Adrenodoxin: structure, stability, and electron transfer properties

Activation of Coq6p, a FAD Monooxygenase Involved in Coenzyme Q Biosynthesis, by Adrenodoxin Reductase/Ferredoxin

Adrenodoxin reductase (AdxR) plays a pivotal role in electron transfer, shuttling electrons between NADPH and iron/sulfur adrenodoxin proteins in mitochondria. This electron transport system is essential for P450 enzymes involved in various endogenous biomolecules biosynthesis. Here, we present an in-depth examination of the kinetics governing the reduction of human AdxR by NADH or NADPH. Our results highlight the efficiency of human AdxR when utilizing NADPH as a flavin reducing agent. Nevertheless, akin to related flavoenzymes such as cytochrome P450 reductase, we observe that low NADPH concentrations hinder flavin reduction due to intricate equilibrium reactions between the enzyme and its substrate/product. Remarkably, the presence of MgCl2 suppresses this complex kinetic behavior by decreasing NADPH binding to oxidized AdxR, effectively transforming AdxR into a classical Michaelis-Menten enzyme. We propose that the addition of MgCl2 may be adapted for studying the reductive half-reactions of other flavoenzymes with NADPH. Furthermore, in vitro experiments provide evidence that the reduction of the yeast flavin monooxygenase Coq6p relies on an electron transfer chain comprising NADPH-AdxR-Yah1p-Coq6p, where Yah1p shuttles electrons between AdxR and Coq6p. This discovery explains the previous in vivo observation that Yah1p and the AdxR homolog, Arh1p, are required for the biosynthesis of coenzyme Q in yeast.

FDX1 regulates cellular protein lipoylation through direct binding to LIAS

Ferredoxins are a family of iron-sulfur (Fe-S) cluster proteins that serve as essential electron donors in numerous cellular processes that are conserved through evolution. The promiscuous nature of ferredoxins as electron donors enables them to participate in many metabolic processes including steroid, heme, vitamin D, and Fe-S cluster biosynthesis in different organisms. However, the unique natural function(s) of each of the two human ferredoxins (FDX1 and FDX2) are still poorly characterized. We recently reported that FDX1 is both a crucial regulator of copper ionophore-induced cell death and serves as an upstream regulator of cellular protein lipoylation, a mitochondrial lipid-based post-translational modification naturally occurring on four mitochondrial enzymes that are crucial for TCA cycle function. Here we show that FDX1 directly regulates protein lipoylation by binding the lipoyl synthase (LIAS) enzyme promoting its functional binding to the lipoyl carrier protein GCSH and not through indirect regulation of cellular Fe-S cluster biosynthesis. Metabolite profiling revealed that the predominant cellular metabolic outcome of FDX1 loss of function is manifested through the regulation of the four lipoylation-dependent enzymes ultimately resulting in loss of cellular respiration and sensitivity to mild glucose starvation. Transcriptional profiling established that FDX1 loss-of-function results in the induction of both compensatory metabolism-related genes and the integrated stress response, consistent with our findings that FDX1 loss-of-function is conditionally lethal. Together, our findings establish that FDX1 directly engages with LIAS, promoting its role in cellular protein lipoylation, a process essential in maintaining cell viability under low glucose conditions.

Solar-powered P450 catalysis: Engineering electron transfer pathways from photosynthesis to P450s

With the increasing focus on green chemistry, biocatalysis is becoming more widely used in the pharmaceutical and other chemical industries for sustainable production of high value and structurally complex chemicals. Cytochrome P450 monooxygenases (P450s) are attractive biocatalysts for industrial application due to their ability to transform a huge range of substrates in a stereo- and regiospecific manner. However, despite their appeal, the industrial application of P450s is limited by their dependence on costly reduced nicotinamide adenine dinucleotide phosphate (NADPH) and one or more auxiliary redox partner proteins. Coupling P450s to the photosynthetic machinery of a plant allows photosynthetically-generated electrons to be used to drive catalysis, overcoming this cofactor dependency. Thus, photosynthetic organisms could serve as photobioreactors with the capability to produce value-added chemicals using only light, water, CO2 and an appropriate chemical as substrate for the reaction/s of choice, yielding new opportunities for producing commodity and high-value chemicals in a carbon-negative and sustainable manner. This review will discuss recent progress in using photosynthesis for light-driven P450 biocatalysis and explore the potential for further development of such systems.

A Novel Oncogenic Role of FDX1 in Human Melanoma Related to PD-L1 Immune Checkpoint

The aim of this study was to evaluate the association between Ferredoxin 1 (FDX1) expression and the prognostic survival of tumor patients and predict the efficacy of immunotherapy response to antitumor drug sensitivity. FDX1 plays an oncogenic role in thirty-three types of tumors, based on TCGA and GEO databases, and further experimental validation in vitro was provided through multiple cell lines. FDX1 was expressed highly in multiple types of cancer and differently linked to the survival prognosis of tumorous patients. A high phosphorylation level was correlated with the FDX1 site of S177 in lung cancer. FDX1 exhibited a significant association with infiltrated cancer-associated fibroblasts and CD8⁺ T cells. Moreover, FDX1 demonstrated correlations with immune and molecular subtypes, as well as functional enrichments in GO/KEGG pathways. Additionally, FDX1 displayed relationships with the tumor mutational burden (TMB), microsatellite instability (MSI), DNA methylation, and RNA and DNA synthesis (RNAss/DNAss) within the tumor microenvironment. Notably, FDX1 exhibited a strong connection with immune checkpoint genes in the co-expression network. The validity of these findings was further confirmed through Western blotting, RT-qPCR, and flow cytometry experiments conducted on WM115 and A375 tumor cells. Elevated FDX1 expression has been linked to the enhanced effectiveness of PD-L1 blockade immunotherapy in melanoma, as observed in the GSE22155 and GSE172320 cohorts. Autodocking simulations have suggested that FDX1 may influence drug resistance by affecting the binding sites of antitumor drugs. Collectively, these findings propose that FDX1 could serve as a novel and valuable biomarker and represent an immunotherapeutic target for augmenting immune responses in various human cancers when used in combination with immune checkpoint inhibitors.

Molecular analysis of 12 Chinese patients with 11β-hydroxylase deficiency and in vitro functional study of 20 CYP11B1 missense variants

Steroid 11β-hydroxylase deficiency (11β-OHD) is a rare autosomal recessive disorder caused by pathogenic variants of CYP11B1 gene. This study aimed to perform molecular analysis of a Chinese 11β-OHD series and in vitro functional study of twenty CYP11B1 missense variants. Twelve Chinese patients with clinical diagnosis of 11β-OHD were included in the study to analyze their molecular etiology. Genomic DNA of patients was extracted to be sequenced all coding exons and intronic flanking sequences of CYP11B1. Fourteen missense variants found in 12 patients mentioned above along with 6 missense variants previously reported by our team were evaluated functionally. Amino acid substitutions were analyzed with computational program to determine their effects on the three-dimensional structure of CYP11B1 protein. Clinical characteristics and hormone levels at baseline of the 18 patients carrying 18 missense variants aforementioned were recorded to perform genotype-phenotype correlation. A total of 21 rare variants including 9 novel and 12 recurrent ones were identified in 12 patients, out of which 17 were missense, 2 were nonsense, 1 was a splice site variant, and 1 was a deletion-insertion variant. Results of in vitro functional study revealed that 3 out of 20 missense mutants (p.Leu3Pro, p.Gly267Ser, and p.Ala367Ser) had partial enzyme activity and the other 17 had little enzymatic activity. The impairment degree of enzymatic activity in vitro functional study was also reflected in the severity degree of interaction change between the wild-type/mutant-type amino acid and its adjacent amino acids in three-dimensional model. In conclusion, the addition of 9 novel variants expands the spectrum of CYP11B1 pathogenic variants. Our results demonstrate that twenty CYP11B1 variants lead to impaired 11β-hydroxylase activity in vitro. Visualizing these variants in the three-dimensional model structure of CYP11B1 protein can provide a plausible explanation for the results measured in vitro.

FDX1 regulates cellular protein lipoylation through direct binding to LIAS

Ferredoxins are a family of iron-sulfur (Fe-S) cluster proteins that serve as essential electron donors in numerous cellular processes that are conserved through evolution. The promiscuous nature of ferredoxins as electron donors enables them to participate in many metabolic processes including steroid, heme, vitamin D and Fe-S cluster biosynthesis in different organisms. However, the unique natural function(s) of each of the two human ferredoxins (FDX1 and FDX2) are still poorly characterized. We recently reported that FDX1 is both a crucial regulator of copper ionophore induced cell death and serves as an upstream regulator of cellular protein lipoylation, a mitochondrial lipid-based post translational modification naturally occurring on four mitochondrial enzymes that are crucial for TCA cycle function. Here we show that FDX1 regulates protein lipoylation by directly binding to the lipoyl synthase (LIAS) enzyme and not through indirect regulation of cellular Fe-S cluster biosynthesis. Metabolite profiling revealed that the predominant cellular metabolic outcome of FDX1 loss-of-function is manifested through the regulation of the four lipoylation-dependent enzymes ultimately resulting in loss of cellular respiration and sensitivity to mild glucose starvation. Transcriptional profiling of cells growing in either normal or low glucose conditions established that FDX1 loss-of-function results in the induction of both compensatory metabolism related genes and the integrated stress response, consistent with our findings that FDX1 loss-of-functions is conditionally lethal. Together, our findings establish that FDX1 directly engages with LIAS, promoting cellular protein lipoylation, a process essential in maintaining cell viability under low glucose conditions.

A Novel Cuprotosis-Related Gene FDX1 Signature for Overall Survival Prediction in Clear Cell Renal Cell Carcinoma Patients

Background

Ferredoxin 1 (FDX1) is a newly discovered gene regulating cuprotosis. However, the effect of FDX1 expression on clear renal cell carcinoma (ccRCC) is unknown.

Methods

Gene expression profiles and clinical data of ccRCC patients were downloaded from the Cancer Genome Atlas (TCGA) database. The differences in FDX1 expression between ccRCC and nonneoplastic tissues adjacent to cancer were analyzed by R software. The results were validated by GEO data, quantitative real-time polymerase chain reaction (qRT-PCR), western blotting (WB), and immunohistochemistry (IHC). Chi-square test was used to analyze the clinical pathological parameters. Kaplan-Meier survival analysis and Cox proportional hazard regression model selection were used to evaluate the effect of FDX1 expression on overall survival. Protein interaction networks were used to analyze other proteins that interact with FDX1. Signal pathway analysis was performed for possible FDX1 enrichment using GSEA and ssGSEA algorithms. Pan-cancer analysis of FDX1 was carried out through TCGA database.

Results

The FDX1 expression in nontumor tissues was significantly higher than that in ccRCC, and the expression difference was verified by GEO data, qRT-PCR, WB, and IHC. The high expression of FDX1 was significantly related to the well overall survival rate (P < 0.05). The chi-square test showed that the high expression of FDX1 was related to gender, TNM stage, T stage, lymph node metastasis, and pathological grade. Additionally, the FDX1 expression level was different in groups classified based on pathological grade, gender, TNM stage, T stage, lymph node metastasis, and distant metastasis (P < 0.05). The multivariate analysis revealed the high expression of FDX1 as an important independent predictor for overall survival. STRING database results showed that LIAS and LIPT1 may interact with FDX1 in the PPI network, which are also involved in the regulation of cuprotosis. The GSEA and ssGSEA results showed that the FDX1 was enriched in the anticancer pathway. The FDX1 high expression is associated with better prognosis in many cancers, as revealed by pan-cancer analysis.

Conclusion

FDX1 may play a role in the progression of ccRCC as a tumor suppressor gene. It can be used as a potential prognostic indicator and therapeutic target of ccRCC. However, the cuprotosis regulatory role in the development of ccRCC needs to be further verified.

Light-driven progesterone production by InP-(M. neoaurum) biohybrid system

Progesterone is one of the classical hormone drugs used in medicine for maintaining pregnancy. However, its manufacturing process, coupled with organic reagents and poisonous catalysts, causes irreversible environmental pollution. Recent advances in synthetic biology have demonstrated that the microbial biosynthesis of natural products, especially difficult-to-synthesize compounds, from building blocks is a promising strategy. Herein, overcoming the heterologous cytochrome P450 enzyme interdependency in Mycolicibacterium neoaurum successfully constructed the CYP11A1 running module to realize metabolic conversion from waste phytosterols to progesterone. Subsequently, progesterone yield was improved through strategies involving electron transfer and NADPH regeneration. Mutant CYP11A1 (mCYP11A1) and adrenodoxin reductase (ADR) were connected by a flexible linker (L) to form the chimera mCYP11A1-L-ADR to enhance electron transfer. The chimera mCYP11A1-L-ADR, adrenodoxin (ADX), and ADR-related homolog ARH1 were expressed in M. neoaurum, showed positive activity and produced 45 mg/L progesterone. This electron transfer strategy increased progesterone production by 3.95-fold compared with M. neoaurum expressing mCYP11A1, ADR, and ADX. Significantly, a novel inorganic-biological hybrid system was assembled by combining engineered M. neoaurum and InP nanoparticles to regenerate NADPH, which was increased 84-fold from the initial progesterone titer to 235 ± 50 mg/L. In summary, this work highlights the green and sustainable potential of obtaining synthetic progesterone from sterols in M. neoaurum.

Three pairs of surrogate redox partners comparison for Class I cytochrome P450 enzyme activity reconstitution

Most P450s require redox partners for the electron transfer during catalysis. However, little information is available on cognate redox partners for P450s, which greatly limits P450 function exploration and practical application. Thus, the stategy of building various hybrid P450 catalytic systems with surrogate redox partner has often adopted to engineer P450 biocatalysts. In this study, we compare three pairs of frequently-used surrogate redox partner SelFdx1499/SelFdR0978, Adx/AdR and Pdx/PdR and in terms of their electron transfer properties. The three selected bacterial Class I P450s include PikC, P450sca-2 and CYP-sb21, which are responsible for production of high-value-added products. Here we show that SelFdx1499/SelFdR0978 is the most promising redox partner compared to Adx/AdR and Pdx/PdR. The results provide insights into the domination for P450-redox partner interactions in modulating the catalytic activity of P450s. This study not only produces a more active biocatalyst but also suggests a general chose for a universal reductase which would facilitate engineering of P450 catalyst.

Aiming for an efficient Class I cytochrome P450 catalytic system, three pairs of surrogate redox partners for biocatalyst applications are tested.

Congenital adrenal hyperplasia caused by compound heterozygosity of two novel CYP11B1 gene variants

BACKGROUND

Congenital adrenal hyperplasia (CAH) is an autosomal recessive disorder caused by pathogenic variants in seven genes involved in the cortisol and aldosterone biosynthetic pathway. The second most common cause, 11β-hydroxylase deficiency (11βOHD), is attributed to pathogenic variants in the CYP11B1 gene encoding for the enzyme 11β-hydroxylase (11βOH).

CASE PRESENTATION

A 13-year-old girl was referred to the pediatric endocrinologist due to a syncopal episode. She is the third child of non-consanguineous parents. She presented with premature adrenarche at the age of 6 years and menarche at the age of 12 years. On physical examination, her height was 154.5 cm and weight 50 kg, while she presented with acne, hirsutism, clitoromegaly, and normal blood pressure. Laboratory investigation revealed increased androgen levels and poor cortisol response to the ACTH stimulation test. From the family history, the mother was diagnosed with CAH at the age of 10 years and was under treatment with methylprednisolone. Previous molecular investigation of the CYP21A2 gene was negative. Due to the increased androstenedione levels in the index patient, the suspicion of 11βOH was raised, and she was investigated for 11-deoxycortisol, 11-deoxycorticosterone, and CYP11B1 gene pathogenic variants. The patient and her mother were found to be compound heterozygous for two novel variants of the CYP11B1 gene.

CONCLUSION

We present a case of CAH due to compound heterozygosity of two novel pathogenic variants of the CYP11B1 gene, emphasizing the importance of molecular investigation in order to confirm clinical diagnosis and allow proper genetic counseling of the family.

Involvement of CYP2 and mitochondrial clan P450s of Helicoverpa armigera in xenobiotic metabolism

Insect CYP2 and mitochondrial clan P450s are relatively conserved genes encoding enzymes generally thought to be involved in biosynthesis or metabolism of endobiotics. However, emerging evidence argues they have potential roles in chemical defense as well, but their actual detoxification functions remain largely unknown. Here, we focused on the full complement of 8 CYP2 and 10 mitochondrial P450s in the generalist herbivore, Helicoverpa armigera. Their varied spatiotemporal expression profiles were analyzed and reflected their specific functions. For functional study of the mitochondrial clan P450s, the redox partners, adrenodoxin reductase (AdR) and adrenodoxin (Adx), were identified from genomes of eight insects and an efficient in vitro electron transfer system of mitochondrial P450 was established by co-expression with Adx and AdR of H. armigera. All CYP2 clan P450s and 8 mitochondrial P450s were successfully expressed in Sf9 cells and compared functionally. In vitro metabolism assays showed that two CYP2 clan P450s (CYP305B1 and CYP18A1) and CYP333B3 (mito clan) could epoxidize aldrin to dieldrin, while CYP305B1 and CYP339A1 (mito clan) have limited but significant hydroxylation capacities to esfenvalerate. CYP303A1 of the CYP2 clan exhibits high metabolic efficiency to 2-tridecanone. Screening the xenobiotic metabolism competence of CYP2 and mitochondrial clan P450s not only provides new insights on insect chemical defense but also can give indications on their physiological functions in H. armigera and other insects.

Electrochemical characterization of mutant forms of rubredoxin B from Mycobacterium tuberculosis

Electron transfer in metalloproteins is a driving force for many biological processes and widely distributed in nature. Rubredoxin B (RubB) from Mycobacterium tuberculosis is a first example among [1Fe-0S] proteins that support catalytic activity of terminal sterol-monooxygenases enabling its application in metabolic engineering. To explore the tolerance of RubB to the specific amino acid changes we evaluated the effect of surface mutations on its electrochemical properties. Based on the RubB fold we also designed the mutant with a putative additional site for protein-protein interactions to further evaluate electron transfer and electrochemical properties. The investigation of redox properties of mutant variants of RubB was done using screen-printed graphite electrodes (SPEs) modified with stable dispersion of multi-walled carbon nanotubes (MWCNTs). The redox potentials (midpoint potentials, E^0Ꞌ) of mutants did not significantly differ from the wild type protein and vary in the range of -264 to -231 mV vs. Ag/AgCl electrode. However, all mutations affect electron transfer rate between the protein and electrode. Notably, the modulation of the protein-protein interactions was observed for the insertion mutant suggesting the possibility of tailoring of rubredoxin for the selected redox-partner. Overall, RubB is tolerant to the significant modifications in its structure enabling rational engineering of novel redox proteins.

The role of FDX1 in granulosa cell of Polycystic ovary syndrome (PCOS)

BACKGROUND

To explore the development mechanism of PCOS and Transcriptomics was applied to seek the key gene.

METHODS

Transcriptomics marked by UID (unique identifier) technique of granulosa cell in PCOS and control women was carried out and key gene was picked up. Then the key gene in granulosa cell was measured by RT-PCR. Two PCOS models modeling with Letrozole and Testosterone Propionate were implemented and the key gene in granulosa cell of ovary was measured by immunohistochemistry to verify the relation with PCOS.

RESULTS

GO-enrich of transcriptomics concentrated in domain steroid metabolism and domain mitochondria. Different genes were sought from coexisting in both domain steroid metabolism and domain mitochondria. Finally, five different genes including CYP11A1、CYB5R1、STAR、FDX1 and AMACR were obtained. RT-PCR was implemented to furtherly verify the downregulating mRNA of FDX1 in PCOS, which showed the consistent outcome with the transcriptomics. Level of FDX1 protein in granulosa cell of antral follicle in two PCOS models was measured and decreased.

CONCLUSIONS

FDX1 was related with steroid metabolism and mitochondrial and may participate in the development of PCOS.

Resurrection and characterization of ancestral CYP11A1 enzymes

Mitochondrial cytochromes P450 presumably originated from a common microsomal P450 ancestor. However, it is still unknown how ancient mitochondrial P450s were able to retain their oxygenase function following relocation to the mitochondrial matrix and later emerged as enzymes specialized for steroid hormone biosynthesis in vertebrates. Here, we used the approach of ancestral sequence reconstruction (ASR) to resurrect ancient CYP11A1 enzymes and characterize their unique biochemical properties. Two ancestral CYP11A1 variants, CYP11A_Mammal_N101 and CYP11A_N1, as well as an extant bovine form were recombinantly expressed and purified to homogeneity. All enzymes showed characteristic P450 spectral properties and were able to convert cholesterol as well as other sterol substrates to pregnenolone, yet with different specificities. The vertebrate CYP11A_N1 ancestor preferred the cholesterol precursor, desmosterol, as substrate suggesting a convergent evolution of early cholesterol metabolism and CYP11A1 enzymes. Both ancestors were able to withstand increased levels of hydrogen peroxide but only the ancestor CYP11A_N1 showed increased thermostability (~ 25 °C increase in T₅₀ ) compared with the extant CYP11A1. The extraordinary robustness of ancient mitochondrial P450s, as demonstrated for CYP11A_N1, may have allowed them to stay active when presented with poorly compatible electron transfer proteins and resulting harmful ROS in the new environment of the mitochondrial matrix. To the best of our knowledge, this work represents the first study that describes the resurrection of ancient mitochondrial P450 enzymes. The results will help to understand and gain fundamental functional insights into the evolutionary origins of steroid hormone biosynthesis in animals.

Solution structure for an Encephalitozoon cuniculi adrenodoxin-like protein in the oxidized state

Encephalitozoon cuniculi is a unicellular, obligate intracellular eukaryotic parasite in the Microsporidia family and one of the agents responsible for microsporidosis infections in humans. Like most Microsporidia, the genome of E. cuniculi is markedly reduced and the organism contains mitochondria-like organelles called mitosomes instead of mitochondria. Here we report the solution NMR structure for a protein physically associated with mitosome-like organelles in E. cuniculi, the 128-residue, adrenodoxin-like protein Ec-Adx (UniProt ID Q8SV19) in the [2Fe-2S] ferredoxin superfamily. Oxidized Ec-Adx contains a mixed four-strand β-sheet, β2-β1-β4-β3 (↓↑↑↓), loosely encircled by three α-helices and two 3₁₀ -helices. This fold is similar to the structure observed in other adrenodoxin and adrenodoxin-like proteins except for the absence of a fifth anti-parallel β-strand next to β3 and the position of α3. Cross peaks are missing or cannot be unambiguously assigned for 20 amide resonances in the ¹ H-¹⁵ N HSQC spectrum of Ec-Adx. These missing residues are clustered primarily in two regions, G48-V61 and L94-L98, containing the four cysteine residues predicted to ligate the paramagnetic [2Fe-2S] cluster. Missing amide resonances in ¹ H-¹⁵ N HSQC spectra are detrimental to NMR-based solution structure calculations because ¹ H-¹ H NOE restraints are absent (glass half-empty) and this may account for the absent β-strand (β5) and the position of α3 in oxidized Ec-Adx. On the other hand, the missing amide resonances unambiguously identify the presence, and immediate environment, of the paramagnetic [2Fe-2S] cluster in oxidized Ec-Adx (glass half-full).

The hunt for radiation biomarkers: current situation

Purpose: The possibility of a large-scale acute radiation exposure necessitates the development of new methods that could provide a rapid assessment of the doses received by individuals using high-throughput technologies. There is also a great interest in developing new biomarkers of dose exposure, which could be used in large molecular epidemiological studies in order to correlate estimated doses received and health effects. The goal of this review was to summarize current literature focused on biological dosimetry, namely radiation-responsive biomarkers.Methods: The studies involved in this review were thoroughly selected according to the determined criteria and PRISMA guidelines.Results: We described briefly recent advances in radiation genomics and metabolomics, giving particular emphasis to proteomic analysis. The majority of studies were performed on animal models (rats, mice, and non-human primates). They have provided much beneficial information, but the most relevant tests have been done on human (oncological) patients. By inspecting the radiaiton biodosimetry literate of the last 10 years, we identified a panel of candidate markers for each -omic approach involved.Conslusions: We reviewed different methodological approaches and various biological materials, which can be exploited for dose-effect prediction. The protein biomarkers from human plasma are ideal for this specific purpose. From a plethora of candidate markers, FDXR is a very promising transcriptomic candidate, and importantly this biomarker was also confirmed by some studies at protein level in humans.

SPR-Based study of affinity of cytochrome P450s / redox partners interactions modulated by steroidal substrates

The goal of this work was to test the hypothesis that the affinity of protein-protein interactions in the cytochrome P450-dependent monooxygenase system is modulated by the low-molecular-weight compounds (substrates or inhibitors). The surface plasmon resonance (SPR) based study was carried out using the recombinant protein preparations of three microsomal cytochromes P450 (CYP17A1, CYP21A2, and CYP2C19) and their redox partners: cytochrome b5 (CYB5A), NADPH - cytochrome P450 reductase (CPR), and also iron-sulfur protein adrenodoxin (Adx). As a result, we have revealed some specificity of the influence of the steroid substrates on the binding affinity of CYPs with their redox partners, namely: the lack of effect on CPR/CYPs and Adx/CYP complex formation, and a significant effect on interactions between CYB5A and steroidogenic CYPs. The equilibrium dissociation constant (Kd) value of the CYB5A/CYP17A1 complex decreased by 5 times in the presence of progesterone (P4), which was due to a 10 times increase in the association rate constant (k_on). In this case, a twofold increase in the dissociation rate constant (k_off) value of CYB5A/CYP17A1 complex formation was observed. It was also demonstrated that the affinity of CYB5A/CYP17A1 interaction increased in the presence of two other steroidal substrates 17α-hydroxyprogesterone and pregnenolone and that effect was comparable with P4. In contrast, only the twofold decrease in the affinity of CYB5A/CYP21A2 interaction in the presence of P4 was caused by a slight increase in the k_off value (the k_on value of the complex did not change). This indicates a different format of the steroidal substrates effects expressed in a change in the stability of the CYB5A/CYPs complexes. Thus, it was found that P4 modulated the both kinetic and equilibrium constants of CYB5A/CYP17A1 and CYB5/CYP21A2 complex formation and complexes, while not affecting the CYB5A/CYP2C19 interaction (2C19 is the cytochrome P450 isoenzyme possessing broad substrate specificity), thereby indicating a specific influence of steroidal substrates on interactions involving steroidogenic CYPs. Our results are consistent with current understanding of the role of CYB5A as a regulator of cytochrome P450 activity in P450-dependent monooxygenase system.

Respiratory Membrane Protein Complexes Convert Chemical Energy

The invention of a biological membrane which is used as energy storage system to drive the metabolism of a primordial, unicellular organism represents a key event in the evolution of life. The innovative, underlying principle of this key event is respiration. In respiration, a lipid bilayer with insulating properties is chosen as the site for catalysis of an exergonic redox reaction converting substrates offered from the environment, using the liberated Gibbs free energy (ΔG) for the build-up of an electrochemical H⁺ (proton motive force, PMF) or Na⁺ gradient (sodium motive force, SMF) across the lipid bilayer. Very frequently , several redox reactions are performed in a consecutive manner, with the first reaction delivering a product which is used as substrate for the second redox reaction, resulting in a respiratory chain. From today's perspective, the (mostly) unicellular bacteria and archaea seem to be much simpler and less evolved when compared to multicellular eukaryotes. However, they are overwhelmingly complex with regard to the various respiratory chains which permit survival in very different habitats of our planet, utilizing a plethora of substances to drive metabolism. This includes nitrogen, sulfur and carbon compounds which are oxidized or reduced by specialized, respiratory enzymes of bacteria and archaea which lie at the heart of the geochemical N, S and C-cycles. This chapter gives an overview of general principles of microbial respiration considering thermodynamic aspects, chemical reactions and kinetic restraints. The respiratory chains of Escherichia coli and Vibrio cholerae are discussed as models for PMF- versus SMF-generating processes, respectively. We introduce main redox cofactors of microbial respiratory enzymes, and the concept of intra-and interelectron transfer. Since oxygen is an electron acceptor used by many respiratory chains, the formation and removal of toxic oxygen radicals is described. Promising directions of future research are respiratory enzymes as novel bacterial targets, and biotechnological applications relying on respiratory complexes.

Mechanisms of Mitochondrial Redox Signaling in Psychosocial Stress-Responsive Systems: New Insights into an Old Story

SIGNIFICANCE

Psychosocial stress is associated with alterations in serum glucocorticoids and cytokines, such as interleukin-6 (IL-6) and IL-1β, which functionally interact. However, the molecular mechanisms and physiological relationship between the two systems within the context of stress exposure are not well characterized. Recent Advances: Extracellular IL-6, which stimulates the release of cortisol from the zona fasciculata of the adrenal cortex, mediates its intracellular effects by tyrosine phosphorylation of the transcription factor signal transducer and activator of transcription 3 (STAT3). Mitochondrial electron transfer reactions are involved in both STAT3-driven ATP production in oxidative respiration and adrenocortical steroid biosynthesis.

CRITICAL ISSUES

The role of STAT3 in oxidative respiration and steroidogenesis suggests that it integrates both nuclear and mitochondrial actions, thereby preserving main steps of glucocorticoid biosynthesis in the adrenal gland under psychosocial stress. This review discusses the notion that these two pathways are together simultaneously involved in protection against chronic stressors.

FUTURE DIRECTIONS

Linking the function of cytokines and main components of the hypothalamic-pituitary-adrenal (HPA) axis to molecular mechanisms of mitochondrial redox signaling will be essential for a better understanding of the relevant stress-responsive systems engaged in stress vulnerability. Antioxid. Redox Signal. 28, 760-772.

Mapping cellular Fe-S cluster uptake and exchange reactions - divergent pathways for iron-sulfur cluster delivery to human ferredoxins

Ferredoxins are protein mediators of biological electron-transfer reactions and typically contain either [2Fe-2S] or [4Fe-4S] clusters. Two ferredoxin homologues have been identified in the human genome, Fdx1 and Fdx2, that share 43% identity and 69% similarity in protein sequence and both bind [2Fe-2S] clusters. Despite the high similarity, the two ferredoxins play very specific roles in distinct physiological pathways and cannot replace each other in function. Both eukaryotic and prokaryotic ferredoxins and homologues have been reported to receive their Fe-S cluster from scaffold/delivery proteins such as IscU, Isa, glutaredoxins, and Nfu. However, the preferred and physiologically relevant pathway for receiving the [2Fe-2S] cluster by ferredoxins is subject to speculation and is not clearly identified. In this work, we report on in vitro UV-visible (UV-vis) circular dichroism studies of [2Fe-2S] cluster transfer to the ferredoxins from a variety of partners. The results reveal rapid and quantitative transfer to both ferredoxins from several donor proteins (IscU, Isa1, Grx2, and Grx3). Transfer from Isa1 to Fdx2 was also observed to be faster than that of IscU to Fdx2, suggesting that Fdx2 could receive its cluster from Isa1 instead of IscU. Several other transfer combinations were also investigated and the results suggest a complex, but kinetically detailed map for cellular cluster trafficking. This is the first step toward building a network map for all of the possible iron-sulfur cluster transfer pathways in the mitochondria and cytosol, providing insights on the most likely cellular pathways and possible redundancies in these pathways.

Efficient synthesis of phycocyanobilin in mammalian cells for optogenetic control of cell signaling

Optogenetics is a powerful tool to precisely manipulate cell signaling in space and time. For example, protein activity can be regulated by several light-induced dimerization (LID) systems. Among them, the phytochrome B (PhyB)-phytochrome-interacting factor (PIF) system is the only available LID system controlled by red and far-red lights. However, the PhyB-PIF system requires phycocyanobilin (PCB) or phytochromobilin as a chromophore, which must be artificially added to mammalian cells. Here, we report an expression vector that coexpresses HO1 and PcyA with Ferredoxin and Ferredoxin-NADP+ reductase for the efficient synthesis of PCB in the mitochondria of mammalian cells. An even higher intracellular PCB concentration was achieved by the depletion of biliverdin reductase A, which degrades PCB. The PCB synthesis and PhyB-PIF systems allowed us to optogenetically regulate intracellular signaling without any external supply of chromophores. Thus, we have provided a practical method for developing a fully genetically encoded PhyB-PIF system, which paves the way for its application to a living animal.

Human Mitochondrial Ferredoxin 1 (FDX1) and Ferredoxin 2 (FDX2) Both Bind Cysteine Desulfurase and Donate Electrons for Iron-Sulfur Cluster Biosynthesis

Ferredoxins play an important role as an electron donor in iron-sulfur (Fe-S) cluster biosynthesis. Two ferredoxins, human mitochondrial ferredoxin 1 (FDX1) and human mitochondrial ferredoxin 2 (FDX2), are present in the matrix of human mitochondria. Conflicting results have been reported regarding their respective function in mitochondrial iron-sulfur cluster biogenesis. We report here biophysical studies of the interaction of these two ferredoxins with other proteins involved in mitochondrial iron-sulfur cluster assembly. Results from nuclear magnetic resonance spectroscopy show that both FDX1 and FDX2 (in both their reduced and oxidized states) interact with the protein complex responsible for cluster assembly, which contains cysteine desulfurase (NFS1), ISD11 (also known as LYRM4), and acyl carrier protein (Acp). In all cases, ferredoxin residues close to the Fe-S cluster are involved in the interaction with this complex. Isothermal titration calorimetry results showed that FDX2 binds more tightly to the cysteine desulfurase complex than FDX1 does. The reduced form of each ferredoxin became oxidized in the presence of the cysteine desulfurase complex when l-cysteine was added, leading to its conversion to l-alanine and the generation of sulfide. In an in vitro reaction, the reduced form of each ferredoxin was found to support Fe-S cluster assembly on ISCU; the rate of cluster assembly was faster with FDX2 than with FDX1. Taken together, these results show that both FDX1 and FDX2 can function in Fe-S cluster assembly in vitro.

The selective oxidation of substituted aromatic hydrocarbons and the observation of uncoupling via redox cycling during naphthalene oxidation by the CYP101B1 system

Oxidation of polyaromatic hydrocarbons by P450s can be lowered by redox cycling but CYP101B1 regioselectively hydroxylated substituted naphthalenes and biphenyls.

A Fluorescent Readout for the Oxidation State of Electron Transporting Proteins in Cell Free Settings

Pathways involving sequential electron transfer between multiple proteins are ubiquitous in nature. Here, we demonstrate a new class of fluorescent protein-based reporters for monitoring electron transport through such multistage cascades, specifically those involving ferredoxin-like electron transporters. We created protein fusions between mammalian Adrenodoxin (Adx) and plant Ferredoxin (Fdx) with fluorescent proteins of different colors and found that the fluorescence of such fusions is highly sensitive to the redox state of the electron transporter. The increase in fluorescence from the oxidized to the reduced state was inversely proportional to the linker length between the fusion partners. We first used our approach to quantitatively characterize electron transfer from NADPH through Adrenodoxin Reductase (AdR) to Adrenodoxin (Adx). Our data allowed us to build a detailed mathematical model of this mitochondrial electron transfer chain and validate previously proposed mechanisms. Then, we showed that an Adx-GFP fusion could serve as a sensor for the activity of bacterial Type I Cytochrome P450s (CYPs), a very large class of enzymes with important roles in biotechnology. We further showed that fluorescence of a direct fusion between CYP and GFP was sensitive to CYP activity, suggesting that our approach is applicable to an even broader class of proteins, which undergo a redox state change during their work cycle.

Ferredoxin 1b (Fdx1b) Is the Essential Mitochondrial Redox Partner for Cortisol Biosynthesis in Zebrafish

Mitochondrial cytochrome P450 (CYP) enzymes rely on electron transfer from the redox partner ferredoxin 1 (FDX1) for catalytic activity. Key steps in steroidogenesis require mitochondrial CYP enzymes and FDX1. Over 30 ferredoxin mutations have been explored in vitro; however, no spontaneously occurring mutations have been identified in humans leaving the impact of FDX1 on steroidogenesis in the whole organism largely unknown. Zebrafish are an important model to study human steroidogenesis, because they have similar steroid products and endocrine tissues. This study aimed to characterize the influence of ferredoxin on steroidogenic capacity in vivo by using zebrafish. Zebrafish have duplicate ferredoxin paralogs: fdx1 and fdx1b. Although fdx1 was observed throughout development and in most tissues, fdx1b was expressed after development of the zebrafish interrenal gland (counterpart to the mammalian adrenal gland). Additionally, fdx1b was restricted to adult steroidogenic tissues, such as the interrenal, gonads, and brain, suggesting that fdx1b was interacting with steroidogenic CYP enzymes. By using transcription activator-like effector nucleases, we generated fdx1b mutant zebrafish lines. Larvae with genetic disruption of fdx1b were morphologically inconspicuous. However, steroid hormone analysis by liquid chromatography tandem mass spectrometry revealed fdx1b mutants failed to synthesize glucocorticoids. Additionally, these mutants had an up-regulation of the hypothalamus-pituitary-interrenal axis and showed altered dark-light adaptation, suggesting impaired cortisol signaling. Antisense morpholino knockdown confirmed Fdx1b is required for de novo cortisol biosynthesis. In summary, by using zebrafish, we generated a ferredoxin knockout model system, which demonstrates for the first time the impact of mitochondrial redox regulation on glucocorticoid biosynthesis in vivo.

A Conformational Switch Triggers Nitrogenase Protection from Oxygen Damage by Shethna Protein II (FeSII)

The two-component metalloprotein nitrogenase catalyzes the reductive fixation of atmospheric dinitrogen into bioavailable ammonium in diazotrophic prokaryotes. The process requires an efficient energy metabolism, so that although the metal clusters of nitrogenase rapidly decompose in the presence of dioxygen, many free-living diazotrophs are obligate aerobes. In order to retain the functionality of the nitrogen-fixing enzyme, some of these are able to rapidly "switch-off" nitrogenase, by shifting the enzyme into an inactive but oxygen-tolerant state. Under these conditions the two components of nitrogenase form a stable, ternary complex with a small [2Fe:2S] ferredoxin termed FeSII or the "Shethna protein II". Here we have produced and isolated Azotobacter vinelandii FeS II and have determined its three-dimensional structure to 2.1 Å resolution by X-ray diffraction. In the crystals, the dimeric protein was present in two distinct states that differ in the conformation of an extended loop in close proximity to the iron-sulfur cluster. We show that this rearrangement is redox-dependent and forms the molecular basis for oxygen-dependent conformational protection of nitrogenase. Protection assays highlight that FeSII binds to a preformed complex of MoFe and Fe protein upon activation, primarily through electrostatic interactions. The surface properties and known complexes of nitrogenase component proteins allow us to propose a model of the conformationally protected ternary complex of nitrogenase.

Highly Efficient CYP167A1 (EpoK) dependent Epothilone B Formation and Production of 7-Ketone Epothilone D as a New Epothilone Derivative

Since their discovery in the soil bacterium Sorangium cellulosum, epothilones have emerged as a valuable substance class with promising anti-tumor activity. Because of their benefits in the treatment of cancer and neurodegenerative diseases, epothilones are targets for drug design and pharmaceutical research. The final step of their biosynthesis – a cytochrome P450 mediated epoxidation of epothilone C/D to A/B by CYP167A1 (EpoK) – needs significant improvement, in particular regarding the efficiency of its redox partners. Therefore, we have investigated the ability of various hetero- and homologous redox partners to transfer electrons to EpoK. Hereby, a new hybrid system was established with conversion rates eleven times higher and V_max of more than seven orders of magnitudes higher as compared with the previously described spinach redox chain. This hybrid system is the most efficient redox chain for EpoK described to date. Furthermore, P450s from So ce56 were identified which are able to convert epothilone D to 14-OH, 21-OH, 26-OH epothilone D and 7-ketone epothilone D. The latter one represents a novel epothilone derivative and is a suitable candidate for pharmacological tests. The results revealed myxobacterial P450s from S. cellulosum So ce56 as promising candidates for protein engineering for biotechnological production of epothilone derivatives.

Functionalized PHB granules provide the basis for the efficient side-chain cleavage of cholesterol and analogs in recombinant Bacillus megaterium

Background

Cholesterol, the precursor of all steroid hormones, is the most abundant steroid in vertebrates and exhibits highly hydrophobic properties, rendering it a difficult substrate for aqueous microbial biotransformations. In the present study, we developed a Bacillus megaterium based whole-cell system that allows the side-chain cleavage of this sterol and investigated the underlying physiological basis of the biocatalysis.

Results

CYP11A1, the side-chain cleaving cytochrome P450, was recombinantly expressed in the Gram-positive soil bacterium B. megaterium combined with the required electron transfer proteins. By applying a mixture of 2-hydroxypropyl-β-cyclodextrin and Quillaja saponin as solubilizing agents, the zoosterols cholesterol and 7-dehydrocholesterol, as well as the phytosterol β-sitosterol could be efficiently converted to pregnenolone or 7-dehydropregnenolone. Fluorescence-microscopic analysis revealed that cholesterol accumulates in the carbon and energy storage-serving poly(3-hydroxybutyrate) (PHB) bodies and that the membrane proteins CYP11A1 and its redox partner adrenodoxin reductase (AdR) are likewise localized to their surrounding phospholipid/protein monolayer. The capacity to store cholesterol was absent in a mutant strain devoid of the PHB-producing polymerase subunit PhaC, resulting in a drastically decreased cholesterol conversion rate, while no effect on the expression of the recombinant proteins could be observed.

Conclusion

We established a whole-cell system based on B. megaterium, which enables the conversion of the steroid hormone precursor cholesterol to pregnenolone in substantial quantities. We demonstrate that the microorganism’s PHB granules, aggregates of bioplastic coated with a protein/phospholipid monolayer, are crucial for the high conversion rate by serving as substrate storage. This microbial system opens the way for an industrial conversion of the abundantly available cholesterol to any type of steroid hormones, which represent one of the biggest groups of drugs for the treatment of a wide variety of diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s12934-015-0300-y) contains supplementary material, which is available to authorized users.

The CYP11B subfamily

The biosynthesis of steroid hormones is dependent on P450-catalyzed reactions. In mammals, cholesterol is the common precursor of all steroid hormones, and its conversion to pregnenolone is the initial and rate-limiting step in hormone biosynthesis in steroidogenic tissues such as gonads and adrenal glands. The production of glucocorticoids and mineralocorticoids takes place in the adrenal gland and the final steps are catalyzed by 2 mitochondrial cytochromes P450, CYP11B1 (11β-hydroxylase or P45011β) and CYP11B2 (aldosterone synthase or P450aldo). The occurrence and development of these 2 enzymes in different species, their contribution to the biosynthesis of steroid hormones as well as their regulation at different levels (gene expression, cellular regulation, regulation on the level of proteins) is the topic of this chapter.

Impact of a novel homozygous mutation in nicotinamide nucleotide transhydrogenase on mitochondrial DNA integrity in a case of familial glucocorticoid deficiency

BACKGROUND

Familial Glucocorticoid Deficiency (FGD) is a rare autosomal recessive disorder that is characterized by isolated glucocorticoid deficiency. Recently, mutations in the gene encoding for the mitochondrial nicotinamide nucleotide transhydrogenase (NNT) have been identified as a causative gene for FGD; however, no NNT activities have been reported in FGD patients carrying NNT mutations.

METHODS

Clinical, biochemical and molecular analyses of lymphocytes from FDG homozygous and heterozygous carriers for the F215S NNT mutation.

RESULTS

In this study, we described an FGD-affected Japanese patient carrying a novel NNT homozygous mutation (c.644T>C; F215S) with a significant loss-of-function (NNT activity = 31% of healthy controls) in peripheral blood cells' mitochondria. The NNT activities of the parents, heterozygous for the mutation, were 61% of controls.

CONCLUSIONS

Our results indicated that (i) mitochondrial biogenesis (citrate synthase activity) and/or mtDNA replication (mtDNA copy number) were affected at ≤60% NNT activity because these parameters were affected in individuals carrying either one or both mutated alleles; and (ii) other outcomes (mtDNA deletions, protein tyrosine nitration, OXPHOS capacity) were affected at ≤30% NNT activity as also observed in murine cerebellar mitochondria from C57BL/6J (NNT^-/-) vs. C57BL/6JN (NNT^+/+) substrains.

GENERAL SIGNIFICANCE

By studying a family affected with a novel point mutation in the NNT gene, a gene-dose response was found for various mitochondrial outcomes providing for novel insights into the role of NNT in the maintenance of mtDNA integrity beyond that described for preventing oxidative stress.

A recombinant CYP11B1 dependent Escherichia coli biocatalyst for selective cortisol production and optimization towards a preparative scale

BACKGROUND

Human mitochondrial CYP11B1 catalyzes a one-step regio- and stereoselective 11β-hydroxylation of 11-deoxycortisol yielding cortisol which constitutes not only the major human stress hormone but also represents a commercially relevant therapeutic drug due to its anti-inflammatory and immunosuppressive properties. Moreover, it is an important intermediate in the industrial production of synthetic pharmaceutical glucocorticoids. CYP11B1 thus offers a great potential for biotechnological application in large-scale synthesis of cortisol. Because of its nature as external monooxygenase, CYP11B1-dependent steroid hydroxylation requires reducing equivalents which are provided from NADPH via a redox chain, consisting of adrenodoxin reductase (AdR) and adrenodoxin (Adx).

RESULTS

We established an Escherichia coli based whole-cell system for selective cortisol production from 11-deoxycortisol by recombinant co-expression of the demanded 3 proteins. For the subsequent optimization of the whole-cell activity 3 different approaches were pursued: Firstly, CYP11B1 expression was enhanced 3.3-fold to 257 nmol∗L(-1) by site-directed mutagenesis of position 23 from glycine to arginine, which was accompanied by a 2.6-fold increase in cortisol yield. Secondly, the electron transfer chain was engineered in a quantitative manner by introducing additional copies of the Adx cDNA in order to enhance Adx expression on transcriptional level. In the presence of 2 and 3 copies the initial linear conversion rate was greatly accelerated and the final product concentration was improved 1.4-fold. Thirdly, we developed a screening system for directed evolution of CYP11B1 towards higher hydroxylation activity. A culture down-scale to microtiter plates was performed and a robot-assisted, fluorescence-based conversion assay was applied for the selection of more efficient mutants from a random library.

CONCLUSIONS

Under optimized conditions a maximum productivity of 0.84 g cortisol∗L(-1)∗d(-1) was achieved, which clearly shows the potential of the developed system for application in the pharmaceutical industry.

Ferredoxin, in conjunction with NADPH and ferredoxin-NADP reductase, transfers electrons to the IscS/IscU complex to promote iron-sulfur cluster assembly

Fe–S cluster biogenesis is an essential pathway coordinated by a network of protein–protein interactions whose functions include desulfurase activity, substrate delivery, electron transfer and product transfer. In an effort to understand the intricacies of the pathway, we have developed an in vitro assay to follow the ferredoxin role in electron transfer during Fe–S cluster assembly. Previously, assays have relied upon the non-physiological reducing agents dithionite and dithiothreitol to assess function. We have addressed this shortcoming by using electron transfer between NADPH and ferredoxin-NADP-reductase to reduce ferredoxin. Our results show that this trio of electron transfer partners are sufficient to sustain the reaction in in vitro studies, albeit with a rate slower compared with DTT-mediated cluster assembly. We also show that, despite overlapping with the CyaY protein in binding to IscS, Fdx does not interfere with the inhibitory activity of this protein. We suggest explanations for these observations which have important consequences for understanding the mechanism of cluster formation. Cofactor-dependent proteins: evolution, chemical diversity and bio-applications.

•

We have coupled ferredoxin (Fdx) function in Fe-S cluster biogenesis to electron transfer between NADPH via Fdx-NADP-reductase.

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Our results show that this trio of electron transfer partners is sufficient to sustain the reaction in vitro.

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Despite sharing the same binding site on IscS, Fdx does not interfere with the inhibitory activity of CyaY.

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These observations have important consequences for understanding the mechanism of cluster formation.

The crystal structure of the versatile cytochrome P450 enzyme CYP109B1 from Bacillus subtilis

The crystal structure of the versatile CYP109B1 enzyme from Bacillus subtilis has been solved at 1.8 Å resolution. This is the first structure of an enzyme from this CYP family, whose members are prevalent across diverse species of bacteria. In the crystal structure the enzyme has an open conformation with an access channel leading from the heme to the surface. The substrate-free structure reveals the location of the key residues in the active site that are responsible for binding the substrate in the correct orientation for regioselective oxidation. Importantly, there are significant differences among these residues in members of the CYP109 and closely related CYP106 families and these likely account for the variations in substrate binding and oxidation profiles observed with these enzymes. A whole-cell oxidation biosystem was developed, which contains CYP109B1 and a phthalate family oxygenase reductase (PFOR), from Pseudomonas putida KT24440, as the electron transfer partner. This electron transfer system is able to support CYP109B1 activity resulting in the regioselective hydroxylation of both α- and β-ionone in vivo and in vitro. The PFOR is therefore a versatile electron transfer partner that is able to support the activity of CYP enzymes from other bacterium. The crystal structure of CYP109B1 has a positively charged proximal face and this explains why it can interact with PFOR and adrenodoxin which are predominantly negatively charged around their [2Fe-2S] clusters.

Mechanistic basis of electron transfer to cytochromes p450 by natural redox partners and artificial donor constructs

Cytochromes P450 (P450s) are hemoproteins catalyzing oxidative biotransformation of a vast array of natural and xenobiotic compounds. Reducing equivalents required for dioxygen cleavage and substrate hydroxylation originate from different redox partners including diflavin reductases, flavodoxins, ferredoxins and phthalate dioxygenase reductase (PDR)-type proteins. Accordingly, circumstantial analysis of structural and physicochemical features governing donor-acceptor recognition and electron transfer poses an intriguing challenge. Thus, conformational flexibility reflected by togging between closed and open states of solvent exposed patches on the redox components was shown to be instrumental to steered electron transmission. Here, the membrane-interactive tails of the P450 enzymes and donor proteins were recognized to be crucial to proper orientation toward each other of surface sites on the redox modules steering functional coupling. Also, mobile electron shuttling may come into play. While charge-pairing mechanisms are of primary importance in attraction and complexation of the redox partners, hydrophobic and van der Waals cohesion forces play a minor role in docking events. Due to catalytic plasticity of P450 enzymes, there is considerable promise in biotechnological applications. Here, deeper insight into the mechanistic basis of the redox machinery will permit optimization of redox processes via directed evolution and DNA shuffling. Thus, creation of hybrid systems by fusion of the modified heme domain of P450s with proteinaceous electron carriers helps obviate the tedious reconstitution procedure and induces novel activities. Also, P450-based amperometric biosensors may open new vistas in pharmaceutical and clinical implementation and environmental monitoring.

Using SILAC proteomics to investigate the effect of the mycotoxin, alternariol, in the human H295R steroidogenesis model

The mycotoxin alternariol (AOH) is an important contaminant of fruits and cereal products. The current study sought to address the effect of a non-toxic AOH concentration on the proteome of the steroidogenic H295R cell model. Quantitative proteomics based on stable isotope labeling by amino acids in cell culture (SILAC) coupled to 1D-SDS-PAGE-LC-MS/MS was applied to subcellular-enriched protein samples. Gene ontology (GO) and ingenuity pathway analysis (IPA) were further carried out for functional annotation and identification of protein interaction networks. Furthermore, the effect of AOH on apoptosis and cell cycle distribution was also determined by the use of flow cytometry analysis. This work identified 22 proteins that were regulated significantly. The regulated proteins are those involved in early stages of steroid biosynthesis (SOAT1, NPC1, and ACBD5) and C21-steroid hormone metabolism (CYP21A2 and HSD3B1). In addition, several proteins known to play a role in cellular assembly, organization, protein synthesis, and cell cycle were regulated. These findings provide a new framework for studying the mechanisms by which AOH modulates steroidogenesis in H295R cell model.

Oxidative stress and adrenocortical insufficiency

Maintenance of redox balance is essential for normal cellular functions. Any perturbation in this balance due to increased reactive oxygen species (ROS) leads to oxidative stress and may lead to cell dysfunction/damage/death. Mitochondria are responsible for the majority of cellular ROS production secondary to electron leakage as a consequence of respiration. Furthermore, electron leakage by the cytochrome P450 enzymes may render steroidogenic tissues acutely vulnerable to redox imbalance. The adrenal cortex, in particular, is well supplied with both enzymatic (glutathione peroxidases and peroxiredoxins) and non-enzymatic (vitamins A, C and E) antioxidants to cope with this increased production of ROS due to steroidogenesis. Nonetheless oxidative stress is implicated in several potentially lethal adrenal disorders including X-linked adrenoleukodystrophy, triple A syndrome and most recently familial glucocorticoid deficiency. The finding of mutations in antioxidant defence genes in the latter two conditions highlights how disturbances in redox homeostasis may have an effect on adrenal steroidogenesis.

Discovery of potential biomarkers in exhaled breath for diagnosis of type 2 diabetes mellitus based on GC-MS with metabolomics

Eight breath biomarkers of T2DM were discovered by a new SPME-GC-MS based metabolic profiling tool.

Genome-wide association study of chronic hepatitis B virus infection reveals a novel candidate risk allele on 11q22.3

BACKGROUND

Hepatitis B virus (HBV) affects millions of people worldwide. While some people are able to clear the virus following the first encounter, those who develop chronic infection manifest remarkable clinical heterogeneity that ranges from asymptomatic carrier state to cirrhosis and hepatocellular carcinoma. Despite extensive studies, little is known about genetic host factors that influence the outcome of chronic HBV infection. Thus, we conducted this study to investigate the genetic risk of developing active liver disease among chronic carriers of HBV.

METHODS

In this study, we conducted a genome-wide association study (GWAS) on a cohort of patients with chronic HBV infection.

RESULTS

One particular SNP that is 16 kb upstream of Ferredoxin 1 was found to have an association with complicated chronic HBV infection (cirrhosis and hepatocellular carcinoma) that reached GWAS significance, and was successfully validated on an independent set of samples.

CONCLUSIONS

This first GWAS in an Arab population further demonstrates the utility of this approach in elucidating the genetic risk of HBV infection-related complications and highlights the advantage of conducting GWAS in different ethnicities to achieve that goal.

Human ferredoxin-2 displays a unique conformational change

Human ferredoxin-1 (hFd1) and human ferredoxin-2 (hFd2) share high sequence similarity but serve on distinct cellular pathways. A unique conformational change is observed when holo hFd2 is warmed to physiological temperatures, or higher. Enzymatic studies show that this conformational change causes the increase of affinity between hFd2 and adrenodoxin reductase. No such change was observed for hFd1, which may contribute to the distinct cellular functions of hFd1 and hFd2 under physiological conditions.

[2Fe-2S] proteins in Chlorosomes: redox properties of CsmI, CsmJ, and CsmX of the Chlorosome envelope of Chlorobaculum tepidum

The chlorosome envelope of Chlorobaculum tepidum contains 10 polypeptides, three of which, CsmI, CsmJ, and CsmX, have an adrenodoxin-like domain harboring a single [2Fe-2S] cluster. Mutants that produced chlorosomes containing two, one, or none of these Fe-S proteins were constructed [Li, H., et al. (2013) Biochemistry 52, preceding paper in this issue ( DOI: 10.1021/bi301454g )]. The electron paramagnetic resonance (EPR) spectra, g values, and line widths of the Fe-S clusters in individual CsmI, CsmJ, and CsmX proteins were obtained from studies with isolated chlorosomes. The Fe-S clusters in these proteins were characterized by EPR and could be differentiated on the basis of their g values and line widths. The EPR spectrum of wild-type chlorosomes could be simulated by a 1:1 admixture of the CsmI and CsmJ spectra. No contribution of CsmX to the EPR spectrum of chlorosomes was observed because of its low abundance. In chlorosomes that contained only CsmI or CsmJ, the midpoint potential of the [2Fe-2S] clusters was -205 or 8 mV, respectively; the midpoint potential of the [2Fe-2S] cluster in CsmX was estimated to be more oxidizing than -180 mV. In wild-type chlorosomes, the midpoint potentials of the [2Fe-2S] clusters were -348 mV for CsmI and 92 mV for CsmJ. The lower potential for CsmI in the presence of CsmJ, and the higher potential for CsmJ in the presence of CsmI, were attributed to interactions that occur when these proteins form complexes in the chlorosome envelope. The redox properties of CsmI and CsmJ are consistent with their proposed participation in the transfer of electrons to and from quenchers of energy transfer in chlorosomes.

A prevalent and three novel mutations in CYP11B1 gene identified in Chinese patients with 11-beta hydroxylase deficiency

11β-Hydroxylase deficiency (11β-OHD), caused by CYP11B1 mutations, is characterized by hyporeninemic, hypokalemic hypertension and hyperandrogenism. We identified a prevalent and three novel mutations of CYP11B1 gene in nine patients with classic 11β-OHD.

SUBJECTS AND METHODS

Nine patients with 11β-OHD from unrelated families were recruited. The complications of 11β-OHD occurred in three patients who never received glucocorticoid treatment. CYP11B1 gene was sequenced and 11β-hydroxylase enzymatic activities were assessed in vitro. A haplotype analysis was performed to determine a common ancestor for those subjects who carried the same p.R454C mutation.

RESULTS

CYP11B1 gene mutations were identified in all patients, with a prevalent (p.R454C) and three novel mutations (p.V148G, IVS7-9C>A, c.1359_1360insG). The p.R141X, p.V148G, c.1359_1360insG and p.R454C mutations retained 4.9%, 3.9%, 3.7%, 4.5% of residual enzymatic activity, respectively. Five of nine patients carried p.R454C mutation, which was only reported in Chinese 11OHD patients. Haplotype analysis showed that this mutation might be inherited from a common ancestor.

CONCLUSION

The enzymatic activities for p.R141X, p.V148G, c.1359_1360insG and p.R454C mutants were almost completely abolished, which corresponds to classic form of 11β-OHD. The observations of a prevalent mutation and three novel mutations might have potential clinical utility for genetic counseling and prenatal diagnosis in Chinese 11β-OHD patients.

Functional characterization of Fdx1: evidence for an evolutionary relationship between P450-type and ISC-type ferredoxins

Ferredoxins are ubiquitous proteins with electron transfer activity involved in a variety of biological processes. In this work, we investigated the characteristics and function of Fdx1 from Sorangium cellulosum So ce56 by using a combination of bioinformatics and of biochemical/biophysical approaches. We were able to experimentally confirm a role of Fdx1 in the iron-sulfur cluster biosynthesis by in vitro reduction studies with cluster-loaded So ce56 IscU and by transfer studies of the cluster from the latter protein to apo-aconitase A. Moreover, we found that Fdx1 can replace mammalian adrenodoxin in supporting the activity of bovine CYP11A1. This makes S. cellulosum Fdx1 the first prokaryotic ferredoxin reported to functionally interact with this mammalian enzyme. Although the interaction with CYP11A1 is non-physiological, this is-to the best of our knowledge-the first study to experimentally prove the activity of a postulated ISC-type ferredoxin in both the ISC assembly and a cytochrome P450 system. This proves that a single ferredoxin can be structurally able to provide electrons to both cytochromes P450 and IscU and thus support different biochemical processes. Combining this finding with phylogenetic and evolutionary trace analyses led us to propose the evolution of eukaryotic mitochondrial P450-type ferredoxins and ISC-type ferredoxins from a common prokaryotic ISC-type ancestor.