Cholesterol oxidase: structure and function

Surface-Enhanced Raman Scattering Active Core-Shell Ag NPs@Carbon Dots with Enzyme-Mimicking Activities for Label-Free Measurement Cholesterol

Serological-sensitive testing of cholesterol holds significant value in the fields of healthcare and clinical diagnosis. This study reports on the preparation of peroxidase-mimicking nanozymes through the wrapping of N, S-doped carbon dots (DCDs) on the surface of silver nanoparticles (Ag NPs@DCD). The shell-core structure of Ag NPs@DCD displays peroxidase-mimicking capability, with the potential to catalyze inactive Raman probe molecules into the Raman reporters. Furthermore, a "shell-isolated nanoparticles-enhanced Raman spectroscopy" structure exhibited an enhanced Raman signal of reporter molecules. Ag NPs@DCD were utilized to create a label-free SERS sensing system for high-performance detection of cholesterol in serum samples. These results demonstrate the potential of the novel nanozyme-based SERS approach for clinical diagnosis.

Novel mechanism of hydrogen peroxide for promoting efficient natamycin synthesis in Streptomyces

The mechanism of regulation of natamycin biosynthesis by Streptomyces in response to oxidative stress is unclear. Here, we first show cholesterol oxidase SgnE, which catalyzes the formation of H2O2 from sterols, triggered a series of redox-dependent interactions to stimulate natamycin production in S. gilvosporeus. In response to reactive oxygen species, residues Cys212 and Cys221 of the H2O2-sensing consensus sequence of OxyR were oxidized, resulting in conformational changes in the protein: OxyR extended its DNA-binding domain to interact with four motifs of promoter p sgnM . This acted as a redox-dependent switch to turn on/off gene transcription of sgnM, which encodes a cluster-situated regulator, by controlling the affinity between OxyR and p sgnM , thus regulating the expression of 12 genes in the natamycin biosynthesis gene cluster. OxyR cooperates with SgnR, another cluster-situated regulator and an upstream regulatory factor of SgnM, synergistically modulated natamycin biosynthesis by masking/unmasking the -35 region of p sgnM depending on the redox state of OxyR in response to the intracellular H2O2 concentration. IMPORTANCE Cholesterol oxidase SgnE is an indispensable factor, with an unclear mechanism, for natamycin biosynthesis in Streptomyces. Oxidative stress has been attributed to the natamycin biosynthesis. Here, we show that SgnE catalyzes the formation of H2O2 from sterols and triggers a series of redox-dependent interactions to stimulate natamycin production in S. gilvosporeus. OxyR, which cooperates with SgnR, acted as a redox-dependent switch to turn on/off gene transcription of sgnM, which encodes a cluster-situated regulator, by masking/unmasking its -35 region, to control the natamycin biosynthesis gene cluster. This work provides a novel perspective on the crosstalk between intracellular ROS homeostasis and natamycin biosynthesis. Application of these findings will improve antibiotic yields via control of the intracellular redox pressure in Streptomyces.

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.

Development of a novel spatiotemporal depletion system for cellular cholesterol

Cholesterol is an essential component of mammalian cell membranes whose subcellular concentration and function are tightly regulated by de novo biosynthesis, transport, and storage. Although recent reports have suggested diverse functions of cellular cholesterol in different subcellular membranes, systematic investigation of its site-specific roles has been hampered by the lack of a methodology for spatiotemporal manipulation of cellular cholesterol levels. Here, we report the development of a new cholesterol depletion system that allows for spatiotemporal manipulation of intracellular cholesterol levels. This system utilizes a genetically encoded cholesterol oxidase whose intrinsic membrane binding activity is engineered in such a way that its membrane targeting can be controlled in a spatiotemporally specific manner via chemically induced dimerization. In combination with in situ quantitative imaging of cholesterol and signaling activity measurements, this system allows for unambiguous determination of site-specific functions of cholesterol in different membranes, including the plasma membrane and the lysosomal membrane.

Cytotoxic activity of cholesterol oxidase produced by Streptomyces sp. AKHSS against cancerous cell lines: mechanism of action in HeLa cells

Re-occurrence of cancer is the major drawback for the currently available anticancer therapies. Therefore, study of an efficient enzyme, cholesterol oxidase produced by various kinds of microbes especially obtained from unexplored marine actinobacterial species against human cancer cell lines and understanding its mechanism of action helps to identify an irreversible and potent anticancer agent. The cytotoxic potential of cholesterol oxidase produced by a marine Streptomyces sp. AKHSS against four different human cancer cell lines was demonstrated through MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide] assay. Fluorescent confocal microscopy and flow cytometry based experiments were performed to understand the efficiency of the enzymatic action on HeLa cells. Further, the apoptotic related proteins were detected through western blotting. Interestingly, the enzyme exhibited potent cytotoxicity at very low concentrations (0.093-0.327 µM) against all the cells tested. Fluorescent confocal microscopy revealed the morphological variations induced by the enzyme on cancer cell lines such as the formation of lipid droplets and condensation of nuclei. The enzyme treated cell-free extracts of HeLa cells analyzed through gas chromatography mass spectrometry showed the depletion of membrane cholesterol and the presence of substituted enzyme oxidized product, cholest-4-ene-3-one. The enzyme had induced significant inhibitory effects on the cell viability such as cell cycle arrest (G₁ phase), apoptosis and rise of reactive oxygen species as evident through flow cytometry. Besides, hyperpolarization of mitochondrial membrane, reduced rates of phosphorylation of pAkt and the expression of apoptotic death markers like Fas, Fas L, caspases (8 and 3) and PARP-1 were recorded in the enzyme treated HeLa cells. Thus, cholesterol oxidase purified from a marine Streptomyces sp. AKHSS exhibits potent cytotoxicity at very low concentrations against human cancer cell lines. All the ex vivo experiments portrayed the substantial inhibitory effect of the enzyme on HeLa cells suggesting that cholesterol oxidase of Streptomyces sp. AKHSS could be a prominent cancer chemotherapeutic agent.

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.

Mycobacterium tuberculosis Requires Cholesterol Oxidase to Disrupt TLR2 Signalling in Human Macrophages

This study tested the hypothesis that Mycobacterium tuberculosis (Mtb) uses a cholesterol oxidase enzyme (ChoD) to suppress a toll-like receptor type 2- (TLR2-) dependent signalling pathway to modulate macrophages' immune response. We investigated the impact of Mtb possessing or lacking ChoD as well as TBChoD recombinant protein obtained from Mtb on the expression and activation of two key intracellular proteins involved in TLR2 signalling in human macrophages. Finally, the involvement of TLR2-related signalling proteins in an inflammatory/immunosuppressive response of macrophages to Mtb was evaluated. We demonstrate that wild-type Mtb but not the ∆choD mutant decreased the cytosolic IRAK4 and TRAF6 protein levels while strongly enhancing IRAK4 and TRAF6 mRNA levels in macrophages. Our data show that the TLR2 present on the surface of macrophages are involved in disturbing the signalling pathway by wild-type Mtb. Moreover, recombinant TBChoD effectively decreased the cytosolic level of TRAF6 and lowered the phosphorylation of IRAK4, which strongly confirm an involvement of cholesterol oxidase in affecting the TLR2-related pathway by Mtb. Wild-type Mtb induced an immunosuppressive response of macrophages in an IRAK4- and TRAF6-dependent manner as measured by interleukin 10 production. In conclusion, ChoD is a virulence factor that enables Mtb to disturb the TLR2-related signalling pathway in macrophages and modulate their response.

Identification, function, and application of 3-ketosteroid Δ1-dehydrogenase isozymes in Mycobacterium neoaurum DSM 1381 for the production of steroidic synthons

Background

3-Ketosteroid-Δ1-dehydrogenase (KstD) is a key enzyme in the metabolic pathway for chemical modifications of steroid hormones. Only a few KstDs have thus far been characterized biochemically and applied for the production of steroidal pharmaceutical intermediates. Three KstDs, KstD1, KstD2, and KstD3, were identified in Mycobacterium neoaurum DSM 1381, and they shared up to 99, 85 and 97% amino acid identity with previously reported KstDs, respectively. In this paper, KstDs from M. neoaurum DSM 1381 were investigated and exemplified their potential application for industrial steroid transformation.

Results

The recombinant KstD2 from Bacillus subtilis exhibited higher enzymatic activity when 4-androstene-3,17-dione (AD) and 22-hydroxy-23, 24-bisnorchol-4-ene-3-one (4HP) were used as the substrates, and resulted in specific activities of 22.40 and 19.19 U mg⁻¹, respectively. However, the specific activities of recombinant KstD2 from Escherichia coli, recombinant KstD1 from B. subtilis and E. coli, and recombinant KstD3, also fed with AD and 4HP, had significantly lower specific activities. We achieved up to 99% bioconversion rate of 1,4-androstadiene-3,17-dione (ADD) from 8 g L⁻¹ AD after 15 h of fermentation using E. coli transformant BL21-kstD2. And in vivo transcriptional analysis revealed that the expression of kstD1 in M. neoaurum DSM 1381 increased by 60.5-fold with phytosterols as the substrate, while the mRNA levels of kstD2 and kstD3 were bearly affected by the phytosterols. Therefore, we attempted to create a 4HP producing strain without kstD1, which could covert 20 g L⁻¹ phytosterols to 14.18 g L⁻¹ 4HP.

Conclusions

In vitro assay employing the recombinant enzymes revealed that KstD2 was the most promising candidate for biocatalysis in biotransformation of AD. However, in vivo analysis showed that the cellular regulation of kstD1 was much more active than those of the other kstDs in response to the presence of phytosterols. Based on the findings above, we successfully constructed E. coli transformant BL21-kstD2 for ADD production from AD and M. neoaurum DSM 1381 ΔkstD1 strain for 4HP production using phytosterols as the substrate.

Electronic supplementary material

The online version of this article (10.1186/s12934-018-0916-9) contains supplementary material, which is available to authorized users.

Membrane cholesterol depletion as a trigger of Nav1.9 channel-mediated inflammatory pain

Cholesterol is a major lipid component of the mammalian plasma membrane. While much is known about its metabolism, its transport, and its role in atherosclerotic vascular disease, less is known about its role in neuronal pathophysiology. This study reveals an unexpected function of cholesterol in controlling pain transmission. We show that inflammation lowers cholesterol content in skin tissue and sensory DRG culture. Pharmacological depletion of cellular cholesterol entails sensitization of nociceptive neurons and promotes mechanical and thermal hyperalgesia through the activation of voltage-gated Nav1.9 channels. Inflammatory mediators enhance the production of reactive oxygen species and induce partitioning of Nav1.9 channels from cholesterol-rich lipid rafts to cholesterol-poor non-raft regions of the membrane. Low-cholesterol environment enhances voltage-dependent activation of Nav1.9 channels leading to enhanced neuronal excitability, whereas cholesterol replenishment reversed these effects. Consistently, we show that transcutaneous delivery of cholesterol alleviates hypersensitivity in animal models of acute and chronic inflammatory pain. In conclusion, our data establish that membrane cholesterol is a modulator of pain transmission and shed a new light on the relationship between cholesterol homeostasis, inflammation, and pain.

Computational site-directed mutagenesis studies of the role of the hydrophobic triad on substrate binding in cholesterol oxidase

Cholesterol oxidase (ChOx) is a flavoenzyme that oxidizes and isomerizes cholesterol (CHL) to form cholest-4-en-3-one. Molecular docking and molecular dynamics simulations were conducted to predict the binding interactions of CHL in the active site. Several key interactions (E361-CHL, N485-FAD, and H447-CHL) were identified and which are likely to determine the correct positioning of CHL relative to flavin-adenine dinucleotide (FAD). Binding of CHL also induced changes in key residues of the active site leading to the closure of the oxygen channel. A group of residues, Y107, F444, and Y446, known as the hydrophobic triad, are believed to affect the binding of CHL in the active site. Computational site-directed mutagenesis of these residues revealed that their mutation affects the conformations of key residues in the active site, leading to non-optimal binding of CHL and to changes in the structure of the oxygen channel, all of which are likely to reduce the catalytic efficiency of ChOx. Proteins 2017; 85:1645-1655. © 2017 Wiley Periodicals, Inc.

C4b-binding Protein Protects β-Cells from Islet Amyloid Polypeptide-induced Cytotoxicity

C4BP (C4b-binding protein) is a polymer of seven identical α chains and one unique β chain synthesized in liver and pancreas. We showed previously that C4BP enhances islet amyloid polypeptide (IAPP) fibril formation in vitro Now we report that polymeric C4BP strongly inhibited lysis of human erythrocytes incubated with monomeric IAPP, whereas no lysis was observed after incubation with preformed IAPP fibrils. In contrast, incubation with the monomeric α-chain of C4BP was less effective. These data indicate that polymeric C4BP with multiple binding sites for IAPP neutralizes lytic activity of IAPP. Furthermore, addition of monomeric IAPP to a rat insulinoma cell line (INS-1) resulted in decreased cell viability, which was restored in the presence of physiological concentrations of C4BP. Treatment of INS-1 cells and primary rat islets with IAPP also diminished their ability to secrete insulin upon stimulation with glucose, which was reversed in the presence of C4BP. Further, C4BP was internalized together with IAPP into INS-1 cells. Pathway analyses of mRNA expression microarray data indicated that cells exposed to C4BP and IAPP in comparison with IAPP alone increased expression of genes involved in cholesterol synthesis. Depletion of cholesterol through methyl-β-cyclodextrin or cholesterol oxidase abolished the protective effect of C4BP on IAPP cytotoxicity of INS-1 cells. Also, inhibition of phosphoinositide 3-kinase but not NF-κB had a similar effect. Taken together, C4BP protects β-cells from IAPP cytotoxicity by modulating IAPP fibril formation extracellularly and also, after uptake by the cells, by enhancing cholesterol synthesis.

Production and characterization of recombinant perdeuterated cholesterol oxidase

Cholesterol oxidase (CO) is a FAD (flavin adenine dinucleotide) containing enzyme that catalyzes the oxidization and isomerization of cholesterol. Studies directed toward elucidating the catalytic mechanism of CO will provide an important general understanding of Flavin-assisted redox catalysis. Hydrogen atoms play an important role in enzyme catalysis; however, they are not readily visualized in protein X-ray diffraction structures. Neutron crystallography is an ideal method for directly visualizing hydrogen positions at moderate resolutions because hydrogen and deuterium have comparable neutron scattering lengths to other heavy atoms present in proteins. The negative coherent and large incoherent scattering lengths of hydrogen atoms in neutron diffraction experiments can be circumvented by replacing hydrogen atoms with its isotope, deuterium. The perdeuterated form of CO was successfully expressed from minimal medium, purified, and crystallized. X-ray crystallographic structures of the enzyme in the perdeuterated and hydrogenated states confirm that there are no apparent structural differences between the two enzyme forms. Kinetic assays demonstrate that perdeuterated and hydrogenated enzymes are functionally identical. Together, structural and functional studies indicate that the perdeuterated protein is suitable for structural studies by neutron crystallography directed at understanding the role of hydrogen atoms in enzyme catalysis.

Cholesterol oxidase binds TLR2 and modulates functional responses of human macrophages

Cholesterol oxidase (ChoD) is considered to be an important virulence factor for Mycobacterium tuberculosis (Mtb), but its influence on macrophage activity is unknown. Here we used Nocardia erythropolis ChoD, which is very similar to the Mtb enzyme (70% identity at the amino-acid level), to evaluate the impact of bacterial ChoD on the activity of THP-1-derived macrophages in vitro. We found that ChoD decreased the surface expression of Toll-like receptor type 2 (TLR2) and complement receptor 3 (CR3) on these macrophages. Flow cytometry and confocal microscopy showed that ChoD competed with lipoteichoic acid for ligand binding sites on TLR2 but not on CR3, suggesting that ChoD signaling is mediated via TLR2. Binding of ChoD to the membrane of macrophages had diverse effects on the activity of macrophages, activating p38 mitogen activated kinase and stimulating production of a large amount of interleukin-10. Moreover, ChoD primed macrophages to enhance the production of reactive oxygen species in response to the phorbol myristate acetate, which was reduced by "switching off" TLR-derived signaling through interleukin-1 receptor-associated kinases 1 and 4 inhibition. Our study revealed that ChoD interacts directly with macrophages via TLR2 and influences the biological activity of macrophages during the development of the initial response to infection.

Deciphering the transcriptional regulation of cholesterol catabolic pathway in mycobacteria: identification of the inducer of KstR repressor

Cholesterol degradation plays a prominent role in Mycobacterium tuberculosis infection; therefore, to develop new tools to combat this disease, we need to decipher the components comprising and regulating the corresponding pathway. A TetR-like repressor (KstR) regulates the upper part of this complex catabolic pathway, but the induction mechanism remains unknown. Using a biophysical approach, we have discovered that the inducer molecule of KstR in M. smegmatis mc(2)155 is not cholesterol but 3-oxo-4-cholestenoic acid, one of the first metabolic intermediates. Binding this compound induces dramatic conformational changes in KstR that promote the KstR-DNA interaction to be released from the operator, retaining its dimeric state. Our findings suggest a regulatory model common to all cholesterol degrading bacteria in which the first steps of the pathway are critical to its mineralization and explain the high redundancy of the enzymes involved in these initial steps.

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.

Cholesterol oxidase is indispensable in the pathogenesis of Mycobacterium tuberculosis

Despite considerable research effort, the molecular mechanisms of Mycobacterium tuberculosis (Mtb) virulence remain unclear. Cholesterol oxidase (ChoD), an extracellular enzyme capable of converting cholesterol to its 3-keto-4-ene derivative, cholestenone, has been proposed to play a role in the virulence of Mtb. Here, we verified the hypothesis that ChoD is capable of modifying the bactericidal and pro-inflammatory activity of human macrophages. We also sought to determine the contribution of complement receptor 3 (CR3)- and Toll-like receptor 2 (TLR2)-mediated signaling pathways in the development of macrophage responses to Mtb. We found that intracellular replication of an Mtb mutant lacking a functional choD gene (ΔchoD) was less efficient in macrophages than that of the wild-type strain. Blocking CR3 and TLR2 with monoclonal antibodies enhanced survival of ΔchoD inside macrophages. We also showed that, in contrast to wild-type Mtb, the ΔchoD strain induced nitric oxide production in macrophages, an action that depended on the TLR2, but not the CR3, signaling pathway. Both wild-type and mutant strains inhibited the production of reactive oxygen species (ROS), but the ΔchoD strain did so to a significantly lesser extent. Blocking TLR2-mediated signaling abolished the inhibitory effect of wild-type Mtb on ROS production by macrophages. Wild-type Mtb, but not the ΔchoD strain, decreased phorbol myristate acetate-induced phosphorylation of extracellular signal-regulated kinases 1 and 2 (ERK1/2), which are involved in both TLR2- and CR3-mediated signaling pathways. Our finding also revealed that the production of interleukin 10 by macrophages was significantly lower in ΔchoD-infected macrophages than in wild-type Mtb-infected macrophages. However, tumor necrosis factor-α production by macrophages was the same after infection with mutant or wild-type strains. In summary, we demonstrate here that ChoD is required for Mtb interference with the TLR2-mediated signaling pathway and subsequent intracellular growth and survival of the pathogen in human macrophages.

Improvement of the thermostability and enzymatic activity of cholesterol oxidase by site-directed mutagenesis

Site-directed mutagenesis was applied to enhance the thermostability and enzymatic activity of cholesterol oxidase (ChOx) isolated from Brevibacterium sp. Three amino acid residues (Q153E, F128L, and S143H) located near the FAD-binding site of the enzyme were substituted based on structural analysis. The specific activity of the two-sites mutant Q153E/F128L increased by 11.6% and the relative activity increased by 47% when grown for 2 h at 50 °C. This mutant is a potential industrial strain for producing ChOx.