Membrane-Bound Redox Enzyme Cytochrome bd-I Promotes Carbon Monoxide-Resistant Escherichia coli Growth and Respiration

The terminal oxidases of bacterial aerobic respiratory chains are redox-active electrogenic enzymes that catalyze the four-electron reduction of O2 to 2H2O taking out electrons from quinol or cytochrome c. Living bacteria often deal with carbon monoxide (CO) which can act as both a signaling molecule and a poison. Bacterial terminal oxidases contain hemes; therefore, they are potential targets for CO. However, our knowledge of this issue is limited and contradictory. Here, we investigated the effect of CO on the cell growth and aerobic respiration of three different Escherichia coli mutants, each expressing only one terminal quinol oxidase: cytochrome bd-I, cytochrome bd-II, or cytochrome bo3. We found that following the addition of CO to bd-I-only cells, a minimal effect on growth was observed, whereas the growth of both bd-II-only and bo3-only strains was severely impaired. Consistently, the degree of resistance of aerobic respiration of bd-I-only cells to CO is high, as opposed to high CO sensitivity displayed by bd-II-only and bo3-only cells consuming O2. Such a difference between the oxidases in sensitivity to CO was also observed with isolated membranes of the mutants. Accordingly, O2 consumption of wild-type cells showed relatively low CO sensitivity under conditions favoring the expression of a bd-type oxidase.

Comparison of insect and human cytochrome b561 proteins: Insights into candidate ferric reductases in insects

Cytochrome b561 (cytb561) proteins comprise a family of transmembrane oxidoreductases that transfer single electrons across a membrane. Most eukaryotic species, including insects, possess multiple cytb561 homologs. To learn more about this protein family in insects, we carried out a bioinformatics-based investigation of cytb561 family members from nine species representing eight insect orders. We performed a phylogenetic analysis to classify insect cytb561 ortholog groups. We then conducted sequence analyses and analyzed protein models to predict structural elements that may impact the biological functions and localization of these proteins, with a focus on possible ferric reductase activity. Our study revealed three ortholog groups, designated CG1275, Nemy, and CG8399, and a fourth group of less-conserved genes. We found that CG1275 and Nemy proteins are similar to a human ferric reductase, duodenal cytochrome b561 (Dcytb), and have many conserved amino acid residues that function in substrate binding in Dcytb. Notably, CG1275 and Nemy proteins contain a conserved histidine and other residues that play a role in ferric ion reduction by Dcytb. Nemy proteins were distinguished by a novel cysteine-rich cytoplasmic loop sequence. CG8399 orthologs are similar to a putative ferric reductase in humans, stromal cell-derived receptor 2. Like other members of the CYBDOM class of cytb561 proteins, these proteins contain reeler, DOMON, and cytb561 domains. Drosophila melanogaster CG8399 is the only insect cytb561 with known ferric reductase activity. Our investigation of the DOMON domain in CG8399 proteins revealed a probable heme-binding site and a possible site for ferric reduction. The fourth group includes a subgroup of proteins with a conserved "KXXXXKXH" non-cytoplasmic loop motif that may be a substrate binding site and is present in a potential ferric reductase, human tumor suppressor cytochrome b561. This study provides a foundation for future investigations of the biological functions of cytb561 genes in insects.

Generation of Membrane Potential by Cytochrome bd

An overview of current notions on the mechanism of generation of a transmembrane electric potential difference (Δψ) during the catalytic cycle of a bd-type triheme terminal quinol oxidase is presented in this work. It is suggested that the main contribution to Δψ formation is made by the movement of H+ across the membrane along the intra-protein hydrophilic proton-conducting pathway from the cytoplasm to the active site for oxygen reduction of this bacterial enzyme.

Rubredoxin 1 promotes the proper folding of D1 and is not required for heme b559 assembly in Chlamydomonas photosystem II

Photosystem II (PSII), the water:plastoquinone oxidoreductase of oxygenic photosynthesis, contains a heme b₅₅₉ iron whose axial ligands are provided by histidine residues from the α (PsbE) and β (PsbF) subunits. PSII assembly depends on accessory proteins that facilitate the step-wise association of its protein and pigment components into a functional complex, a process that is challenging to study due to the low accumulation of assembly intermediates. Here, we examined the putative role of the iron[1Fe-0S]-containing protein rubredoxin 1 (RBD1) as an assembly factor for cytochrome b₅₅₉, using the RBD1-lacking 2pac mutant from Chlamydomonas reinhardtii, in which the accumulation of PSII was rescued by the inactivation of the thylakoid membrane FtsH protease. To this end, we constructed the double mutant 2pac ftsh1-1, which harbored PSII dimers that sustained its photoautotrophic growth. We purified PSII from the 2pac ftsh1-1 background and found that α and β cytochrome b₅₅₉ subunits are still present and coordinate heme b₅₅₉ as in the WT. Interestingly, immunoblot analysis of dark- and low light-grown 2pac ftsh1-1 showed the accumulation of a 23-kDa fragment of the D1 protein, a marker typically associated with structural changes resulting from photodamage of PSII. Its cleavage occurs in the vicinity of a nonheme iron which binds to PSII on its electron acceptor side. Altogether, our findings demonstrate that RBD1 is not required for heme b₅₅₉ assembly and point to a role for RBD1 in promoting the proper folding of D1, possibly via delivery or reduction of the nonheme iron during PSII assembly.

DDX17 induces epithelial-mesenchymal transition and metastasis through the miR-149-3p/CYBRD1 pathway in colorectal cancer

DEAD box helicase 17 (DDX17) has been reported to be involved in the initiation and development of several cancers. However, the functional role and mechanisms of DDX17 in colorectal cancer (CRC) malignant progression and metastasis remain unclear. Here, we reported that DDX17 expression was increased in CRC tissues compared with noncancerous mucosa tissues and further upregulated in CRC liver metastasis compared with patient-paired primary tumors. High levels of DDX17 were significantly correlated with aggressive phenotypes and worse clinical outcomes in CRC patients. Ectopic expression of DDX17 promoted cell migration and invasion in vitro and in vivo, while the opposite results were obtained in DDX17-deficient CRC cells. We identified miR-149-3p as a potential downstream miRNA of DDX17 through RNA sequencing analysis, and miR-149-3p displayed a suppressive effect on the metastatic potential of CRC cells. We demonstrated that CYBRD1 (a ferric reductase that contributes to dietary iron absorption) was a direct target of miR-149-3p and that miR-149-3p was required for DDX17-mediated regulation of CYBRD1 expression. Moreover, DDX17 contributed to the metastasis and epithelial to mesenchymal transition (EMT) of CRC cells via downregulation of miR-149-3p, which resulted in increased CYBRD1 expression. In conclusion, our findings not only highlight the significance of DDX17 in the aggressive development and prognosis of CRC patients, but also reveal a novel mechanism underlying DDX17-mediated CRC cell metastasis and EMT progression through manipulation of the miR-149-3p/CYBRD1 pathway.

Protein encapsulation within the internal cavity of a bacterioferritin

The thermal and chemical stability of 24mer ferritins has led to attempts to exploit their naturally occurring nanoscale (8 nm) internal cavities for biotechnological applications. An area of increasing interest is the encapsulation of molecules either for medical or biocatalysis applications. Encapsulation requires ferritin dissociation, typically induced using high temperature or acidic conditions (pH ≥ 2), which generally precludes the inclusion of fragile cargo such as proteins or peptide fragments. Here we demonstrate that minimizing salt concentration combined with adjusting the pH to ≤8.5 (i.e. low proton/metal ion concentration) reversibly shifts the naturally occurring equilibrium between dimeric and 24meric assemblies of Escherichia coli bacterioferritin (Bfr) in favour of the disassembled form. Interconversion between the different oligomeric forms of Bfr is sufficiently slow under these conditions to allow the use of size exclusion chromatography to obtain wild type protein in the purely dimeric and 24meric forms. This control over association state was exploited to bind heme at natural sites that are not accessible in the assembled protein. The potential for biotechnological applications was demonstrated by the encapsulation of a small, acidic [3Fe-4S] cluster-containing ferredoxin within the Bfr internal cavity. The capture of ∼4-6 negatively charged ferredoxin molecules per cage indicates that charge complementarity with the inner protein surface is not an essential determinant of successful encapsulation.

Preparations of Terminal Oxidase Cytochrome bd-II Isolated from Escherichia coli Reveal Significant Hydrogen Peroxide Scavenging Activity

Cytochrome bd-II is one of the three terminal quinol oxidases of the aerobic respiratory chain of Escherichia coli. Preparations of the detergent-solubilized untagged bd-II oxidase isolated from the bacterium were shown to scavenge hydrogen peroxide (H2O2) with high rate producing molecular oxygen (O₂). Addition of H2O2 to the same buffer that does not contain enzyme or contains thermally denatured cytochrome bd-II does not lead to any O2 production. The latter observation rules out involvement of adventitious transition metals bound to the protein. The H2O2-induced O2 production is not susceptible to inhibition by N-ethylmaleimide (the sulfhydryl binding compound), antimycin A (the compound that binds specifically to a quinol binding site), and CO (diatomic gas that binds specifically to the reduced heme d). However, O2 formation is inhibited by cyanide (IC₅₀ = 4.5 ± 0.5 µM) and azide. Addition of H2O2 in the presence of dithiothreitol and ubiquinone-1 does not inactivate cytochrome bd-II and apparently does not affect the O2 reductase activity of the enzyme. The ability of cytochrome bd-II to detoxify H2O2 could play a role in bacterial physiology by conferring resistance to the peroxide-mediated stress.

Tandem gene amplification restores photosystem II accumulation in cytochrome b559 mutants of cyanobacteria

Cytochrome (Cyt) b₅₅₉ is a key component of the photosystem II complex (PSII) that is essential for its proper functioning and assembly. Site-directed mutants of the model cyanobacterium Synechocystis sp. PCC6803 with mutated heme axial ligands of Cyt b₅₅₉ have little PSII and are therefore unable to grow photoautotrophically. Here we describe two types of Synechocystis autotrophic transformants that retained the same mutations in Cyt b₅₅₉ but are able to accumulate PSII and grow photoautotrophically. Whole-genome sequencing revealed that all of these autotrophic transformants carried a variable number of tandem repeats (from 5 to 15) of chromosomal segments containing the psbEFLJ operon. RNA-seq analysis showed greatly increased transcript levels of the psbEFLJ operon in these autotrophic transformants. Multiple copies of the psbEFLJ operon in these transformants were only maintained during autotrophic growth, while its copy numbers gradually decreased under photoheterotrophic conditions. Two-dimensional PAGE analysis of membrane proteins revealed a strong deficiency in PSII complexes in the Cyt b₅₅₉ mutants that was reversed in the autotrophic transformants. These results illustrate how tandem gene amplification restores PSII accumulation and photoautotrophic growth in Cyt b₅₅₉ mutants of cyanobacteria, and may serve as an important adaptive mechanism for cyanobacterial survival.

miR-423-3p activates FAK signaling pathway to drive EMT process and tumor growth in lung adenocarcinoma through targeting CYBRD1

BACKGROUND

Lung adenocarcinoma (LUAD) is a malignant tumor with a high fatality rate and poor overall survival, while molecular targets diagnosing and alleviating lung cancer remain inadequate.

METHODS

In this article, we highlighted the upregulation of microRNA-423-3p (miR-423-3p) in LUAD, especially in smokers aged over 40, and revealed that the high expression of miR-423-3p was significantly associated with smoker, age, and pathologic stage of LUAD patients.

RESULTS

Moreover, overexpressing miR-423-3p could facilitate LUAD cell proliferation, invasion, adhesion, and epithelial-mesenchymal transition (EMT) process, while depleted miR-423-3p caused repressive influence upon it. Mechanically, we identified that miR-423-3p could activate FAK signaling pathway through binding to the 3'-UTR of cytochrome B reductase 1 (CYBRD1). Furthermore, we demonstrated that CYBRD1 was lowly expressed in LUAD, and miR-423-3p overexpression could rescue the impairment of LUAD cell proliferation, invasion, adhesion, and EMT caused by CYBRD1 depletion. Noticeably, miR-423-3p depletion efficiently hindered LUAD tumor growth in vivo.

CONCLUSION

Collectively, our findings demonstrated that miR-423-3p/CYBRD1 axis could be regarded as a promising biomarker to alleviate the poor LUAD prognosis.

Bacterial Oxidases of the Cytochrome bd Family: Redox Enzymes of Unique Structure, Function, and Utility As Drug Targets

Significance: Cytochrome bd is a ubiquinol:oxygen oxidoreductase of many prokaryotic respiratory chains with a unique structure and functional characteristics. Its primary role is to couple the reduction of molecular oxygen, even at submicromolar concentrations, to water with the generation of a proton motive force used for adenosine triphosphate production. Cytochrome bd is found in many bacterial pathogens and, surprisingly, in bacteria formally denoted as anaerobes. It endows bacteria with resistance to various stressors and is a potential drug target. Recent Advances: We summarize recent advances in the biochemistry, structure, and physiological functions of cytochrome bd in the light of exciting new three-dimensional structures of the oxidase. The newly discovered roles of cytochrome bd in contributing to bacterial protection against hydrogen peroxide, nitric oxide, peroxynitrite, and hydrogen sulfide are assessed. Critical Issues: Fundamental questions remain regarding the precise delineation of electron flow within this multihaem oxidase and how the extraordinarily high affinity for oxygen is accomplished, while endowing bacteria with resistance to other small ligands. Future Directions: It is clear that cytochrome bd is unique in its ability to confer resistance to toxic small molecules, a property that is significant for understanding the propensity of pathogens to possess this oxidase. Since cytochrome bd is a uniquely bacterial enzyme, future research should focus on harnessing fundamental knowledge of its structure and function to the development of novel and effective antibacterial agents.

Urinary 8-iso PGF2α and 2,3-dinor-8-iso PGF2α can be indexes of colitis-associated colorectal cancer in mice

Early diagnosis of colorectal cancer is needed to reduce the mortal consequence by cancer. Lipid mediators play critical role in progression of colitis and colitis-associated colon cancer (CAC) and some of their metabolites are excreted in urine. Here, we attempted to find novel biomarkers in urinary lipid metabolite of a murine model of CAC. Mice were received single administration of azoxymethane (AOM) and repeated administration of dextran sulfate sodium (DSS). Lipid metabolites in their urine was measured by liquid chromatography mass spectrometry and their colon was collected to perform morphological study. AOM and DSS caused inflammation and tumor formation in mouse colon. Liquid chromatography mass spectrometry-based comprehensive analysis of lipid metabolites showed that cyclooxygenase-mediated arachidonic acid (AA) metabolites, prostaglandins, and reactive oxygen species (ROS)-mediated AA metabolites, isoprostanes, were predominantly increased in the urine of tumor-bearing mice. Among that, urinary prostaglandin (PG)E2 metabolite tetranor-PGEM and PGD2 metabolite tetranor-PGDM were significantly increased in both of urine collected at the acute phase of colitis and the carcinogenesis phase. On the other hand, two F2 isoprostanes (F2-IsoPs), 8-iso PGF2α and 2,3-dinor-8-iso PGF2α, were significantly increased only in the carcinogenesis phase. Morphological study showed that infiltrated monocytes into tumor mass strongly expressed ROS generator NADPH (p22phox). These observations suggest that urinary 8-iso PGF2α and 2,3-dinor-8-iso PGF2α can be indexes of CAC.

Controlling Protein Nanocage Assembly with Hydrostatic Pressure

Controlling the assembly and disassembly of nanoscale protein cages for the capture and internalization of protein or non-proteinaceous components is fundamentally important to a diverse range of bionanotechnological applications. Here, we study the reversible, pressure-induced dissociation of a natural protein nanocage, E. coli bacterioferritin (Bfr), using synchrotron radiation small-angle X-ray scattering (SAXS) and circular dichroism (CD). We demonstrate that hydrostatic pressures of 450 MPa are sufficient to completely dissociate the Bfr 24-mer into protein dimers, and the reversibility and kinetics of the reassembly process can be controlled by selecting appropriate buffer conditions. We also demonstrate that the heme B prosthetic group present at the subunit dimer interface influences the stability and pressure lability of the cage, despite its location being discrete from the interdimer interface that is key to cage assembly. This indicates a major cage-stabilizing role for heme within this family of ferritins.

Agrobacterium tumefaciens ferritins play an important role in full virulence through regulating iron homeostasis and oxidative stress survival

Ferritins are a large family of iron storage proteins, which are used by bacteria and other organisms to avoid iron toxicity and as a safe iron source in the cytosol. Agrobacterium tumefaciens, a phytopathogen, has two ferritin-encoding genes: atu2771 and atu2477. Atu2771 is annotated as a Bfr-encoding gene (Bacterioferritin, Bfr) and atu2477 as a Dps-encoding gene (DNA binding protein from starved cells, Dps). Three deletion mutants (Δbfr, Δdps, and bfr-dps double-deletion mutant ΔbdF) of these two ferritin-encoding genes were constructed to investigate the effects of ferritin deficiency on the iron homeostasis, oxidative stress resistance, and pathogenicity of A. tumefaciens. Deficiency of two ferritins affects the growth of A. tumefaciens under iron starvation and excess. When supplied with moderate iron, the growth of A. tumefaciens is not affected by the deficiency of ferritin. Deficiency of ferritin significantly reduces iron accumulation in the cells of A. tumefaciens, but the effect of Bfr deficiency on iron accumulation is severer than Dps deficiency and the double mutant ΔbdF has the least intracellular iron content. All three ferritin-deficient mutants showed a decreased tolerance to 3 mM H2 O2 in comparison with the wild type. The tumour induced by each of three ferritin-deficient mutants is less than that of the wild type. Complementation reversed the effects of ferritin deficiency on the growth, iron homeostasis, oxidative stress resistance, and tumorigenicity of A. tumefaciens. Therefore, ferritin plays an important role in the pathogenesis of A. tumefaciens through regulating iron homeostasis and oxidative stress survival.

Constructing artificial respiratory chain in polymer compartments: Insights into the interplay between bo3 oxidase and the membrane

Cytochrome bo3 ubiquinol oxidase is a transmembrane protein, which oxidizes ubiquinone and reduces oxygen, while pumping protons. Apart from its combination with F1Fo-ATPase to assemble a minimal ATP regeneration module, the utility of the proton pump can be extended to other applications in the context of synthetic cells such as transport, signaling, and control of enzymatic reactions. In parallel, polymers have been speculated to be phospholipid mimics with respect to their ability to self-assemble in compartments with increased stability. However, their usability as interfaces for complex membrane proteins has remained questionable. In the present work, we optimized a fusion/electroformation approach to reconstitute bo3 oxidase in giant unilamellar vesicles made of PDMS-g-PEO and/or phosphatidylcholine (PC). This enabled optical access, while microfluidic trapping allowed for online analysis of individual vesicles. The tight polymer membranes and the inward oriented enzyme caused 1 pH unit difference in 30 min, with an initial rate of 0.35 pH·min-1 To understand the interplay in these composite systems, we studied the relevant mechanical and rheological membrane properties. Remarkably, the proton permeability of polymer/lipid hybrids decreased after protein insertion, while the latter also led to a 20% increase of the polymer diffusion coefficient in polymersomes. In addition, PDMS-g-PEO increased the activity lifetime and the resistance to free radicals. These advantageous properties may open diverse applications, ranging from cell-free biotechnology to biomedicine. Furthermore, the presented study serves as a comprehensive road map for studying the interactions between membrane proteins and synthetic membranes, which will be fundamental for the successful engineering of such hybrid systems.

Characterization of the Fe metalloproteome of a ubiquitous marine heterotroph, Pseudoalteromonas (BB2-AT2): multiple bacterioferritin copies enable significant Fe storage

Fe is a critical nutrient to the marine biological pump, which is the process that exports photosynthetically fixed carbon in the upper ocean to the deep ocean. Fe limitation controls photosynthetic activity in major regions of the oceans, and the subsequent degradation of exported photosynthetic material is facilitated particularly by marine heterotrophic bacteria. Despite their importance in the carbon cycle and the scarcity of Fe in seawater, the Fe requirements, storage and cytosolic utilization of these marine heterotrophs has been less studied. Here, we characterized the Fe metallome of Pseudoalteromonas (BB2-AT2). We found that with two copies of bacterioferritin (Bfr), Pseudoalteromonas possesses substantial capacity for luxury uptake of Fe. Fe : C in the whole cell metallome was estimated (assuming C : P stoichiometry ∼51 : 1) to be between ∼83 μmol : mol Fe : C, ∼11 fold higher than prior marine bacteria surveys. Under these replete conditions, other major cytosolic Fe-associated proteins were observed including superoxide dismutase (SodA; with other metal SOD isoforms absent under Fe replete conditions) and catalase (KatG) involved in reactive oxygen stress mitigation and aconitase (AcnB), succinate dehydrogenase (FrdB) and cytochromes (QcrA and Cyt1) involved in respiration. With the aid of singular value decomposition (SVD), we were able to computationally attribute peaks within the metallome to specific metalloprotein contributors. A putative Fe complex TonB transporter associated with the closely related Alteromonas bacterium was found to be abundant within the Pacific Ocean mesopelagic environment. Despite the extreme scarcity of Fe in seawater, the marine heterotroph Pseudoalteromonas has expansive Fe storage capacity and utilization strategies, implying that within detritus and sinking particles environments, there is significant opportunity for Fe acquisition. Together these results imply an evolved dedication of marine Pseudoalteromonas to maintaining an Fe metalloproteome, likely due to its dependence on Fe-based respiratory metabolism.

Broad Specificity of Amino Acid Chemoreceptor CtaA of Pseudomonas fluorescens Is Afforded by Plasticity of Its Amphipathic Ligand-Binding Pocket

Motile bacteria follow gradients of nutrients or other environmental cues. Many bacterial chemoreceptors that sense exogenous amino acids contain a double Cache (dCache; calcium channels and chemotaxis receptors) ligand-binding domain (LBD). A growing number of studies suggest that broad-specificity dCache-type receptors that sense more than one amino acid are common. Here, we present an investigation into the mechanism by which the dCache LBD of the chemoreceptor CtaA from a plant growth-promoting rhizobacterium, Pseudomonas fluorescens, recognizes several chemically distinct amino acids. We established that amino acids that signal by directly binding to the CtaA LBD include ones with aliphatic (l-alanine, l-proline, l-leucine, l-isoleucine, l-valine), small polar (l-serine), and large charged (l-arginine) side chains. We determined the structure of CtaA LBD in complex with different amino acids, revealing that its ability to recognize a range of structurally and chemically distinct amino acids is afforded by its easily accessible plastic pocket, which can expand or contract according to the size of the ligand side chain. The amphipathic character of the pocket enables promiscuous interactions with both polar and nonpolar amino acids. The results not only clarify the means by which various amino acids are recognized by CtaA but also reveal that a conserved mobile lid over the ligand-binding pocket adopts the same conformation in all complexes, consistent with this being an important and invariant part of the signaling mechanism.

The carboxy-terminal insert in the Q-loop is needed for functionality of Escherichia coli cytochrome bd-I

Cytochrome bd, a component of the prokaryotic respiratory chain, is important under physiological stress and during pathogenicity. Electrons from quinol substrates are passed on via heme groups in the CydA subunit and used to reduce molecular oxygen. Close to the quinol binding site, CydA displays a periplasmic hydrophilic loop called Q-loop that is essential for quinol oxidation. In the carboxy-terminal part of this loop, CydA from Escherichia coli and other proteobacteria harbors an insert of ~60 residues with unknown function. In the current work, we demonstrate that growth of the multiple-deletion strain E. coli MB43∆cydA (∆cydA∆cydB∆appB∆cyoB∆nuoB) can be enhanced by transformation with E. coli cytochrome bd-I and we utilize this system for assessment of Q-loop mutants. Deletion of the cytochrome bd-I Q-loop insert abolished MB43∆cydA growth recovery. Swapping the cytochrome bd-I Q-loop for the Q-loop from Geobacillus thermodenitrificans or Mycobacterium tuberculosis CydA, which lack the insert, did not enhance the growth of MB43∆cydA, whereas swapping for the Q-loop from E. coli cytochrome bd-II recovered growth. Alanine scanning experiments identified the cytochrome bd-I Q-loop insert regions Ile³¹⁸-Met³²², Gln³³⁸-Asp³⁴², Tyr³⁵³-Leu³⁵⁷, and Thr³⁶⁸-Ile³⁷² as important for enzyme functionality. Those mutants that completely failed to recover growth of MB43∆cydA also lacked oxygen consumption activity and heme absorption peaks. Moreover, we were not able to isolate cytochrome bd-I from these inactive mutants. The results indicate that the cytochrome bd Q-loop exhibits low plasticity and that the Q-loop insert in E. coli is needed for complete, stable, assembly of cytochrome bd-I.

Differential effects of NaCl and Na2SO4 on the halophyte Prosopis strombulifera are explained by different responses of photosynthesis and metabolism

Prosopis strombulifera (Lam.) Benth. is a halophytic shrub found in highly saline soils in Argentina, with high tolerance against NaCl but strong growth inhibition by Na₂SO_4. In the present study, the differences in the physiological responses caused by these salts and an iso-osmotic combination thereof on photosynthesis, mineral composition and metabolism were analyzed. Na₂SO₄ treated plants were the most affected by salinity, showing a significant decrease in several photosynthetic parameters. Proline and cysteine accumulated significantly in the plants in response to salt stress. These results show by the first time that the SO₄^2- anion is triggering damage in the photosynthetic apparatus and consequently affecting the photosynthetic process, which may explain the strong growth inhibition in these plants at high salinity. Moreover, the SO₄^2- anion provoke challenges in the incorporation of nutrients, decreasing the levels of K, Ca, P and Mg, and inducing a strong antioxidant activity in P. strombulifera.

An efficient, step-economical strategy for the design of functional metalloproteins

The bottom-up design and construction of functional metalloproteins remains a formidable task in biomolecular design. Although numerous strategies have been used to create new metalloproteins, pre-existing knowledge of the tertiary and quaternary protein structure is often required to generate suitable platforms for robust metal coordination and activity. Here we report an alternative and easily implemented approach (metal active sites by covalent tethering or MASCoT) in which folded protein building blocks are linked by a single disulfide bond to create diverse metal coordination environments within evolutionarily naive protein-protein interfaces. Metalloproteins generated using this strategy uniformly bind a wide array of first-row transition metal ions (MnII, FeII, CoII, NiII, CuII, ZnII and vanadyl) with physiologically relevant thermodynamic affinities (dissociation constants ranging from 700 nM for MnII to 50 fM for CuII). MASCoT readily affords coordinatively unsaturated metal centres-including a penta-His-coordinated non-haem Fe site-and well-defined binding pockets that can accommodate modifications and enable coordination of exogenous ligands such as nitric oxide to the interfacial metal centre.

The proton pumping bo oxidase from Vitreoscilla

The cytochrome bo3 quinol oxidase from Vitreoscilla (vbo3) catalyses oxidation of ubiquinol and reduction of O2 to H2O. Data from earlier studies suggested that the free energy released in this reaction is used to pump sodium ions instead of protons across a membrane. Here, we have studied the functional properties of heterologously expressed vbo3 with a variety of methods. (i) Following oxygen consumption with a Clark-type electrode, we did not observe a measurable effect of Na+ on the oxidase activity of purified vbo3 solubilized in detergent or reconstituted in liposomes. (ii) Using fluorescent dyes, we find that vbo3 does not pump Na+ ions, but H+ across the membrane, and that H+-pumping is not influenced by the presence of Na+. (iii) Using an oxygen pulse method, it was found that 2 H+/e- are ejected from proteoliposomes, in agreement with the values found for the H+-pumping bo3 oxidase of Escherichia coli (ecbo3). This coincides with the interpretation that 1 H+/e- is pumped across the membrane and 1 H+/e- is released during quinol oxidation. (iv) When the electron transfer kinetics of vbo3 upon reaction with oxygen were followed in single turnover experiments, a similar sequence of reaction steps was observed as reported for the E. coli enzyme and none of these reactions was notably affected by the presence of Na+. Overall the data show that vbo3 is a proton pumping terminal oxidase, behaving similarly to the Escherichia coli bo3 quinol oxidase.

Site-directed mutagenesis of two amino acid residues in cytochrome b559 α subunit that interact with a phosphatidylglycerol molecule (PG772) induces quinone-dependent inhibition of photosystem II activity

X-ray crystallographic analysis (1.9-Å resolution) of the cyanobacterial photosystem II (PSII) dimer showed the presence of five phosphatidylglycerol (PG) molecules per reaction center. One of the PG molecules, PG772, is located in the vicinity of the Q_B-binding site. To investigate the role of PG772 in PSII, we performed site-directed mutagenesis in the cytochrome (Cyt) b₅₅₉ α subunit of Synechocystis sp. PCC 6803 to change two amino acids, Thr-5 and Ser-11, which interact with PG772. The photosynthetic activity of intact cells was slightly lower in all mutants than that of cells in the control strain; however, the oxygen-evolving PSII activity was decreased markedly in cells of mutants, as measured using artificial quinones (such as p-benzoquinone). Furthermore, electron transport from Q_A to Q_B was inhibited in mutants incubated with quinones, particularly under high-intensity light conditions. Lipid analysis of purified PSII showed approximately one PG molecule per reaction center, presumably PG772, was lost in the PSII dimer from the T5A and S11A mutants compared with that in the PSII dimer from the control strain. In addition, protein analysis of monomer and dimer showed decreased levels of PsbV and PsbU extrinsic proteins in the PSII monomer purified from T5A and S11A mutants. These results suggest that site-directed mutagenesis of Thr-5 and Ser-11, which presumably causes the loss of PG772, induces quinone-dependent inhibition of PSII activity under high-intensity light conditions and destabilizes the binding of extrinsic proteins to PSII.

Antimycin A inhibits cytochrome b559-mediated cyclic electron flow within photosystem II

The light reactions of photosynthesis are known to comprise both linear and cyclic electron flow in order to convert light energy into chemical energy in the form of NADPH and ATP. Antimycin A (AA) has been proposed as an inhibitor of ferredoxin-dependent cyclic electron flow around photosystem I (CEF-PSI) in photosynthesis research. However, its precise inhibitory mechanism and target site had not been elucidated yet. Here we show that AA inhibits the cyclic (alternative) electron flow via cytochrome b₅₅₉ (Cyt b₅₅₉) within photosystem II (CEF-PSII). When AA was applied to thylakoid membranes isolated from spinach leaves, the high potential form of Cyt b₅₅₉, which was reduced in the dark, was transformed into the lower potential forms and readily oxidized by molecular oxygen. In the absence of AA, the reduced Cyt b₅₅₉ was oxidized by P680⁺ upon light illumination and re-reduced in the dark, mainly by the electron from the Q_B site on the acceptor side of PSII. In contrast, AA suppressed the oxidation of Cyt b₅₅₉ and induced its reduction under the illumination. This inhibition of Cyt b₅₅₉ oxidation by AA enhanced photoinhibition of PSII. Based on the above results, we propose caution regarding the use of AA for evaluating CEF-PSI per se and concurrently propose that AA provides for new insights into, and interpretations of, the physiological importance of Cyt b₅₅₉, rather than that of CEF-PSI in photosynthetic organisms.

Consequences of structural modifications in cytochrome b559 on the electron acceptor side of Photosystem II

Cytb₅₅₉ in Photosystem II is a heterodimeric b-type cytochrome. The subunits, PsbE and PsbF, consist each in a membrane α-helix. Mutants were previously designed and studied in Thermosynechococcus elongatus (Sugiura et al., Biochim Biophys Acta 1847:276-285, 2015) either in which an axial histidine ligand of the haem-iron was substituted for a methionine, the PsbE/H23M mutant in which the haem was lacking, or in which the haem environment was modified, the PsbE/Y19F and PsbE/T26P mutants. All these mutants remained active showing that the haem has no structural role provided that PsbE and PsbF subunits are present. Here, we have carried on the characterization of these mutants. The following results were obtained: (i) the Y19F mutation hardly affect the E_m of Cytb₅₅₉, whereas the T26P mutation converts the haem into a form with a E_m much below 0 mV (so low that it is likely not reducible by Q_B^-) even in an active enzyme; (ii) in the PsbE/H23M mutant, and to a less extent in PsbE/T26P mutant, the electron transfer efficiency from Q_A^- to Q_B is decreased; (iii) the lower E_m of the Q_A/Q_A^- couple in the PsbE/H23M mutant correlates with a higher production of singlet oxygen; (iv) the superoxide and/or hydroperoxide formation was not increased in the PsbE/H23M mutant lacking the haem, whereas it was significantly larger in the PsbE/T26P. These data are discussed in view of the literature to discriminate between structural and redox roles for the haem of Cytb₅₅₉ in the production of reactive oxygen species.

Intersecting Stories of the Phagocyte NADPH Oxidase and Chronic Granulomatous Disease

Neutrophils serve as the circulating cells that respond early and figure prominently in human host defense to infection and in inflammation in other settings. Optimal oxidant-dependent antimicrobial activity by neutrophils relies on the ability of stimulated phagocytes to utilize a multicomponent NADPH oxidase to generate oxidants. The frequent, severe, and often fatal infections experienced by individuals with chronic granulomatous disease (CGD), an inherited disorder in which one of the NADPH oxidase components is absent or dysfunctional, underscore the link between a functional phagocyte NADPH oxidase and robust host protection against microbial infection.The history of the discovery and characterization of the normal neutrophil NADPH oxidase and the saga of recognizing CGD and its underlying causes together illustrate how the observations of astute clinicians and imaginative basic scientists synergize to forge new understanding of both basic cell biology and pathogenesis of human disease.In this chapter, we review the events in the stepwise evolution of our understanding of the phagocyte NADPH oxidase, both in the context of normal human neutrophil function and in the setting of CGD. The phagocyte oxidase complex employs a heterodimeric transmembrane protein composed of gp91phox and p22phox to relay electrons from NADPH to molecular oxygen, while other cofactors contribute to localization and regulation of the activity of the assembled oxidase. The b-type cytochrome gp91phox, also known as NOX2, serves as the catalytic component of this multicomponent enzyme complex. Although many of the features of the composition and regulation of the phagocyte oxidase may apply as well to NOX2 expressed in non-phagocytes and to other members of the NOX protein family, exceptions exist and pose special challenges to investigators exploring the biology of NADPH oxidases.

Enhanced Immunoaffinity Purification of Human Neutrophil Flavocytochrome B for Structure Determination by Electron Microscopy

Determination of the structure of human neutrophil (PMN) flavocytochrome b (Cytb) is a necessary step for the understanding of the structure-function essentials of NADPH oxidase activity. This understanding is crucial for structure-driven therapeutic approaches addressing control of inflammation and infection. Our work on purification and sample preparation of Cytb has facilitated progress toward the goal of structure determination. Here we describe exploiting immunoaffinity purification of Cytb for initial examination of its size and shape by a combination of classical and cryoelectron microscopic (EM) methods. For these evaluations, we used conventional negative-stain transmission electron microscopy (TEM) to examine both detergent-solubilized Cytb as single particles and Cytb in phosphatidylcholine reconstituted membrane vesicles as densely packed random, partially ordered, and subcrystalline arrays. In preliminary trials, we also examined single particles by cryoelectron microscopy (cryoEM) methods. We conclude that Cytb in detergent and reconstituted in membrane is a relatively compact, symmetrical protein of about 100 Å in maximum dimension. The negative stain, preliminary cryoEM, and crude molecular models suggest that the protein is probably a heterotetramer of two p22^phox and gp91^phox subunits in both detergent micelles and membrane vesicles. This exploratory study also suggests that high-resolution 2D electron microscopic approaches may be accessible to human material collected from single donors.

Serendipitous crystallization and structure determination of bacterioferritin from Achromobacter

Bacterioferritins (Bfrs) are ferritin-like molecules with a hollow spherical 24-mer complex design that are unique to bacterial and archaeal species. They play a critical role in storing iron(III) within the complex at concentrations much higher than the feasible solubility limits of iron(III), thus maintaining iron homeostasis within cells. Here, the crystal structure of bacterioferritin from Achromobacter (Ach Bfr) that crystallized serendipitously during a crystallization attempt of an unrelated mycobacterial protein is reported at 1.95 Å resolution. Notably, Fe atoms were bound to the structure along with a porphyrin ring sandwiched between the subunits of a dimer. Furthermore, the dinuclear ferroxidase center of Ach Bfr has only a single iron bound, in contrast to the two Fe atoms in other Bfrs. The structure of Ach Bfr clearly demonstrates the substitution of a glutamate residue, which is involved in the interaction with the second Fe atom, by a threonine and the consequent absence of another Fe atom there. The iron at the dinuclear center has a tetravalent coordination, while a second iron with a hexavalent coordination was found within the porphyrin ring, generating a heme moiety. Achromobacter spp. are known opportunistic pathogens; this structure enhances the current understanding of their iron metabolism and regulation, and importantly will be useful in the design of small-molecule inhibitors against this protein through a structure-guided approach.

Interaction between p22phox and Nox4 in the endoplasmic reticulum suggests a unique mechanism of NADPH oxidase complex formation

The p22^phox protein is an essential component of the phagocytic- and inner ear NADPH oxidases but its relationship to other Nox proteins is less clear. We have studied the role of p22^phox in the TGF-β1-stimulated H₂O₂ production of primary human and murine fibroblasts. TGF-β1 induced H₂O₂ release of the examined cells, and the response was dependent on the expression of both Nox4 and p22^phox. Interestingly, the p22^phox protein was present in the absence of any detectable Nox/Duox expression, and the p22^phox level was unaffected by TGF-β1. On the other hand, Nox4 expression was dependent on the presence of p22^phox, establishing an asymmetrical relationship between the two proteins. Nox4 and p22^phox proteins localized to the endoplasmic reticulum and their distribution was unaffected by TGF-β1. We used a chemically induced protein dimerization method to study the orientation of p22^phox and Nox4 in the endoplasmic reticulum membrane. This technique is based on the rapamycin-mediated heterodimerization of the mammalian FRB domain with the FK506 binding protein. The results of these experiments suggest that the enzyme complex produces H₂O₂ into the lumen of the endoplasmic reticulum, indicating that Nox4 contributes to the development of the oxidative milieu within this organelle.

The radical SAM protein HemW is a heme chaperone

Radical S-adenosylmethionine (SAM) enzymes exist in organisms from all kingdoms of life, and all of these proteins generate an adenosyl radical via the homolytic cleavage of the S-C(5') bond of SAM. Of particular interest are radical SAM enzymes, such as heme chaperones, that insert heme into respiratory enzymes. For example, heme chaperones insert heme into target proteins but have been studied only for the formation of cytochrome c-type hemoproteins. Here, we report that a radical SAM protein, the heme chaperone HemW from bacteria, is required for the insertion of heme b into respiratory chain enzymes. As other radical SAM proteins, HemW contains three cysteines and one SAM coordinating an [4Fe-4S] cluster, and we observed one heme per subunit of HemW. We found that an intact iron-sulfur cluster was required for HemW dimerization and HemW-catalyzed heme transfer but not for stable heme binding. A bacterial two-hybrid system screen identified bacterioferritins and the heme-containing subunit NarI of the respiratory nitrate reductase NarGHI as proteins that interact with HemW. We also noted that the bacterioferritins potentially serve as heme donors for HemW. Of note, heme that was covalently bound to HemW was actively transferred to a heme-depleted, catalytically inactive nitrate reductase, restoring its nitrate-reducing enzyme activity. Finally, the human HemW orthologue radical SAM domain-containing 1 (RSAD1) stably bound heme. In conclusion, our findings indicate that the radical SAM protein family HemW/RSAD1 is a heme chaperone catalyzing the insertion of heme into hemoproteins.

Resequencing of a mutant bearing an iron starvation recovery phenotype defines Slr1658 as a new player in the regulatory network of a model cyanobacterium

Photosynthetic microorganisms encounter an erratic nutrient environment characterized by periods of iron limitation and sufficiency. Surviving in such an environment requires mechanisms for handling these transitions. Our study identified a regulatory system involved in the process of recovery from iron limitation in cyanobacteria. We set out to study the role of bacterioferritin co-migratory proteins during transitions in iron bioavailability in the cyanobacterium Synechocystis sp. PCC 6803 using knockout strains coupled with physiological and biochemical measurements. One of the mutants displayed slow recovery from iron limitation. However, we discovered that the cause of the phenotype was not the intended knockout but rather the serendipitous selection of a mutation in an unrelated locus, slr1658. Bioinformatics analysis suggested similarities to two-component systems and a possible regulatory role. Transcriptomic analysis of the recovery from iron limitation showed that the slr1658 mutation had an extensive effect on the expression of genes encoding regulatory proteins, proteins involved in the remodeling and degradation of the photosynthetic apparatus and proteins modulating electron transport. Most significantly, expression of the cyanobacterial homologue of the cyclic electron transport protein PGR5 was upregulated 1000-fold in slr1658 disruption mutants. pgr5 transcripts in the Δslr1658 mutant retained these high levels under a range of stress and recovery conditions. The results suggest that slr1658 is part of a regulatory operon that, among other aspects, affects the regulation of alternative electron flow. Disruption of its function has deleterious results under oxidative stress promoting conditions.

Increased Expression of p22phox Mediates Airway Hyperresponsiveness in an Experimental Model of Asthma

AIM

Chronic airway diseases such as asthma are associated with increased production of reactive oxygen species (ROS) and oxidative stress. Endogenous NADPH oxidases are a major source of superoxide in lung, but their underlying role in asthma pathology is poorly understood. We sought to characterize the involvement of NADPH oxidase in allergic asthma by studying the role of CYBA (p22phox) in human asthma and murine house dust mite (HDM)-induced allergic airway inflammation.

RESULTS

Increased expression and localization of p22-PHOX were observed in biopsies of asthmatic patients. HDM-treated wild-type mice possessed elevated p22phox expression, corresponding with elevated superoxide production. p22phox knockout (KO) mice did not induce superoxide and were protected against HDM-induced goblet cell hyperplasia and mucus production and HDM-induced airway hyperresponsiveness (AHR). IL-13-induced tracheal hyperreactivity and signal transducer and activator of transcription (STAT)6 phosphorylation were attenuated in the absence of p22phox or catalase pretreatment.

INNOVATION

Our study identifies increased expression of p22phox in lungs of asthmatic patients and in experimental model. The induced AHR and mucus hypersecretion are a result of increased ROS from the p22phox-dependent NADPH oxidase, which in turn activates STAT6 for the pathological feature of asthma.

CONCLUSIONS

Together with the increased p22phox expression in lungs of asthmatic patients, these findings demonstrate a crucial role of p22phox-dependent NADPH oxidase for the development of mucus hypersecretion and AHR in HDM-induced model of asthma. This suggests that inhibition of functional NADPH oxidase by selective interference of p22phox might hold a promising therapeutic strategy for the management of asthma. Antioxid. Redox Signal. 27, 1460-1472.

A simple and efficient method to prepare pure dimers and monomers of the cytochrome b 6 f complex from spinach

Using a single size-exclusion chromatography we were able to isolate highly pure dimers and monomers of the Cyt b ₆ f complex from spinach from a bulk preparation of that protein complex obtained with a standard procedure. At higher protein/detergent ratio during the chromatography most of the Cyt b ₆ f complex remained as dimers. In contrast, at lower protein/detergent ratio (around 15 times lower), most dimers became monomerized. As a bonus, this chromatography also allowed the elimination of potential Chl a contaminant to the Cyt b ₆ f preparations. SDS-PAGE protein analysis with 18% (w/v) acrylamide revealed the loss of the ISP subunit in our monomeric preparation. However, it fully retained the content of Chl a, a prerequisite to perform any spectroscopic study involving this unique pigment.

Role of the NAD(P)H quinone oxidoreductase NQR and the cytochrome b AIR12 in controlling superoxide generation at the plasma membrane

MAIN CONCLUSION

The quinone reductase NQR and the b-type cytochrome AIR12 of the plasma membrane are important for the control of reactive oxygen species in the apoplast. AIR12 and NQR are two proteins attached to the plant plasma membrane which may be important for generating and controlling levels of reactive oxygen species in the apoplast. AIR12 (Auxin Induced in Root culture) is a single gene of Arabidopsis that codes for a mono-heme cytochrome b. The NADPH quinone oxidoreductase NQR is a two-electron-transferring flavoenzyme that contributes to the generation of O 2•- in isolated plasma membranes. A. thaliana double knockout plants of both NQR and AIR12 generated more O 2•- and germinated faster than the single mutant affected in AIR12. To test whether NQR and AIR12 are able to interact functionally, recombinant purified proteins were added to plasma membranes isolated from soybean hypocotyls. In vitro NADH-dependent O 2•- production at the plasma membrane in the presence of NQR was reduced upon addition of AIR12. Electron donation from semi-reduced menadione to AIR12 was shown to take place. Biochemical analysis showed that purified plasma membrane from soybean hypocotyls or roots contained phylloquinone and menaquinone-4 as redox carriers. This is the first report on the occurrence of menaquinone-4 in eukaryotic photosynthetic organisms. We propose that NQR and AIR12 interact via the quinone, allowing an electron transfer from cytosolic NAD(P)H to apoplastic monodehydroascorbate and control thereby the level of reactive oxygen production and the redox state of the apoplast.

An Organelle RNA Recognition Motif Protein Is Required for Photosystem II Subunit psbF Transcript Editing

Loss-of-function mutations in ORGANELLE RNA RECOGNITION MOTIF PROTEIN6 (ORRM6) result in the near absence of RNA editing of psbF-C77 and the reduction in accD-C794 editing in Arabidopsis (Arabidopsis thaliana). The orrm6 mutants have decreased levels of photosystem II (PSII) proteins, especially PsbF, lower PSII activity, pale green pigmentation, smaller leaf and plant sizes, and retarded growth. Stable expression of ORRM6 rescues the orrm6 editing defects and mutant phenotype. Unlike ORRM1, the other known ORRM plastid editing factor, ORRM6, does not contain RNA editing interacting protein/multiple organellar RNA editing factor (RIP/MORF) boxes, which are required for ORRM1 to interact with site-specific pentatricopeptide repeat protein editing factors. ORRM6 interacts with RIP1/MORF8, RIP2/MORF2, and RIP9/MORF9, known components of RNA editosomes. While some plastid RRM proteins are involved in other forms of RNA processing and translation, the primary function of ORRM6 is evidently to mediate psbF-C77 editing, like the essential site-specific pentatricopeptide repeat protein LOW PSII ACCUMULATION66. Stable expression in the orrm6 mutants of a nucleus-encoded, plastid-targeted PsbF protein from a psbF gene carrying a T at nucleotide 77 significantly increases leaf and plant sizes, chlorophyll content, and PSII activity. These transformants demonstrate that plastid RNA editing can be bypassed through the expression of nucleus-encoded, edited forms of plastid genes.

Differential Roles of Iron Storage Proteins in Maintaining the Iron Homeostasis in Mycobacterium tuberculosis

Ferritins and bacterioferritins are iron storage proteins that represent key players in iron homeostasis. Several organisms possess both forms of ferritins, however, their relative physiological roles are less understood. Mycobacterium tuberculosis possesses both ferritin (BfrB) and bacterioferritin (BfrA), playing an essential role in its pathogenesis as reported by us earlier. This study provides insights into the role of these two proteins in iron homeostasis by employing M. tuberculosis bfr mutants. Our data suggests that BfrA is required for efficient utilization of stored iron under low iron conditions while BfrB plays a crucial role as the major defense protein under excessive iron conditions. We show that these two proteins provide protection against oxidative stress and hypoxia. Iron incorporation study showed that BfrB has higher capacity for storing iron than BfrA, which augurs well for efficient iron quenching under iron excess conditions. Moreover, iron release assay demonstrated that BfrA has 3 times superior ability to release stored iron emphasizing its requirement for efficient iron release under low iron conditions, facilitated by the presence of heme. Thus, for the first time, our observations suggest that the importance of BfrA or BfrB separately might vary depending upon the iron situation faced by the cell.

miRNA-216 and miRNA-499 target cyb561d2 in zebrafish in response to fipronil exposure

MicroRNA (miRNA) can regulate the expression of its target gene by mediating mRNA cleavage or by translational repression at a post-transcriptional level. Usually, one miRNA may regulate many genes as its targets, while one gene may also be targeted by many miRNAs. We previously demonstrated that cyb561d2, whose protein product is involved in cell defense, and chemical stress, is targeted by miR-155 in adult zebrafish (Danio rerio) when exposed to fipronil (5-amino-1-[2,6-dichloro-4-(trifluoromethyl) phenyl]-4-[(trifluoromethyl) sulphinyl]-1H-pyrazole-3-carbonitrile). Microcosm Targets prediction showed that the cyb561d2 gene is also highly possibly targeted by miR-194a, miR-216b, miR-429, and miR-499. These interactions need to be further validated experimentally. In this study, we evaluated the effects of fipronil on miR-194a, miR-216b, miR-429, miR-499 and cyb561d2 in zebrafish and investigated whether these four miRNAs could regulate the expression of cyb561d2 in both mRNA and protein levels. The expression of cyb561d2 was upregulated in both mRNA and protein level in a dose-dependent manner upon stimulation of fipronil, and miR-216b and miR-499 were downregulated concurrently, whereas there was no significant changes were observed in the expression level of miR-194a and miR-429. The dual luciferase report assay demonstrated that miR-216b and miR-499 interacted with cyb561d2 3'-untranslated regions (3'-UTR), miR-194a and miR-429 did not stimulate degradation of cyb561d2 mRNA. The expression of cyb561d2 was reduced in both mRNA and protein level when ZF4 cells were transfected with miR-499 mimic, whereas expression level of both mRNA and protein was increased when endogenous miR-499 was inhibited by transfection with miR-499 inhibitor. Likewise, the mRNA and protein level of cyb561d2 was affected by treatment with the mimics and the inhibitor of miR-216b. In contrast, when ZF4 cells were transfected with a mimic of miR-194a or miR-429, the expression of cyb561d2 mRNA was not significantly changed. As a result, cyb561d2 is targeted by miR-155, miR-216b and miR-499 upon fipronil exposure, and miR-194a and miR-429 can not target cyb561d2. The expression pattern of these 3 miRNAs presents novel fipronil responses that could be used as a toxicological biomarker.

Fermented Goat's Milk Consumption Improves Duodenal Expression of Iron Homeostasis Genes during Anemia Recovery

Despite the crucial roles of duodenal cytochrome b (Dcytb), divalent metal transporter 1 (DMT1), ferritin light chain (Ftl1), ferroportin 1 (FPN1), transferrin receptor 1 (TfR1), and hepcidin antimicrobial peptide (Hamp) in Fe metabolism, no studies have investigated the modulations of these genes during Fe repletion with fermented milks. Analysis included Fe status markers and gene and protein expression in enterocytes of control and anemic animals fed fermented milks. Fermented goat's milk up-regulated enterocyte Dcytb, DMT1, FPN1, and Ftl1 and down-regulated TfR1 and Hamp gene expression in control and anemic animals. Anemia decreased Dcytb, DMT1, and Ftl1 in animals fed fermented cow's milk and up-regulated TfR1 and Hamp expression. Fe overload down-regulated Dcytb and TfR1 in animals fed fermented cow's milk and up-regulated DMT1 and FPN1 gene expression. Fermented goat's milk increased expression of duodenal Dcytb, DMT1, and FPN1 and decreased Hamp and TfR1, improving Fe metabolism during anemia recovery.

Three Aromatic Residues are Required for Electron Transfer during Iron Mineralization in Bacterioferritin

Ferritins are iron storage proteins that overcome the problems of toxicity and poor bioavailability of iron by catalyzing iron oxidation and mineralization through the activity of a diiron ferroxidase site. Unlike in other ferritins, the oxidized di-Fe(3+) site of Escherichia coli bacterioferritin (EcBFR) is stable and therefore does not function as a conduit for the transfer of Fe(3+) into the storage cavity, but instead acts as a true catalytic cofactor that cycles its oxidation state while driving Fe(2+) oxidation in the cavity. Herein, we demonstrate that EcBFR mineralization depends on three aromatic residues near the diiron site, Tyr25, Tyr58, and Trp133, and that a transient radical is formed on Tyr25. The data indicate that the aromatic residues, together with a previously identified inner surface iron site, promote mineralization by ensuring the simultaneous delivery of two electrons, derived from Fe(2+) oxidation in the BFR cavity, to the di-ferric catalytic site for safe reduction of O2.

Direct Recording of Trans-Plasma Membrane Electron Currents Mediated by a Member of the Cytochrome b561 Family of Soybean

Trans-plasma membrane electron transfer is achieved by b-type cytochromes of different families, and plays a fundamental role in diverse cellular processes involving two interacting redox couples that are physically separated by a phospholipid bilayer, such as iron uptake and redox signaling. Despite their importance, no direct recordings of trans-plasma membrane electron currents have been described in plants. In this work, we provide robust electrophysiological evidence of trans-plasma membrane electron flow mediated by a soybean (Glycine max) cytochrome b561 associated with a dopamine β-monooxygenase redox domain (CYBDOM), which localizes to the plasma membrane in transgenic Arabidopsis (Arabidopsis thaliana) plants and CYBDOM complementary RNA-injected Xenopus laevis oocytes. In oocytes, two-electrode voltage clamp experiments showed that CYBDOM-mediated currents were activated by extracellular electron acceptors in a concentration- and type-specific manner. Current amplitudes were voltage dependent, strongly potentiated in oocytes preinjected with ascorbate (the canonical electron donor for cytochrome b561), and abolished by mutating a highly conserved His residue (H292L) predicted to coordinate the cytoplasmic heme b group. We believe that this unique approach opens new perspectives in plant transmembrane electron transport and beyond.

Studies of Cream Seeded Carioca Beans (Phaseolus vulgaris L.) from a Rwandan Efficacy Trial: In Vitro and In Vivo Screening Tools Reflect Human Studies and Predict Beneficial Results from Iron Biofortified Beans

Iron (Fe) deficiency is a highly prevalent micronutrient insufficiency predominantly caused by a lack of bioavailable Fe from the diet. The consumption of beans as a major food crop in some populations suffering from Fe deficiency is relatively high. Therefore, our objective was to determine whether a biofortified variety of cream seeded carioca bean (Phaseolus vulgaris L.) could provide more bioavailable-Fe than a standard variety using in-vivo (broiler chicken, Gallus gallus) and in-vitro (Caco-2 cell) models. Studies were conducted under conditions designed to mimic the actual human feeding protocol. Two carioca-beans, a standard (G4825; 58 μg Fe/g) and a biofortified (SMC; 106 μg Fe/g), were utilized. Diets were formulated to meet the nutrient requirements of Gallus gallus except for Fe (33.7 and 48.7 μg Fe/g, standard and biofortified diets, respectively). In-vitro observations indicated that more bioavailable-Fe was present in the biofortified beans and diet (P<0.05). In-vivo, improvements in Fe-status were observed in the biofortified bean treatment, as indicated by the increased total-body-Hemoglobin-Fe, and hepatic Fe-concentration (P<0.05). Also, DMT-1 mRNA-expression was increased in the standard bean treatment (P<0.05), indicating an upregulation of absorption to compensate for less bioavailable-Fe. These results demonstrate that the biofortified beans provided more bioavailable Fe; however, the in vitro results revealed that ferritin formation values were relatively low. Such observations are indicative of the presence of high levels of polyphenols and phytate that inhibit Fe absorption. Indeed, we identified higher levels of phytate and quercetin 3-glucoside in the Fe biofortified bean variety. Our results indicate that the biofortified bean line was able to moderately improve Fe-status, and that concurrent increase in the concentration of phytate and polyphenols in beans may limit the benefit of increased Fe-concentration. Therefore, specific targeting of such compounds during the breeding process may yield improved dietary Fe-bioavailability. Our findings are in agreement with the human efficacy trial that demonstrated that the biofortified carioca beans improved the Fe-status of Rwandan women. We suggest the utilization of these in vitro and in vivo screening tools to guide studies aimed to develop and evaluate biofortified staple food crops. This approach has the potential to more effectively utilize research funds and provides a means to monitor the nutritional quality of the Fe-biofortified crops once released to farmers.

Distinct Regulation of Transmitter Release at the Drosophila NMJ by Different Isoforms of nemy

Synaptic transmission is highly plastic and subject to regulation by a wide variety of neuromodulators and neuropeptides. In the present study, we have examined the role of isoforms of the cytochrome b561 homologue called no extended memory (nemy) in regulation of synaptic strength and plasticity at the neuromuscular junction (NMJ) of third instar larvae in Drosophila. Specifically, we generated two independent excisions of nemy that differentially affect the expression of nemy isoforms. We show that the nemy45 excision, which specifically reduces the expression of the longest splice form of nemy, leads to an increase in stimulus evoked transmitter release and altered synaptic plasticity at the NMJ. Conversely, the nemy26.2 excision, which appears to reduce the expression of all splice forms except the longest splice isoform, shows a reduction in stimulus evoked transmitter release, and enhanced synaptic plasticity. We further show that nemy45 mutants have reduced levels of amidated peptides similar to that observed in peptidyl-glycine hydryoxylating mono-oxygenase (PHM) mutants. In contrast, nemy26.2 mutants show no defects in peptide amidation but rather display a decrease in Tyramine β hydroxylase activity (TβH). Taken together, these results show non-redundant roles for the different nemy isoforms and shed light on the complex regulation of neuromodulators.

NADPH Oxidase-Dependent NLRP3 Inflammasome Activation and its Important Role in Lung Fibrosis by Multiwalled Carbon Nanotubes

The purpose of this paper is to elucidate the key role of NADPH oxidase in NLRP3 inflammasome activation and generation of pulmonary fibrosis by multi-walled carbon nanotubes (MWCNTs). Although it is known that oxidative stress plays a role in pulmonary fibrosis by single-walled CNTs, the role of specific sources of reactive oxygen species, including NADPH oxidase, in inflammasome activation remains to be clarified. In this study, three long aspect ratio (LAR) materials (MWCNTs, single-walled carbon nanotubes, and silver nanowires) are used to compare with spherical carbon black and silver nanoparticles for their ability to trigger oxygen burst activity and NLRP3 assembly. All LAR materials but not spherical nanoparticles induce robust NADPH oxidase activation and respiratory burst activity in THP-1 cells, which are blunted in p22(phox) -deficient cells. The NADPH oxidase is directly involved in lysosomal damage by LAR materials, as demonstrated by decreased cathepsin B release and IL-1β production in p22(phox) -deficient cells. Reduced respiratory burst activity and inflammasome activation are also observed in bone marrow-derived macrophages from p47(phox) -deficient mice. Moreover, p47(phox) -deficient mice have reduced IL-1β production and lung collagen deposition in response to MWCNTs. Lung fibrosis is also suppressed by N-acetyl-cysteine in wild-type animals exposed to MWCNTs.

Computational modeling analysis of mitochondrial superoxide production under varying substrate conditions and upon inhibition of different segments of the electron transport chain

A computational mechanistic model of superoxide (O2•-) formation in the mitochondrial electron transport chain (ETC) was developed to facilitate the quantitative analysis of factors controlling mitochondrial O2•- production and assist in the interpretation of experimental studies. The model takes into account all individual electron transfer reactions in Complexes I and III. The model accounts for multiple, often seemingly contradictory observations on the effects of ΔΨ and ΔpH, and for the effects of multiple substrate and inhibitor conditions, including differential effects of Complex III inhibitors antimycin A, myxothiazol and stigmatellin. Simulation results confirm that, in addition to O2•- formation in Complex III and at the flavin site of Complex I, the quinone binding site of Complex I is an additional superoxide generating site that accounts for experimental observations on O2•- production during reverse electron transfer. However, our simulation results predict that, when cytochrome c oxidase is inhibited during oxidation of succinate, ROS production at this site is eliminated and almost all superoxide in Complex I is generated by reduced FMN, even when the redox pressure for reverse electron transfer from succinate is strong. In addition, the model indicates that conflicting literature data on the kinetics of electron transfer in Complex III involving the iron-sulfur protein-cytochrome bL complex can be resolved in favor of a dissociation of the protein only after electron transfer to cytochrome bH. The model predictions can be helpful in understanding factors driving mitochondrial superoxide formation in intact cells and tissues.

AIR12, a b-type cytochrome of the plasma membrane of Arabidopsis thaliana is a negative regulator of resistance against Botrytis cinerea

AIR12 (Auxin Induced in Root culture) is a single gene of Arabidopsis that codes for a mono-heme cytochrome b. Recombinant AIR12 from Arabidopsis accepted electrons from ascorbate or superoxide, and donated electrons to either monodehydroascorbate or oxygen. AIR12 was found associated in vivo to the plasma membrane. Though linked to the membrane by a glycophosphatidylinositol anchor, AIR12 is a hydrophilic and glycosylated protein predicted to be fully exposed to the apoplast. The expression pattern of AIR12 in Arabidopsis is developmentally regulated and correlated to sites of controlled cell separation (e.g. micropilar endosperm during germination, epidermal cells surrounding the emerging lateral root) and cells around wounds. Arabidopsis (Landsberg erecta-0) mutants with altered levels of AIR12 did not show any obvious phenotype. However, AIR12-overexpressing plants accumulated ROS (superoxide, hydrogen peroxide) and lipid peroxides in leaves, indicating that AIR12 may alter the redox state of the apoplast under particular conditions. On the other hand, AIR12-knock out plants displayed a strongly decreased susceptibility to Botrytis cinerea infection, which in turn induced AIR12 expression in susceptible wild type plants. Altogether, the results suggest that AIR12 plays a role in the regulation of the apoplastic redox state and in the response to necrotrophic pathogens. Possible relationships between these functions are discussed.

Role of duodenal iron transporters and hepcidin in patients with alcoholic liver disease

Patients with alcoholic liver disease (ALD) often display disturbed iron indices. Hepcidin, a key regulator of iron metabolism, has been shown to be down-regulated by alcohol in cell lines and animal models. This down-regulation led to increased duodenal iron transport and absorption in animals. In this study, we investigated gene expression of duodenal iron transport molecules and hepcidin in three groups of patients with ALD (with anaemia, with iron overload and without iron overload) and controls. Expression of DMT1, FPN1, DCYTB, HEPH, HFE and TFR1 was measured in duodenal biopsies by using real-time PCR and Western blot. Serum hepcidin levels were measured by using ELISA. Serum hepcidin was decreased in patients with ALD. At the mRNA level, expressions of DMT1, FPN1 and TFR1 genes were significantly increased in ALD. This pattern was even more pronounced in the subgroups of patients without iron overload and with anaemia. Protein expression of FPN1 paralleled the increase at the mRNA level in the group of patients with ALD. Serum ferritin was negatively correlated with DMT1 mRNA. The down-regulation of hepcidin expression leading to up-regulation of iron transporters expression in the duodenum seems to explain iron metabolism disturbances in ALD. Alcohol consumption very probably causes suppression of hepcidin expression in patients with ALD.

Photo-oxidation of tyrosine in a bio-engineered bacterioferritin 'reaction centre'-a protein model for artificial photosynthesis

The photosynthetic reaction centre (RC) is central to the conversion of solar energy into chemical energy and is a model for bio-mimetic engineering approaches to this end. We describe bio-engineering of a Photosystem II (PSII) RC inspired peptide model, building on our earlier studies. A non-photosynthetic haem containing bacterioferritin (BFR) from Escherichia coli that expresses as a homodimer was used as a protein scaffold, incorporating redox-active cofactors mimicking those of PSII. Desirable properties include: a di-nuclear metal binding site which provides ligands for bivalent metals, a hydrophobic pocket at the dimer interface which can bind a photosensitive porphyrin and presence of tyrosine residues proximal to the bound cofactors, which can be utilised as efficient electron-tunnelling intermediates. Light-induced electron transfer from proximal tyrosine residues to the photo-oxidised ZnCe6(•+), in the modified BFR reconstituted with both ZnCe6 and Mn(II), is presented. Three site-specific tyrosine variants (Y25F, Y58F and Y45F) were made to localise the redox-active tyrosine in the engineered system. The results indicate that: presence of bound Mn(II) is necessary to observe tyrosine oxidation in all BFR variants; Y45 the most important tyrosine as an immediate electron donor to the oxidised ZnCe6(•+) and that Y25 and Y58 are both redox-active in this system, but appear to function interchangebaly. High-resolution (2.1Å) crystal structures of the tyrosine variants show that there are no mutation-induced effects on the overall 3-D structure of the protein. Small effects are observed in the Y45F variant. Here, the BFR-RC represents a protein model for artificial photosynthesis.

Sex differences in iron status and hepcidin expression in rats

Studies have shown that men and women exhibit significant differences regarding iron status. However, the effects of sex on iron accumulation and distribution are not well established. In this study, female and male Sprague-Dawley rats were killed at 4 months of age. Blood samples were analyzed to determine the red blood cell (RBC) count, hemoglobin (Hb) concentration, hematocrit (Hct), and mean red blood cell volume (MCV). The serum samples were analyzed to determine the concentrations of serum iron (SI), transferrin saturation (TS), ferritin, soluble transferrin receptor (sTfR), and erythropoietin (EPO). The tissue nonheme iron concentrations were measured in the liver, spleen, bone marrow, kidney, heart, gastrocnemius, duodenal epithelium, lung, pallium, cerebellum, hippocampus, and striatum. Hepatic hepcidin expression was detected by real-time PCR analysis. The synthesis of ferroportin 1 (FPN1) in the liver, spleen, kidney, and bone marrow was determined by Western blot analysis. The synthesis of duodenal cytochrome B561 (DcytB), divalent metal transporter 1 (DMT1), FPN1, hephaestin (HP) in the duodenal epithelium was also measured by Western blot analysis. The results showed that the RBC, Hb, and Hct in male rats were higher than those in female rats. The SI and plasma TS levels were lower in male rats than in female rats. The levels of serum ferritin and sTfR were higher in male rats than in female rats. The EPO levels in male rats were lower than that in female rats. The nonheme iron contents in the liver, spleen, bone marrow, and kidney in male rats were also lower (56.7, 73.2, 60.6, and 61.4 % of female rats, respectively). Nonheme iron concentrations in the heart, gastrocnemius, duodenal epithelium, lung, and brain were similar in rats of both sexes. A moderate decrease in hepatic hepcidin mRNA content was also observed in male rats (to 56.0 % of female rats). The levels of FPN1 protein in the liver, spleen, and kidney were higher in male rats than in female rats. There was no significant change in FPN1 expression in bone marrow. Significant difference was also not found in DcytB, DMT1, FPN1, and HP protein levels in the duodenal epithelium between male and female rats. These data suggest that iron is distributed differently in male and female rats. This difference in iron distribution may be associated with the difference in the hepcidin level.

Investigating the photoprotective role of cytochrome b-559 in photosystem II in a mutant with altered ligation of the haem

Despite many years of study, the physiological role of cytochrome b-559 (Cyt b-559) within the photosystem II (PSII) complex still remains unclear. Here we describe the analysis of a mutant of the green alga Chlamydomonas reinhardtii in which the His ligand to the haem, provided by the alpha subunit, has been replaced by a Cys residue. The mutant is unable to grow photoautotrophically but can assemble oxygen-evolving PSII supercomplexes to 15-20% of the levels found in the wild-type control. Haem is still detected in the isolated PSII supercomplexes but at sub-stoichiometric levels consistent with weaker binding to the mutated cytochrome. Analysis of PSII activity in cells indicates slowed electron transfer in the mutant between plastoquinones QA and QB. We show that PSII activity in the mutant is more sensitive to chronic photoinhibition than the WT control because of two effects: a faster rate of damage and an impaired PSII repair cycle at the level of synthesis and/or incorporation of D1 into PSII. We also demonstrate that Cyt b-559 plays a role during the critical stage of assembling the Mn4CaO5 cluster. Overall we conclude that Cyt b-559 optimises electron transfer on the acceptor side of PSII and plays physiologically important roles in the assembly, repair and maintenance of the complex.

Role of vascular oxidative stress in obesity and metabolic syndrome

Obesity is associated with vascular diseases that are often attributed to vascular oxidative stress. We tested the hypothesis that vascular oxidative stress could induce obesity. We previously developed mice that overexpress p22phox in vascular smooth muscle, tg(sm/p22phox), which have increased vascular ROS production. At baseline, tg(sm/p22phox) mice have a modest increase in body weight. With high-fat feeding, tg(sm/p22phox) mice developed exaggerated obesity and increased fat mass. Body weight increased from 32.16 ± 2.34 g to 43.03 ± 1.44 g in tg(sm/p22phox) mice (vs. 30.81 ± 0.71 g to 37.89 ± 1.16 g in the WT mice). This was associated with development of glucose intolerance, reduced HDL cholesterol, and increased levels of leptin and MCP-1. Tg(sm/p22phox) mice displayed impaired spontaneous activity and increased mitochondrial ROS production and mitochondrial dysfunction in skeletal muscle. In mice with vascular smooth muscle-targeted deletion of p22phox (p22phox(loxp/loxp)/tg(smmhc/cre) mice), high-fat feeding did not induce weight gain or leptin resistance. These mice also had reduced T-cell infiltration of perivascular fat. In conclusion, these data indicate that vascular oxidative stress induces obesity and metabolic syndrome, accompanied by and likely due to exercise intolerance, vascular inflammation, and augmented adipogenesis. These data indicate that vascular ROS may play a causal role in the development of obesity and metabolic syndrome.