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

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.

Current Trends and Perspectives in Microbial Bioconversions of Steroids

The microbiological transformation of sterols is currently the technological basis for the industrial production of valuable steroid precursors, the so-called synthons, from which a wide range of steroid and indane isoprenoids are obtained by combined chemical and enzymatic routes. These compounds include value-added corticoids, neurosteroids, sex hormones, bile acids, and other terpenoid lipids required by the medicine, pharmaceutical, food, veterinary, and agricultural industries.Progress in understanding the molecular mechanisms of microbial degradation of steroids, and the development and implementation of genetic technologies, opened a new era in steroid biotechnology. Metabolic engineering of microbial producers makes it possible not only to improve the biocatalytic properties of industrial strains by enhancing their target activity and/or suppressing undesirable activities in order to avoid the formation of by-products or degradation of the steroid core, but also to redirect metabolic fluxes in cells towards accumulation of new metabolites that may be useful for practical applications. Along with whole-cell catalysis, the interest of researchers is growing in enzymatic methods that make it possible to carry out selective structural modifications of steroids, such as the introduction of double bonds, the oxidation of steroidal alcohols, or the reduction of steroid carbonyl groups. A promising area of research is strain engineering based on the heterologous expression of foreign steroidogenesis systems (bacterial, fungal, or mammalian) that ensure selective formation of demanded hydroxylated steroids.Here, current trends and progress in microbial steroid biotechnology over the past few years are briefly reviewed, with a particular focus on the application of metabolic engineering and synthetic biology techniques to improve existing and create new whole-cell microbial biocatalysts.

Heterologous expression, molecular studies and biochemical characterization of a novel alkaline esterase gene from Bacillus thuringiensis for detergent industry

Present study was aimed to clone and express the esterase encoding gene from Bacillus thuringiensis in E. coli BL21. Purification of recombinant esterase enzyme was achieved up to 48.6 purification folds by ion exchange chromatography with specific activity of 126.36 U mg^-1. Molecular weight of esterase enzyme was 29 kDa as measured by SDS-PAGE. Purified esterase enzyme showed stability up to 90% at 90 °C and remained stable in a wide pH range (8-11). Molecular docking strengthens the experimental results by showing the higher binding energy with p-NP-butyrate. Enzyme activity was found to be reduced by EDTA but enhanced in the presence of other metal ions. Enzyme activity was reduced with 1% SDS, PMSF, and urea but organic solvents did not show considerable impact on it even at higher concentrations. Purified recombinant esterase was also found to be compatible with commercial laundry detergents and showed very good stability (up to 90%). All these properties proved the esterase enzyme from B. thuringensis a significant addition in detergent industry.

Expression of Codon-Optimized Gene Encoding Murine Moloney Leukemia Virus Reverse Transcriptase in Escherichia coli

Moloney murine leukemia virus reverse transcriptase (MMLV-RT) is the most frequently used enzyme in molecular biology for cDNA synthesis. To date, reverse transcription coupled with Polymerase Chain Reaction, known as RT-PCR, has been popular as an excellent approach for the detection of SARS-CoV-2 during the COVID-19 pandemic. In this study, we aimed to improve the enzymatic production and performance of MMLV-RT by optimizing both codon and culture conditions in E. coli expression system. By applying the optimized codon and culture conditions, the enzyme was successfully overexpressed and increased at high level based on the result of SDS-PAGE and Western blotting. The total amount of MMLV-RT has improved 85-fold from 0.002 g L^-1 to 0.175 g L^-1 of culture. One-step purification by nickel affinity chromatography has been performed to generate the purified enzyme for further analysis of qualitative and quantitative RT activity. Overall, our investigation provides useful strategies to enhance the recombinant enzyme of MMLV-RT in both production and performance. More importantly, the enzyme has shown promising activity to be used for RT-PCR assay.

Enzymatic hydrolysis of lignocellulosic biomass using a novel, thermotolerant recombinant xylosidase enzyme from Clostridium clariflavum: a potential addition for biofuel industry

The present study describes the cloning, expression, purification and characterization of the xylosidase gene (1650 bp) from a thermophilic bacterium Clostridium clariflavum into E. coli BL21 (DE3) using the expression vector pET-21a(+) for utilization in biofuel production. The recombinant xylosidase enzyme was purified to homogeneity by heat treatment and immobilized metal ion affinity chromatography. SDS-PAGE determined that the molecular weight of purified xylosidase was 60 kDa. This purified recombinant xylosidase showed its maximum activity at a temperature of 37 °C and pH 6.0. The purified recombinant xylosidase enzyme remains stable up to 90 °C for 4 h and retained 54.6% relative activity as compared to the control. The presence of metal ions such as Ca²⁺ and Mg²⁺ showed a positive impact on xylosidase enzyme activity whereas Cu²⁺ and Hg²⁺ inhibit its activity. Organic solvents did not considerably affect the stability of the purified xylosidase enzyme while DMSO and SDS cause the inhibition of enzyme activity. Pretreatment experiments were run in triplicate for 72 h at 30 °C using 10% NaOH. Saccharification experiment was performed by using 1% substrate (pretreated plant biomass) in citrate phosphate buffer of pH 6.5 loaded with 150 U mL⁻¹ of purified recombinant xylosidase enzyme along with ampicillin (10  μg mL⁻¹). Subsequent incubation was carried out at 50 °C and 100 rpm in a shaking incubator for 24 h. Saccharification potential of the recombinant xylosidase enzyme was calculated against both pretreated and untreated sugarcane bagasse and wheat straw as 9.63% and 8.91% respectively. All these characteristics of the recombinant thermotolerant xylosidase enzyme recommended it as a potential candidate for biofuel industry.

The present study describes the cloning, expression, purification and characterization of a xylosidase gene from Clostridium clariflavum into E. coli BL21 (DE3) using the expression vector pET-21a(+) for utilization in biofuel production.

Optimization of an Inclusion Body-Based Production of the Influenza Virus Neuraminidase in Escherichia coli

Neuraminidase (NA), as an important protein of influenza virus, represents a promising target for the development of new antiviral agents for the treatment and prevention of influenza A and B. Bacterial host strain Escherichia coli BL21 (DE3)pLysS containing the NA gene of the H1N1 influenza virus produced this overexpressed enzyme in the insoluble fraction of cells in the form of inclusion bodies. The aim of this work was to investigate the effect of independent variables (propagation time, isopropyl β-d-1-thiogalactopyranoside (IPTG) concentration and expression time) on NA accumulation in inclusion bodies and to optimize these conditions by response surface methodology (RSM). The maximum yield of NA (112.97 ± 2.82 U/g) was achieved under optimal conditions, namely, a propagation time of 7.72 h, IPTG concentration of 1.82 mM and gene expression time of 7.35 h. This study demonstrated that bacterially expressed NA was enzymatically active.

An Esterase with Increased Acetone Tolerance from Bacillus subtilis E9 over Expressed in E. coli BL21 Using pTac Bs-est Vector

Bacillus subtilis E9 was identified as a potential strain producing esterase. The gene coding esterase from B. subtilis E9 was amplified using esterase-specific primers and the sequence was translated in silico. The presence of conserved catalytic triad amino acid residues (His-Ser-Asp/Glu) confirmed the functional nature of the esterase enzyme. Docking studies conducted with modeled protein and the ligand p-nitrophenyl acetate showed that the amino acid residues interacting with the ligand were Ser77, His76, and Gly103. The gene coding for esterase from B. subtilis E9 was cloned into an assembled vector having Tac promoter (pTac), pUC origin of replication, Ni-Histidine residues, ampicillin cassette, and T7 terminator using Golden gate DNA assembly method. The generated pTac Bs-est (4598 bp) recombinant plasmid was transformed and heterologously expressed in Escherichia coli BL21 (DE3) strain. The tagged recombinant protein was purified to yield 43.4% pure protein with specific activity of 772 U/mg. The purified recombinant protein was subjected to peptide sequencing and the identity was confirmed as esterase by peptide tandem mass fragmentation method using the LC-MS/MS analysis. The purified recombinant esterase was found to be organic solvent stable and tolerant up to 5 days retaining around 95% residual activity in 30-90% v/v Acetone. The recombinant esterase expressed in our study was found to exhibit better organic solvent stability and tolerance than compared to the original bacterial esterase from B. subtilis E9, a property which could be explored in the biocatalytic and synthetic transformation reactions for industrial applications.

A prokaryote system optimization for rMEPLox expression: A promising non-toxic antigen for Loxosceles antivenom production

Loxoscelism is the most dangerous araneism form in Brazil and antivenom therapy is the recommended treatment. Antivenom is produced by horse immunization with Loxosceles spider venom, which is toxic for the producer animal. Moreover, due to the high amount of venom required for horse hyperimmunization, new strategies for antigens obtention have been proposed. In this sense, our research group has previously produced a non-toxic recombinant multiepitopic protein derived from Loxosceles toxins (rMEPLox). rMEPLox was a successful immunogen, being able to induce the production of neutralizing antibodies, which could be used in the Loxoscelism treatment. However, rMEPLox obtention procedure requires optimization, as its production needs to be scaled up to suit antivenom manufacture. Therefore, an effective protocol development for rMEPlox production would be advantageous. To achieve this objective, we evaluated the influence of different cultivation conditions for rMEPLox optimum expression. The optimum conditions to obtain large amounts of rMEPlox were defined as the use of C43(DE3)pLysS as a host strain, 2xTY medium, 0.6 mM IPTG, biomass pre induction of OD600nm = 0.4 and incubation at 30 °C for 16 h. Following the optimized protocol, 39.84 mg/L of soluble rMEPLox was obtained and tested as immunogen. The results show that the obtained rMEPLox preserved the previously described immunogenicity, and it was able to generate antibodies that recognize different epitopes of the main Loxosceles venom toxins, which makes it a promising candidate for the antivenom production for loxoscelism treatment.

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.

Escherichia coli expression and characterization of α-amylase from Geobacillus thermodenitrificans DSM-465

Alpha amylase, catalyzing the hydrolysis of starch is a ubiquitous enzyme with tremendous industrial applications. A 1698 bp gene coding for 565 amino acid amylase was PCR amplified from Geobacillus thermodenitrificans DSM-465, cloned in pET21a (+) plasmid, expressed in BL21 (DE3) strain of E. coli and characterized. The recombinant enzyme exhibited molecular weight of 63 kDa, optimum pH 8, optimum temperature 70°C, and KM value of 157.7µM. On pilot scale, the purified enzyme efficiently removed up to 95% starch from the cotton fabric indicating its desizing ability at high temperature. 3D model of enzyme built by Raptor-X and validated by Ramachandran plot appeared as a monomer having 31% α-helices, 15% β-sheets, and 52% loops. Docking studies have shown the best binding affinity of enzyme with amylopectin (∆G -10.59). According to our results, Asp 232, Glu274, Arg448, Glu385, Asp34, Asn276, and Arg175 constitute the potential active site of enzyme.

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.