Overexpression, one-step purification, and characterization of a type II cholesterol oxidase from a local isolate Rhodococcus sp. PTCC 1633

Temperature-resistant and solvent-tolerant lipases as industrial biocatalysts: Biotechnological approaches and applications

The development of new biocatalytic systems to replace the chemical catalysts, with suitable characteristics in terms of efficiency, stability under high temperature reactions and in the presence of organic solvents, reusability, and eco-friendliness is considered a very important step to move towards the green processes. From this basis, the use of lipase as a catalyst is highly desired for many industrial applications because it offers the reactions in which could be used, stability in harsh conditions, reusability and a greener process. Therefore, the introduction of temperature-resistant and solvent-tolerant lipases have become essential and ideal for industrial applications. Temperature-resistant and solvent-tolerant lipases have been involved in many large-scale applications including biodiesel, detergent, food, pharmaceutical, organic synthesis, biosensing, pulp and paper, textile, animal feed, cosmetics, and leather industry. So, the present review provides a comprehensive overview of the industrial use of lipase. Moreover, special interest in biotechnological and biochemical techniques for enhancing temperature-resistance and solvent-tolerance of lipases to be suitable for the industrial uses.

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.

Production of recombinant cholesterol oxidase containing covalently bound FAD in Escherichia coli

Background

Cholesterol oxidase is an alcohol dehydrogenase/oxidase flavoprotein that catalyzes the dehydrogenation of C(3)-OH of cholesterol. It has two major biotechnological applications, i.e. in the determination of serum (and food) cholesterol levels and as biocatalyst providing valuable intermediates for industrial steroid drug production. Cholesterol oxidases of type I are those containing the FAD cofactor tightly but not covalently bound to the protein moiety, whereas type II members contain covalently bound FAD. This is the first report on the over-expression in Escherichia coli of type II cholesterol oxidase from Brevibacterium sterolicum (BCO).

Results

Design of the plasmid construct encoding the mature BCO, optimization of medium composition and identification of the best cultivation/induction conditions for growing and expressing the active protein in recombinant E. coli cells, concurred to achieve a valuable improvement: BCO volumetric productivity was increased from ~500 up to ~25000 U/L and its crude extract specific activity from 0.5 up to 7.0 U/mg protein. Interestingly, under optimal expression conditions, nearly 55% of the soluble recombinant BCO is produced as covalently FAD bound form, whereas the protein containing non-covalently bound FAD is preferentially accumulated in insoluble inclusion bodies.

Conclusions

Comparison of our results with those published on non-covalent (type I) COs expressed in recombinant form (either in E. coli or Streptomyces spp.), shows that the fully active type II BCO can be produced in E. coli at valuable expression levels. The improved over-production of the FAD-bound cholesterol oxidase will support its development as a novel biotool to be exploited in biotechnological applications.