strain RAMD. The cholesterol oxidase gene was cloned and expressed in pGEM®‐T and pET‐28a(+) vectors, respectively, using a gene‐specific primer based on the putative cholesterol oxidase ORF of Acinetobacter baumannii strain AB030 (GenBank [gb] locus tag: IX87_05230). The obtained nucleotide sequence (1671 bp, gb: MK575469.2), translated to a protein designated choxAB (556 amino acids), was overexpressed as inclusion bodies (IBs) (MW ˜ 62 kDa) in 1 mm IPTG‐induced Escherichia coli BL21 (DE3) Rosetta cells. The optimized expression conditions (1 mm IPTG with 2% [v/v] glycerol and at room temperature) yielded soluble active choxAB of 0.45 U·mL⁻¹, with 56.25‐fold enhancement. The recombinant choxAB was purified to homogeneity using Ni²⁺‐affinity agarose column with specific activity (0.054 U·mg⁻¹), yield (8.1%), and fold purification (11.69). Capillary isoelectric‐focusing indicated pI of 8.77 for choxAB. LC‐MS/MS confirmed the IBs (62 kDa), with 82.6% of the covered sequence being exclusive to A. baumannii cholesterol oxidase (UniProtKB: A0A0E1FG24). The 3D structure of choxAB was predicted using the LOMETS webtool with the cholesterol oxidase template of Streptomyces sp. SA‐COO (PDB: 2GEW). The predicted secondary structure included 18 α‐helices and 12 β‐strands, a predicted catalytic triad (E²²⁰, H³⁸⁰, and N⁵¹⁴), and a conserved FAD‐binding sequence (GSGFGGSVSACRLTEKG). Future studies should consider fusion to solubilization tags and switching to the expression host Pichia pastoris to reduce IB formation.

Raising the 'Good' Oxidants for Immune Protection

Redox medicine is a new therapeutic concept targeting reactive oxygen species (ROS) and secondary reaction products for health benefit. The concomitant function of ROS as intracellular second messengers and extracellular mediators governing physiological redox signaling, and as damaging radicals instigating or perpetuating various pathophysiological conditions will require selective strategies for therapeutic intervention. In addition, the reactivity and quantity of the oxidant species generated, its source and cellular location in a defined disease context need to be considered to achieve the desired outcome. In inflammatory diseases associated with oxidative damage and tissue injury, ROS source specific inhibitors may provide more benefit than generalized removal of ROS. Contemporary approaches in immunity will also include the preservation or even elevation of certain oxygen metabolites to restore or improve ROS driven physiological functions including more effective redox signaling and cell-microenvironment communication, and to induce mucosal barrier integrity, eubiosis and repair processes. Increasing oxidants by host-directed immunomodulation or by exogenous supplementation seems especially promising for improving host defense. Here, we summarize examples of beneficial ROS in immune homeostasis, infection, and acute inflammatory disease, and address emerging therapeutic strategies for ROS augmentation to induce and strengthen protective host immunity.

Can carbon nanofibers affect anurofauna? Study involving neotropical Physalaemus cuvieri (Fitzinger, 1826) tadpoles

Although carbon nanotubes' (CNTs) toxicity in different experimental systems (in vivo and in vitro) is known, little is known about the toxic effects of carbon nanofibers (CNFs) on aquatic vertebrates. We herein investigated the potential impact of CNFs (1 and 10 mg/L) by using Physalaemus cuvieri tadpoles as experimental model. CNFs were able to induce nutritional deficit in animals after 48-h exposure to them, and this finding was inferred by reductions observed in body concentrations of total soluble carbohydrates, total proteins, and triglycerides. The increased production of hydrogen peroxide, reactive oxygen species and thiobarbituric acid reactive substances in tadpoles exposed to CNFs has suggested REDOX homeostasis change into oxidative stress. This process was correlated to the largest number of apoptotic and necrotic cells in the blood of these animals. On the other hand, the increased superoxide dismutase and catalase activity has suggested that the antioxidant system of animals exposed to CNFs was not enough to maintain REDOX balance. In addition, CNFs induced increase in acetylcholinesterase and butyrylcholinesterase activity, as well as changes in the number of neuromasts evaluated on body surface (which is indicative of the neurotoxic effect of nanomaterials on the assessed model system). To the best of our knowledge, this is the first report on the impact of CNFs on amphibians; therefore, it broadened our understanding about ecotoxicological risks associated with their dispersion in freshwater ecosystems and possible contribution to the decline in the populations of anurofauna species.

Comparison of seven different reagents of peroxidase method for small and dense low density lipoprotein cholesterol (sdLDL-C) measurement

Background

We validated the performance of seven different reagents of peroxidase method for sdLDL‐C in two automatic analyzers that are common in Chinese laboratories.

Methods

Seven commercially available sdLDL‐C assays were analyzed with the Beckman AU5400 and Mindray BS2000 automatic analyzers. A total of 336 blood samples were collected and the reference interval was also validated in 298 apparently healthy individuals. Serum samples were used for method comparison of precision, recovery, lower limit of detection, comparison and concurrence analysis, as well as reference interval for the Mindray reagent.

Results

The repeatability CV% of the seven sdLDL‐C assays were 0.81%~3.66% for Mindray BS2000 and 0.76%~3.91% for Beckman AU5400, while Total CVs for Mindray BS2000 sdLDL‐C assay were 1.34%~4.81%, and that of Beckman AU5400 were 2.25%~10.33%. The measured recovery rates of sdLDL‐C assays were within the allowable ±10% deviation range. There was no obvious difference between the reagents in the lower limit detection. There was a difference between the validation results of the reference range and the manufacturer's.BSBE, Mindray, and Dongou had a high degree of association with DENKA SEIKEN on Mindray BS2000, while BSBE, Mindray, Dongou and Merit Choice had a high degree of association with DENKA SEIKEN on Beckman AU5400. Passing–Bablok regression showed excellent linear correlation between BSBE and Mindray and DENKA SEIKEN and on Beckman AU5400.

Conclusions

Our results indicate that the basic performance can meet the testing requirements, but the comparability between them is still insufficient.

Determination of in vitro and in vivo immune response to recombinant cholesterol oxidase from Mycobacterium tuberculosis

Cholesterol oxidase (ChoD) is an enzyme that is involved but is dispensable in the process of cholesterol degradation by Mycobacterium tuberculosis (Mtb). Interestingly, ChoD is a virulence factor of Mtb, and it strongly modulates the function of human macrophages in vitro, allowing the intracellular survival of bacteria. Here, we determined the immunogenic activity of recombinant ChoD from Mtb in a mouse model. We found that peritoneal exudate cells obtained from mice injected i.p. with ChoD but not those from mice injected with PBS responded in vitro with highly spontaneous, as well as phorbol 12-myristate 13-acetate (PMA)-stimulated, production of reactive oxygen species (ROS). However, ChoD significantly reduced the ROS response to PMA in re-stimulated cells in vitro. The cytokine secretion pattern in mice immunized s.c. with ChoD emulsified with incomplete Freund's adjuvant (IFA) showed evidence of Th2-induced or proinflammatory immune responses. The main cytokines detected in sera were interleukin (IL) 6 and 5, tumour necrosis factor α (TNF-α) and monocyte chemoattractant protein 1, while IL-2 and IL-12 as well as interferon γ were undetectable. Similarly, ChoD protein alone activated THP-1-derived macrophages to release proinflammatory IL-6, IL-8 and TNF-α, in vitro. Moreover, a statistically significant predominance of the IgG1 isotype over that of IgG2a in the sera of mice immunized with ChoD/IFA was observed. In conclusion, we demonstrated here that ChoD of Mtb is an active protein, which is able to induce the immune response both in vivo and in vitro.

The multipurpose family of flavoprotein oxidases

This chapter represents a journey through flavoprotein oxidases. The purpose is to excite the reader curiosity regarding this class of enzymes by showing their diverse applications. We start with a brief overview on oxidases to then introduce flavoprotein oxidases and elaborate on the flavin cofactors, their redox and spectroscopic characteristics, and their role in the catalytic mechanism. The six major flavoprotein oxidase families will be described, giving examples of their importance in biology and their biotechnological uses. Specific attention will be given to a few selected flavoprotein oxidases that are not extensively discussed in other chapters of this book. Glucose oxidase, cholesterol oxidase, 5-(hydroxymethyl)furfural (HMF) oxidase and methanol oxidase are four examples of oxidases belonging to the GMC-like flavoprotein oxidase family and that have been shown to be valuable biocatalysts. Their structural and mechanistic features and recent enzyme engineering will be discussed in details. Finally we give a look at the current trend in research and conclude with a future outlook.

Identification of cholesterol-assimilating actinomycetes strain and application of statistical modeling approaches for improvement of cholesterol oxidase production by Streptomyces anulatus strain NEAE-94

Background

Cholesterol oxidase biosensors have been used to determine the level of cholesterol in different serum and food samples. Due to a wide range of industrial and clinical applications of microbial cholesterol oxidase, isolation and identification of a new microbial source (s) of cholesterol oxidase are very important.

Results

The local isolate Streptomyces sp. strain NEAE-94 is a promising source of cholesterol oxidase. It was identified based on cultural, morphological and physiological characteristics; in addition to the 16S rRNA sequence. The sequencing product had been deposited in the GenBank database under the accession number KC354803. Cholesterol oxidase production by Streptomyces anulatus strain NEAE-94 in shake flasks was optimized using surface response methodology. The different process parameters were first screened using a Plackett-Burman design and the parameters with significant effects on the production of cholesterol oxidase were identified. Out of the 15 factors screened, agitation speed, cholesterol and yeast extract concentrations had the most significant positive effects on the production of cholesterol oxidase. The optimal levels of these variables and the effects of their mutual interactions on cholesterol oxidase production were determined using Box-Behnken design. Cholesterol oxidase production by Streptomyces anulatus strain NEAE-94 was 11.03, 27.31 U/mL after Plackett-Burman Design and Box-Behnken design; respectively, with a fold of increase of 6.06 times compared to the production before applying the Plackett-Burman design (4.51 U/mL).

Conclusions

Maximum cholesterol oxidase activity was obtained at the following fermentation conditions: g/L (cholesterol 4, yeast extract 5, NaCl 0.5, K₂HPO₄ 1, FeSO₄.7H₂O 0.01, MgSO₄.7H₂O 0.5), pH 7, inoculum size 4% (v/v), temperature 37°C, agitation speed of 150 rpm, medium volume 50 mL and incubation time 5 days.

Characterization and overproduction of cell-associated cholesterol oxidase ChoD from Streptomyces lavendulae YAKB-15

Cholesterol oxidases are important enzymes with a wide range of applications from basic research to industry. In this study, we have discovered and described the first cell-associated cholesterol oxidase, ChoD, from Streptomyces lavendulae YAKB-15. This strain is a naturally high producer of ChoD, but only produces ChoD in a complex medium containing whole yeast cells. For characterization of ChoD, we acquired a draft genome sequence of S. lavendulae YAKB-15 and identified a gene product containing a flavin adenine dinucleotide binding motif, which could be responsible for the ChoD activity. The enzymatic activity was confirmed in vitro with histidine tagged ChoD produced in Escherichia coli TOP10, which lead to the determination of basic kinetic parameters with K_m 15.9 µM and k_cat 10.4/s. The optimum temperature and pH was 65 °C and 5, respectively. In order to increase the efficiency of production, we then expressed the cholesterol oxidase, choD, gene heterologously in Streptomyces lividans TK24 and Streptomyces albus J1074 using two different expression systems. In S. albus J1074, the ChoD activity was comparable to the wild type S. lavendulae YAKB-15, but importantly allowed production of ChoD without the presence of yeast cells.

Cholesterol Degradation and Production of Extracellular Cholesterol Oxidase from Bacillus pumilus W1 and Serratia marcescens W8

Cholesterol is a waxy substance present in all types of the body cells. The presence of higher concentration of low density lipoprotein (LDL) is characterized by abnormal cholesterol level and is associated with cardiovascular diseases which lead to the development of atheroma in arteries known as atherosclerosis. The transformation of cholesterol by bacterial cholesterol oxidase can provide a key solution for the treatment of diseases related to cholesterol and its oxidized derivatives. Previously isolated bacteria from oil-contaminated soil were screened for cholesterol degradation. Among fourteen, five isolates were able to utilize cholesterol. Two strains Serratia marcescens W1 and Bacillus pumilus W8 using cholesterol as only carbon and energy source were selected for degradation studies. Several parameters (incubation time, substrate concentration, pH, temperature, and different metal ions) for cholesterol decomposition by the selected bacterial strains were evaluated. Maximum cholesterol reduction was achieved on the 5th day of incubation, 1g/L of substrate concentration, pH 7, in the presence of Mg2+ and Ca2+ ions, and at 35°C. Cholesterol degradation was analyzed by enzymatic colorimetric method, thin layer chromatography (TLC), and high-performance liquid chromatography (HPLC). Under optimized conditions 50% and 84% cholesterol reduction were recorded with Serratia marcescens W1 and Bacillus pumilus W8, respectively. Cholesterol oxidase activity was assayed qualitatively and quantitatively. The results revealed that Serratia marcescens W1 and Bacillus pumilus W8 have great potential for cholesterol degradation and would be regarded as a source for cholesterol oxidase (CHO).

Expression optimization, purification, and functional characterization of cholesterol oxidase from Chromobacterium sp. DS1

Cholesterol oxidase is a bifunctional bacterial flavoenzyme which catalyzes oxidation and isomerization of cholesterol. This valuable enzyme has attracted a great deal of attention because of its wide application in the clinical laboratory, synthesis of steroid derived drugs, food industries, and its potentially insecticidal activity. Therefore, development of an efficient protocol for overproduction of cholesterol oxidase could be valuable and beneficial in this regard. The present study examined the role of various parameters (host strain, culture media, induction time, isopropyl ß-D-1-thiogalactopyranoside concentration, as well as post-induction incubation time and temperature) on over-expression of cholesterol oxidase from Chromobacterium sp. DS1. Applying the optimized protocol, the yield of recombinant cholesterol oxidase significantly increased from 92 U/L to 2115 U/L. Under the optimized conditions, the enzyme was produced on a large-scale, and overexpressed cholesterol oxidase was purified from cell lysate by column nickel affinity chromatography. K_m and V_max values of the purified enzyme for cholesterol were estimated using Lineweaver-Burk plot. Further, the optimum pH and optimum temperature for the enzyme activity were determined. This study reports a straightforward protocol for cholesterol oxidase production which can be performed in any laboratory.

Expression optimization of recombinant cholesterol oxidase in Escherichia coli and its purification and characterization

Cholesterol oxidase is a bacterial flavoenzyme which catalyzes oxidation and isomerization of cholesterol. This enzyme has a great commercial value because of its wide applications in cholesterol analysis of clinical samples, synthesis of steroid-derived drugs, food industries, and potentially insecticidal activity. Accordingly, development of an efficient protocol for overexpression of cholesterol oxidase can be very valuable and beneficial. In this study, expression optimization of cholesterol oxidase from Streptomyces sp. SA-COO was investigated in Escherichia coli host strains. Various parameters that may influence the yield of a recombinant enzyme were evaluated individually. The optimal host strain, culture media, induction time, Isopropyl ß-d-1-thiogalactopyranoside concentration, as well as post-induction incubation time and temperature were determined in a shaking flask mode. Applying the optimized protocol, the production of recombinant cholesterol oxidase was significantly enhanced from 3.2 to 158 U/L. Under the optimized condition, the enzyme was produced on a large-scale, and highly expressed cholesterol oxidase was purified from cell lysate by column nickel affinity chromatography. K_m and V_max values of the purified enzyme for cholesterol were estimated using Lineweaver–Burk plot. Further, the optimum pH and optimum temperature for the enzyme activity were also determined. We report a straightforward and easy protocol for cholesterol oxidase production which can be performed in any laboratory.

Structure-Based Engineering of Phanerochaete chrysosporium Alcohol Oxidase for Enhanced Oxidative Power toward Glycerol

Glycerol is a major byproduct of biodiesel production, and enzymes that oxidize this compound have been long sought after. The recently described alcohol oxidase from the white-rot basidiomycete Phanerochaete chrysosporium (PcAOX) was reported to feature very mild activity on glycerol. Here, we describe the comprehensive structural and biochemical characterization of this enzyme. PcAOX was expressed in Escherichia coli in high yields and displayed high thermostability. Steady-state kinetics revealed that PcAOX is highly active toward methanol, ethanol, and 1-propanol (k_cat = 18, 19, and 11 s^–1, respectively), but showed very limited activity toward glycerol (k_obs = 0.2 s^–1 at 2 M substrate). The crystal structure of the homo-octameric PcAOX was determined at a resolution of 2.6 Å. The catalytic center is a remarkable solvent-inaccessible cavity located at the re side of the flavin cofactor. Its small size explains the observed preference for methanol and ethanol as best substrates. These findings led us to design several cavity-enlarging mutants with significantly improved activity toward glycerol. Among them, the F101S variant had a high k_cat value of 3 s^–1, retaining a high degree of thermostability. The crystal structure of F101S PcAOX was solved, confirming the site of mutation and the larger substrate-binding pocket. Our data demonstrate that PcAOX is a very promising enzyme for glycerol biotransformation.

Use of an Isotope-Coded Mass Tag (ICMT) Method To Determine the Orientation of Cholesterol Oxidase on Model Membranes

Although the interfacial membrane protein cholesterol oxidase is structurally and kinetically well-characterized, its orientation in and mode of interaction with cholesterol-containing membranes have not been established. Cholesterol oxidase can alter the structure of the cell membrane in pathogenic bacteria and is thus a potential antimicrobial drug target. We recently developed a mass spectrometry-based isotope-coded mass tag (ICMT) labeling method to monitor the real-time solvent-accessible surface of peripheral membrane proteins, such as cholesterol oxidase. The ICMT strategy utilizes maleimide-based isotope tags that covalently react with cysteine residues. In this study, by comparing the ICMT labeling rates of cysteine variants of cholesterol oxidase, we determined which residues of the protein were engaged with the protein-lipid interface. We found that upon addition of cholesterol-containing lipid vesicles, four cysteine residues in a cluster near the substrate entrance channel are labeled more slowly with ICMT probes than in the absence of vesicles, indicating that these four residues were in contact with the membrane surface. From these data, we generated a model of how cholesterol oxidase is oriented when bound to the membrane. In conclusion, this straightforward method, which requires only microgram quantities of protein, offers several advantages over existing methods for the investigation of interfacial membrane proteins and can be applied to a number of different systems.

Immobilization of Cholesterol Oxidase: An Overview

Background:

Cholesterol oxidases are bacterial oxidases widely used commercially for their application in the detection of cholesterol in blood serum, clinical or food samples. Additionally, these enzymes find potential applications as an insecticide, synthesis of anti-fungal antibiotics and a biocatalyst to transform a number of sterol and non-sterol compounds. However, the soluble form of cholesterol oxidases are found to be less stable when applied at higher temperatures, broader pH range, and incur higher costs. These disadvantages can be overcome by immobilization on carrier matrices.

Methods:

This review focuses on the immobilization of cholesterol oxidases on various macro/micro matrices as well as nanoparticles and their potential applications. Selection of appropriate support matrix in enzyme immobilization is of extreme importance. Recently, nanomaterials have been used as a matrix for immobilization of enzyme due to their large surface area and small size. The bio-compatible length scales and surface chemistry of nanoparticles provide reusability, stability and enhanced performance characteristics for the enzyme-nanoconjugates.

Conclusion:

In this review, immobilization of cholesterol oxidase on nanomaterials and other matrices are discussed. Immobilization on nanomatrices has been observed to increase the stability and activity of enzymes. This enhances the applicability of cholesterol oxidases for various industrial and clinical applications such as in biosensors.

Cholesterol-oxidase-magnetic nanobioconjugates for the production of 4-cholesten-3-one and 4-cholesten-3, 7-dione

Cholesterol oxidase(ChOx) enzyme isolated from Pseudomonas aeruginosa PseA(ChOxP) and Rhodococcus erythropolis MTCC 3951(ChOxR) strains as well as a commercial variant produced by Streptomyces sp.(ChOxS) were immobilized on silane modified iron(II, III)oxide magnetic nanoparticles(MNP) by covalent coupling methods. The nanobiocatalysts in case of ChOxP, ChOxR and ChOxS, retained 71, 91 and 86% of cholesterol oxidase activity respectively, as compared to their soluble counterparts. The catalytic efficiency of the immobilized enzymes on nanoparticles was more than 2.0 times higher than the free enzyme. They also showed enhanced pH and thermal stability. After 10 cycles of operation, the MNP-bioconjugates retained 50, 52 and 51% of residual activity in case of ChOxP, ChOxR and ChOxS respectively. The presence of enzyme on nanoparticles was confirmed by FTIR, SEM and TEM. The nanobiocatalysts were used for the biotransformation of cholesterol and 7-ketocholesterol to 4-cholesten-3-one and 4-cholesten-3, 7-dione respectively, which are industrially and medically important steroid precursors.

Extracellular cholesterol oxidase production by Streptomyces aegyptia, in vitro anticancer activities against rhabdomyosarcoma, breast cancer cell-lines and in vivo apoptosis

In recent years, microbial cholesterol oxidases have gained great attention due to its widespread use in medical applications for serum cholesterol determination. Streptomyces aegyptia strain NEAE-102 exhibited high level of extracellular cholesterol oxidase production using a minimum medium containing cholesterol as the sole source of carbon. Fifteen variables were screened using Plackett–Burman design for the enhanced cholesterol oxidase production. The most significant variables affecting enzyme production were further optimized by using the face-centered central composite design. The statistical optimization resulted in an overall 4.97-fold increase (15.631 UmL⁻¹) in cholesterol oxidase production in the optimized medium as compared with the unoptimized medium before applying Plackett Burman design (3.1 UmL⁻¹). The purified cholesterol oxidase was evaluated for its in vitro anticancer activities against five human cancer cell lines. The selectivity index values on rhabdomyosarcoma and breast cancer cell lines were 3.26 and 2.56; respectively. The in vivo anticancer activity of cholesterol oxidase was evaluated against Ehrlich solid tumor model. Compared with control mice, tumors growth was significantly inhibited in the mice injected with cholesterol oxidase alone, doxorubicin alone and cholesterol oxidase/doxorubicin combination by 60.97%, 72.99% and 97.04%; respectively. These results demonstrated that cholesterol oxidase can be used as a promising natural anticancer drug.

Computational insights for the hydride transfer and distinctive roles of key residues in cholesterol oxidase

Cholesterol oxidase (ChOx), a member of the glucose-methanol-choline (GMC) family, catalyzes the oxidation of the substrate via a hydride transfer mechanism and concomitant reduction of the FAD cofactor. Unlike other GMC enzymes, the conserved His447 is not the catalytic base that deprotonates the substrate in ChOx. Our QM/MM MD simulations indicate that the Glu361 residue acts as a catalytic base facilitating the hydride transfer from the substrate to the cofactor. We find that two rationally chosen point mutations (His447Gln and His447Asn) cause notable decreases in the catalytic activity. The binding free energy calculations show that the Glu361 and His447 residues are important in substrate binding. We also performed high-level double-hybrid density functional theory simulations using small model systems, which support the QM/MM MD results. Our work provides a basis for unraveling the substrate oxidation mechanism in GMC enzymes in which the conserved histidine does not act as a base.

Introducing inducible fluorescent split cholesterol oxidase to mammalian cells

Cholesterol oxidase (COase) is a bacterial enzyme catalyzing the first step in the biodegradation of cholesterol. COase is an important biotechnological tool for clinical diagnostics and production of steroid drugs and insecticides. It is also used for tracking intracellular cholesterol; however, its utility is limited by the lack of an efficient temporal control of its activity. To overcome this we have developed a regulatable fragment complementation system for COase cloned from Chromobacterium sp. The enzyme was split into two moieties that were fused to FKBP (FK506-binding protein) and FRB (rapamycin-binding domain) pair and split GFP fragments. The addition of rapamycin reconstituted a fluorescent enzyme, termed split GFP-COase, the fluorescence level of which correlated with its oxidation activity. A rapid decrease of cellular cholesterol induced by intracellular expression of the split GFP-COase promoted the dissociation of a cholesterol biosensor D4H from the plasma membrane. The process was reversible as upon rapamycin removal, the split GFP-COase fluorescence was lost, and cellular cholesterol levels returned to normal. These data demonstrate that the split GFP-COase provides a novel tool to manipulate cholesterol in mammalian cells.

Functional differentiation of 3-ketosteroid Δ1-dehydrogenase isozymes in Rhodococcus ruber strain Chol-4

Background

The Rhodococcus ruber strain Chol-4 genome contains at least three putative 3-ketosteroid Δ¹-dehydrogenase ORFs (kstD1, kstD2 and kstD3) that code for flavoenzymes involved in the steroid ring degradation. The aim of this work is the functional characterization of these enzymes prior to the developing of different biotechnological applications.

Results

The three R. ruber KstD enzymes have different substrate profiles. KstD1 shows preference for 9OHAD and testosterone, followed by progesterone, deoxy corticosterone AD and, finally, 4-BNC, corticosterone and 19OHAD. KstD2 shows maximum preference for progesterone followed by 5α-Tes, DOC, AD testosterone, 4-BNC and lastly 19OHAD, corticosterone and 9OHAD. KstD3 preference is for saturated steroid substrates (5α-Tes) followed by progesterone and DOC. A preliminary attempt to model the catalytic pocket of the KstD proteins revealed some structural differences probably related to their catalytic differences. The expression of kstD genes has been studied by RT-PCR and RT-qPCR. All the kstD genes are transcribed under all the conditions assayed, although an additional induction in cholesterol and AD could be observed for kstD1 and in cholesterol for kstD3. Co-transcription of some correlative genes could be stated. The transcription initiation signals have been searched, both in silico and in vivo. Putative promoters in the intergenic regions upstream the kstD1, kstD2 and kstD3 genes were identified and probed in an apramycin-promoter-test vector, leading to the functional evidence of those R. ruber kstD promoters.

Conclusions

At least three putative 3-ketosteroid Δ¹-dehydrogenase ORFs (kstD1, kstD2 and kstD3) have been identified and functionally confirmed in R. ruber strain Chol-4. KstD1 and KstD2 display a wide range of substrate preferences regarding to well-known intermediaries of the cholesterol degradation pathway (9OHAD and AD) and other steroid compounds. KstD3 shows a narrower substrate range with a preference for saturated substrates. KstDs differences in their catalytic properties was somehow related to structural differences revealed by a preliminary structural modelling. Transcription of R. ruber kstD genes is driven from specific promoters. The three genes are constitutively transcribed, although an additional induction is observed in kstD1 and kstD3. These enzymes have a wide versatility and allow a fine tuning-up of the KstD cellular activity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-017-0657-1) contains supplementary material, which is available to authorized users.

Draft Genome Sequence of the Plant Growth-Promoting Pseudomonas punonensis Strain D1-6 Isolated from the Desert Plant Erodium hirtum in Jordan

Pseudomonas punonensis strain D1-6 was isolated from roots of the desert plant Erodium hirtum, near the Dead Sea in Jordan. The genome of strain D1-6 reveals several key plant growth-promoting and herbicide-resistance genes, indicating a possible specialized role for this endophyte.

Biomedical Applications of Enzymes From Marine Actinobacteria

Marine microbial enzyme technologies have progressed significantly in the last few decades for different applications. Among the various microorganisms, marine actinobacterial enzymes have significant active properties, which could allow them to be biocatalysts with tremendous bioactive metabolites. Moreover, marine actinobacteria have been considered as biofactories, since their enzymes fulfill biomedical and industrial needs. In this chapter, the marine actinobacteria and their enzymes' uses in biological activities and biomedical applications are described.

Draft Genome Sequence of the Plant Growth-Promoting Cupriavidus gilardii Strain JZ4 Isolated from the Desert Plant Tribulus terrestris

We isolated the plant endophytic bacterium Cupriavidus gilardii strain JZ4 from the roots of the desert plant Tribulus terrestris, collected from the Jizan region, Saudi Arabia. We report here the draft genome sequence of JZ4, together with several enzymes related to plant growth-promoting activity, environmental adaption, and antifungal activity.

Modeling and optimization of a continuous bead milling process for bacterial cell lysis using response surface methodology

Schematic representation of the modeling and optimization of continuous bead milling process for efficient bacterial cell lysis.

Purification and Characterization of an Extracellular Cholesterol Oxidase of Bacillus subtilis Isolated from Tiger Excreta

A mesophilic Bacillus sp. initially isolated from tiger excreta and later identified as a Bacillus subtilis strain was used to produce an extracellular cholesterol oxidase (COX) in cholesterol-enriched broth. This bacterial isolate was studied for the production of COX by manipulation of various physicochemical parameters. The extracellular COX was successfully purified from the cell-free culture broth of B. subtilis by successive salting out with ammonium sulfate, dialysis, and riboflavin-affinity chromatography. The purified COX was characterized for its molecular mass/structure and stability. The enzyme possessed some interesting properties such as high native Mr (105 kDa), multimeric (pentamer of ∼21 kDa protein) nature, organic solvent compatibility, and a half-life of ∼2 h at 37 °C. The bacterial COX exhibited ∼22 % higher activity in potassium phosphate buffer (pH 7.5) in the presence of a nonionic detergent Triton X-100 at 0.05 % (v/v). The K m and V max value of COX of B. subtilis COX were found to be 3.25 mM and 2.17 μmol min ml(-1), respectively. The purified COX showed very little cytotoxicity associated with it.

The substrate tolerance of alcohol oxidases

Alcohols are a rich source of compounds from renewable sources, but they have to be activated in order to allow the modification of their carbon backbone. The latter can be achieved via oxidation to the corresponding aldehydes or ketones. As an alternative to (thermodynamically disfavoured) nicotinamide-dependent alcohol dehydrogenases, alcohol oxidases make use of molecular oxygen but their application is under-represented in synthetic biotransformations. In this review, the mechanism of copper-containing and flavoprotein alcohol oxidases is discussed in view of their ability to accept electronically activated or non-activated alcohols and their propensity towards over-oxidation of aldehydes yielding carboxylic acids. In order to facilitate the selection of the optimal enzyme for a given biocatalytic application, the substrate tolerance of alcohol oxidases is compiled and discussed: Substrates are classified into groups (non-activated prim- and sec-alcohols; activated allylic, cinnamic and benzylic alcohols; hydroxy acids; sugar alcohols; nucleotide alcohols; sterols) together with suitable alcohol oxidases, their microbial source, relative activities and (stereo)selectivities.

Electrochemical oxidation of cholesterol

Indirect cholesterol electrochemical oxidation in the presence of various mediators leads to electrophilic addition to the double bond, oxidation at the allylic position, oxidation of the hydroxy group, or functionalization of the side chain. Recent studies have proven that direct electrochemical oxidation of cholesterol is also possible and affords different products depending on the reaction conditions.

Fermented Rhizoma Atractylodis Macrocephalae alleviates high fat diet-induced obesity in association with regulation of intestinal permeability and microbiota in rats

Accumulating evidence suggests the anti-inflammatory and anti-obesity activities of Rhizoma Atractylodis Macrocephalae (RAM). Here, we evaluated the anti-obesity impact of unfermented (URAM) versus fermented RAM (FRAM) using both in vitro and in vivo models. Both URAM and FRAM exhibited marked anti-inflammatory, anti-adipogenic, and anti-obesity activities, and modulation of the gut microbial distribution. However, FRAM, compared to URAM, resulted in more efficient suppression of NO production and normalization of transepithelial electrical resistance in LPS-treated RAW 264.7 and HCT 116 cells, respectively. Compared to URAM, FRAM more effectively reduced the adipose tissue weight; ameliorated the serum triglyceride and aspartate transaminase levels; restored the serum HDL level and intestinal epithelial barrier function in the LPS control group. The relative abundance of Bifidobacterium and Akkermansia as well as Bacteriodetes/Firmicutes ratio in the gut of the LPS control group was significantly enhanced by both URAM and FRAM. However, FRAM, but not URAM, resulted in a significant increase in the distribution of Bacteriodetes and Lactobacillus in the gut of the HFD + LPS group. Our results suggest that FRAM with probiotics can exert a greater anti-obesity effect than URAM, which is probably mediated at least in part via regulation of the intestinal microbiota and gut permeability.

Cholesterol oxidase with high catalytic activity from Pseudomonas aeruginosa: Screening, molecular genetic analysis, expression and characterization

An extracellular cholesterol oxidase producer, Pseudomonas aeruginosa strain PA157, was isolated by a screening method to detect 6β-hydroperoxycholest-4-en-3-one-forming cholesterol oxidase. On the basis of a putative cholesterol oxidase gene sequence in the genome sequence data of P. aeruginosa strain PAO1, the cholesterol oxidase gene from strain PA157 was cloned. The mature form of the enzyme was overexpressed in Escherichia coli cells. The overexpressed enzyme formed inclusion bodies in recombinant E. coli cells grown at 20 °C and 30 °C. A soluble and active PA157 enzyme was obtained when the recombinant cells were grown at 10 °C. The purified enzyme was stable at pH 5.5 to 10 and was most active at pH 7.5-8.0, showing optimal activity at pH 7.0 and 70 °C. The enzyme retained about 90% of its activity after incubation for 30 min at 70 °C. The enzyme oxidized 3β-hydroxysteroids such as cholesterol, β-cholestanol, and β-sitosterol at high rates. The Km value and Vmax value for the cholesterol were 92.6 μM and 15.9 μmol/min/mg of protein, respectively. The Vmax value of the enzyme was higher than those of commercially available cholesterol oxidases. This is the first report to characterize a cholesterol oxidase from P. aeruginosa.

Cloning, expression and biochemical characterization of the cholesterol oxidase CgChoA from Chryseobacterium gleum

BACKGROUND

Cholesterol oxidases are important enzymes for applications such as the analysis of cholesterol in clinical samples, the synthesis of steroid derived drugs, and are considered as potential antibacterial drug targets.

RESULTS

The gene choA encoding a cholesterol oxidase from Chryseobacterium gleum DSM 16776 was cloned into the pQE-30 expression vector and heterologously expressed in Escherichia coli JM109 co-transformed with pRARE2. The N-terminally His-tagged cholesterol oxidase (CgChoA) was assigned to be a monomer in solution by size exclusion chromatography, showed a temperature optimum of 35°C, and a pH optimum at 6.75 using 0.011 M MOPS buffer under the tested conditions. The purified protein showed a maximum activity of 15.5 U/mg. CgChoA showed a Michaelis-Menten like kinetic behavior only when the substrate was dissolved in water and taurocholate (apparent K(m) = 0.5 mM). In addition, the conversion of cholesterol by CgChoA was studied via biocatalytic batches at analytical scale, and cholest-4-en-3-one was confirmed as product by HPLC-MS.

CONCLUSION

CgChoA is a true cholesterol oxidase which activity ranges among the high performing described cholesterol oxidases from other organisms. Thus, the enzyme broadens the available toolbox of cholesterol oxidases for e.g. synthetic and biosensing applications.

Biochemical analysis of recombinant AlkJ from Pseudomonas putida reveals a membrane-associated, flavin adenine dinucleotide-dependent dehydrogenase suitable for the biosynthetic production of aliphatic aldehydes

The noncanonical alcohol dehydrogenase AlkJ is encoded on the alkane-metabolizing alk operon of the mesophilic bacterium Pseudomonas putida GPo1. To gain insight into the enzymology of AlkJ, we have produced the recombinant protein in Escherichia coli and purified it to homogeneity using His6 tag affinity and size exclusion chromatography (SEC). Despite synthesis in the cytoplasm, AlkJ was associated with the bacterial cell membrane, and solubilization with n-dodecyl-β-D-maltoside was necessary to liberate the enzyme. SEC and spectrophotometric analysis revealed a dimeric quaternary structure with stoichiometrically bound reduced flavin adenine dinucleotide (FADH2). The holoenzyme showed thermal denaturation at moderate temperatures around 35°C, according to both activity assay and temperature-dependent circular dichroism spectroscopy. The tightly bound coenzyme was released only upon denaturation with SDS or treatment with urea-KBr and, after air oxidation, exhibited the characteristic absorption spectrum of FAD. The enzymatic activity of purified AlkJ for 1-butanol, 1-hexanol, and 1-octanol as well as the n-alkanol derivative ω-hydroxy lauric acid methyl ester (HLAMe) was quantified in the presence of the artificial electron acceptors phenazine methosulfate (PMS) and 2,6-dichlorophenolindophenol (DCPIP), indicating broad substrate specificity with the lowest activity on the shortest alcohol, 1-butanol. Furthermore, AlkJ was able to accept as cosubstrates/oxidants the ubiquinone derivatives Q0 and Q1, also in conjunction with cytochrome c, which suggests coupling to the bacterial respiratory chain of this membrane-associated enzyme in its physiological environment. Using gas chromatographic analysis, we demonstrated specific biocatalytic conversion by AlkJ of the substrate HLAMe to the industrially relevant aldehyde, thus enabling the biotechnological production of 12-amino lauric acid methyl ester via subsequent enzymatic transamination.

Cholesterol to cholestenone oxidation by ChoG, the main extracellular cholesterol oxidase of Rhodococcus ruber strain Chol-4

The choG ORF of Rhodococcus ruber strain Chol-4 (referred from now as Chol-4) encodes a putative extracellular cholesterol oxidase. In the Chol-4 genome this ORF is located in a gene cluster that includes kstD3 and hsd4B, showing the same genomic context as that found in other Rhodococcus species. The putative ChoG protein is grouped into the class II of cholesterol oxidases, close to the Rhodococcus sp. CECT3014 ChoG homolog. The Chol-4 choG was cloned and expressed in a CECT3014 ΔchoG host strain in order to assess its ability to convert cholesterol into cholestenone. The RT-PCR analysis showed that choG gene was constitutively expressed in all the conditions assayed, but a higher induction could be inferred when cells were growing in the presence of cholesterol. A Chol-4 ΔchoG mutant strain was still able to grow in minimal medium supplemented with cholesterol, although at a slower rate. A comparative study of the removal of both cholesterol and cholestenone from the culture medium of either the wild type Chol-4 or its choG deletion mutant revealed a major role of ChoG in the extracellular production of cholestenone from cholesterol and, therefore, this enzyme may be related with the maintenance of a convenient supply of cholestenone for the succeeding steps of the catabolic pathway.