Ahp deficiency-induced redox imbalance leads to metabolic alterations in E.coli

Alkyl hydroperoxide reductase (Ahp) is the primary scavenger of endogenous hydrogen peroxide in Escherichia coli (E. coli). Ahp-deficient strains have been found to have high reactive oxygen species (ROS) levels, sufficient to cause cell damage. However, the exact role and underlying mechanisms of Ahp deficiency-induced cell damage remain largely unknown. Here, the E. coli MG1655 ΔAhp mutant strain was constructed as a model of deficiency to assess its role. The cells of the ΔAhp strain were found to be significantly longer than those of the wild strain, with elevated ROS and hydrogen peroxide (H2O2) levels. Proteome, redox proteome and metabolome analyses were performed to systematically present a global and quantitative profile and delineate the redox signaling and metabolic alterations at the proteome, metabolome, and cysteine oxidation site levels. The multiomics data revealed that Ahp deficiency disrupted the redox balance, activated the OxyR system, upregulated oxidative defense proteins and inhibited the TCA cycle to some extent. Surprisingly, the mutant strain shifted from aerobic respiration to anaerobic respiration and fermentation during the logarithmic phase in the presence of sufficient O2. The acid resistance system was activated to mitigate the effect of excessive acid produced by fermentation. Taken together, the results of this study demonstrated that Ahp deficiency triggered cellular redox imbalance and regulated metabolic pathways to confer resistance to submicromolar intracellular H2O2 levels in E. coli.

Characterization of oxidative stress-induced cgahp, a gene coding for alkyl hydroperoxide reductase, from industrial importance Corynebacterium glutamicum

Alkyl hydroperoxide reductase (Ahp), comprised of four different subunits AhpC, AhpD, AhpE, and AhpF, is a thiol-based antioxidative enzyme with the ability to protect bacteria against oxidative stress. Functionally, AhpC and AhpE considered as peroxidases directly detoxify peroxides, while AhpD and AhpF as oxidoreductases restore oxidized peroxidases to their reduced form. Corynebacterium glutamicum ncgl0877 encodes a putative Ahp with a unique Cys-Pro-Phe-Cys (C-P-G-C) active-site motif, similar with those of the thiol-disulfide oxidoreductases such as thioredoxin (Trx), mycoredoxin-1 (Mrx1) and AhpD. However, its physiological and biochemical functions remain unknown in C. glutamicum. Here, we report that NCgl0877, designated CgAhp, is involved in the protection against organic peroxide (OP) stress. The cgahp-deleted strain is notably more sensitive to OP stress. The cgahp expression is controlled by a MarR-type transcriptional repressor OasR (organic peroxide- and antibiotic-sensing regulator). The physiological role of CgAhp in resistance to OP stresses is corroborated by its induced expression under stresses. Although CgAhp has a weak peroxidase activity toward OP, it mainly supports the OP-scavenging activity of the thiol-dependent peroxidase preferentially linked to the dihydrolipoamide dehydrogenase (Lpd)/dihydrolipoamide succinyltransferase (SucB)/NADH system. The C-P-G-C motif of CgAhp is essential to maintain the reductase activity. In conclusion, our study identifies CgAhp, behaving like AhpD, as a key disulfide oxidoreductase involved in the oxidative stress tolerance and the functional electron donor for peroxidase.

Crystal structure of the AhpD-like protein DR1765 from Deinococcus radiodurans R1

Deinococcus radiodurans is well known for its extreme resistance to ionizing radiation (IR). Since reactive oxygen species generated by IR can damage various cellular components, D. radiodurans has developed effective antioxidant systems to cope with this oxidative stress. dr1765 from D. radiodurans is predicted to encode an alkyl hydroperoxidase-like protein (AhpD family), which is implicated in the reduction of hydrogen peroxide (H₂O₂) and organic hydroperoxides. In this study, we constructed a dr1765 mutant strain (Δdr1765) and examined the survival rate after H₂O₂ treatment. Δdr1765 showed a significant decrease in the H₂O₂ resistance compared to the wild-type strain. We also determined the crystal structure of DR1765 at 2.27 Å resolution. DR1765 adopted an all alpha helix protein fold representative of the AhpD-like superfamily. Structural comparisons of DR1765 with its structural homologues revealed that DR1765 possesses the Glu74-Cys86-Tyr88-Cys89-His93 signature motif, which is conserved in the proton relay system of AhpD. Complementation of Δdr1765 with dr1765 encoding C86A or C89A mutation failed to restore the survival rate to wild-type level. Taken together, these results suggest that DR1765 might function as an AhpD to protect cells from oxidative stress.

Crystal structure of sulfonic peroxiredoxin Ahp1 in complex with thioredoxin Trx2 mimics a conformational intermediate during the catalytic cycle

Peroxiredoxin (Prx) is a thiol-based peroxidase that eliminates reactive oxygen species to avoid oxidative damage. Alkyl hydroperoxide reductase Ahp1 is a novel and specific typical 2-cysteine Prx. Here, we present the crystal structure of sulfonic Ahp1 complexed with thioredoxin Trx2 at 2.12 Å resolution. This structure implies that the transient Ahp1-Trx2 complex during the catalytic cycle already have an ability to decompose the peroxides. Structural analysis reveals that the segment glutamine23-lysine32 juxtaposed to the resolving cysteine (C_R) of Ahp1 moves inward to generate a compact structure upon peroxidatic cysteine (C_P) overoxidation, resulting in the breakdown of several conserved hydrogen bonds formed by Ahp1-Trx2 complex interaction. Structural comparisons suggest that the structure of sulfonic Ahp1 represents a novel conformation of Ahp1, which can mimic a conformational intermediate between the reduced and oxidized forms. Therefore, this study may provide a new structural insight into the intermediate state in which the segment glutamine23-lysine32 juxtaposed to the cysteine31 (C_R) undergoes a conformational change upon cysteine62 (C_P) oxidation to prepare for the formation of an intermolecular C_P-C_R disulfide bond during Ahp1 catalytic cycle.

Evaluations of Alkyl hydroperoxide reductase B cell antigen epitope as a potential epitope vaccine against Campylobacter jejuni

Objective

The present study aimed to screen and find alkyl hydroperoxide reductase (AhpC) B cell dominant epitope of Campylobacter jejuni (C. jejuni).

Materials and methods

Bio-informatic algorithms were used to predict B cell epitopes of AhpC. The AhpC protein and chemically synthesized antigenic epitopes of C. jejuni were considered as antigens, and the AhpC antibody was used as the primary antibody, ELISA and dot blot were used to analyze and screen the dominant epitope. The specific IgG of mice serum and IL-4 in splenocyte culture supernatant were detected by ELISA. The protective efficacy was evaluated by animal disease index and tissue histopathological staining of the jejunum.

Results

Seven epitopes of AhpC were predicted, one epitope (AhpC_4–16) was found to recognize the antibodies of AhpC and had strong antigenicity by ELISA and dot blot analysis. In epitope AhpC_4–16 immunized mice, specific IgG of serum and IL-4 in splenocyte culture supernatant were significantly higher. The illness index decreased significantly, the protective rate was 66.67%. Histopathology displayed that the jejunum morphology was better than the control group.

Conclusions

These findings suggested that epitope AhpC_4–16 showed effective protective role against C. jejuni and is a candidate epitope of vaccine against this pathogen.

Purified thioredoxin reductase from O2-sensitive Bifidobacterium bifidum degrades H2O2 by interacting with alkyl hydroperoxide reductase

Bifidobacterium is beneficial for host health and exhibits different O₂ sensitivity levels among species or strains via unknown mechanisms. Bifidobacterium bifidum JCM1255^T, a type species of Bifidobacterium, is an O₂-sensitive bacterium that can grow under low-O₂ (5%) conditions, and the growth of this species is inhibited under high-O₂ conditions (10% ∼) with accumulation of H₂O₂. We previously reported that NADH or NAD(P)H oxidase-active fractions were detected during purification using microaerobically grown B. bifidum cells, and the active enzyme was purified from the NADH oxidase-active fraction. The purified enzyme was identified as b-type dihydroorotate dehydrogenase (DHODb) and characterized as a dominant H₂O₂ producer in B. bifidum. In this study, we performed further purification of the enzyme from the NAD(P)H oxidase-active fraction and characterized the purified enzyme as a part of the H₂O₂ degradation system in B. bifidum. This purified enzyme was identified as thioredoxin reductase (TrxR); the NAD(P)H oxidase activity of this enzyme was not expressed in anaerobically grown B. bifidum, and mRNA expression was induced by O₂ exposure. Furthermore, the purified B. bifidum TrxR interacted with recombinant alkyl hydroperoxide reductase (rAhpC) and exhibited NAD(P)H peroxidase activity. These results suggest that TrxR responds to O₂ and protects B. bifidum from oxidative stress by degrading H₂O₂ via the TrxR-AhpC system.

Redox chemistry of Mycobacterium tuberculosis alkylhydroperoxide reductase E (AhpE): Structural and mechanistic insight into a mycoredoxin-1 independent reductive pathway of AhpE via mycothiol

Mycobacterium tuberculosis (Mtb) has the ability to persist within the human host for a long time in a dormant stage and re-merges when the immune system is compromised. The pathogenic bacterium employs an elaborate antioxidant defence machinery composed of the mycothiol- and thioredoxin system in addition to a superoxide dismutase, a catalase, and peroxiredoxins (Prxs). Among the family of Peroxiredoxins, Mtb expresses a 1-cysteine peroxiredoxin, known as alkylhydroperoxide reductase E (MtAhpE), and defined as a potential tuberculosis drug target. The reduced MtAhpE (MtAhpE-SH) scavenges peroxides to become converted to MtAhpE-SOH. To provide continuous availability of MtAhpE-SH, MtAhpE-SOH has to become reduced. Here, we used NMR spectroscopy to delineate the reduced (MtAhpE-SH), sulphenic (MtAhpE-SOH) and sulphinic (MtAhpE-SO2H) states of MtAhpE through cysteinyl-labelling, and provide for the first time evidence of a mycothiol-dependent mechanism of MtAhpE reduction. This is confirmed by crystallographic studies, wherein MtAhpE was crystallized in the presence of mycothiol and the structure was solved at 2.43Å resolution. Combined with NMR-studies, the crystallographic structures reveal conformational changes of important residues during the catalytic cycle of MtAhpE. In addition, alterations of the overall protein in solution due to redox modulation are observed by small angle X-ray scattering (SAXS) studies. Finally, by employing SAXS and dynamic light scattering, insight is provided into the most probable physiological oligomeric state of MtAhpE necessary for activity, being also discussed in the context of concerted substrate binding inside the dimeric MtAhpE.

Serum Helicobacter pylori KatA and AhpC antibodies as novel biomarkers for gastric cancer

AIM: To investigate catalase (KatA) and alkyl hydroperoxide reductase (AhpC) antibodies of Helicobacter pylori as biomarkers for gastric cancer (GC).

METHODS: This study included 232 cases and 264 controls. Recombinant KatA and AhpC proteins were constructed and the levels of antibodies were tested by indirect enzyme-linked immunosorbent assay (ELISA). Logistic regression was applied to analyze the relationships between KatA, AhpC and GC. The χ² trend test was used to evaluate the dose-response relationships between serum KatA and AhpC antibody levels and GC. Receiver operating characteristic (ROC) curve was used to evaluate the screening accuracy of KatA and AhpC as biomarkers. Combined analysis was used to observe screening accuracy of predictors for GC.

RESULTS: In all subjects, the association between KatA and AhpC and GC risk was significant (P < 0.001) with odds ratio (OR) = 12.84 (95%CI: 7.79-21.15) and OR = 2.4 (95%CI: 1.55-3.73), respectively. KatA and AhpC antibody levels were strongly related to GC risk with a dose-dependent effect (P for trend < 0.001). The area under the ROC (AUC) for KatA was 0.806, providing a sensitivity of 66.81% and specificity of 86.36%; and the AUC for AhpC was 0.615, with a sensitivity of 75.65% and specificity of 45.49%. The AUC was 0.906 for KatA and flagella protein A (FlaA) combined analysis.

CONCLUSION: Serum KatA and AhpC antibodies are associated with GC risk and KatA may serve as a biomarker for GC. KatA/FlaA combined analysis improved screening accuracy.

Mutation of alkyl hydroperoxide reductase gene ahpC of Xanthomonas oryzae pv. oryzae affects hydrogen peroxide accumulation during the rice-pathogen interaction

Hydrogen peroxide (H2O2) is usually generated by normal aerobic respiration of pathogens and by the host defense response during plant-pathogen interactions. In this study, histochemical localization of H2O2 accumulation in rice inoculated with the wild-type strain (PXO99(A)) and the gene deletion mutant (ΔahpC) of alkyl hydroperoxide reductase subunit C (AhpC) of Xanthomonas oryzae pv. oryzae (Xoo), the bacterial blight pathogen of rice, was analyzed. The ΔahpC mutant displayed a significant decrease in endogenous H2O2 accumulation which was induced by the compensatory increase in H2O2 scavenging activity. The change in the bacterial endogenous H2O2 level affected the total amount of H2O2 accumulation during the interaction with rice plants. These results suggested that Xoo contributes to H2O2 accumulation in rice in a compatible interaction, and pathogen-driving H2O2 is in association with cell collapse of rice.

Homologous overexpression of alkyl hydroperoxide reductase subunit C (ahpC) protects Bifidobacterium longum strain NCC2705 from oxidative stress

The ability to manage reactive oxygen species (ROS) effectively is crucial for the survival of gut bifidobacteria under conditions of oxidative stress. Alkyl hydroperoxide reductase catalytic subunit C (ahpC) of Bifidobacterium longum responds to various oxidative stresses. In this study, an ahpC-overexpressing transformant of B. longum strain NCC2705 was constructed to investigate the role and function of ahpC in oxidative stresses inflicted by treatments with hydrogen peroxide (H2O2), cumene hydroperoxide, and aerobic oxygen. Results indicated that in B. longum, AhpC is the primary scavenger of endogenous H2O2 generated by aerobic metabolism, but it is unable to detoxify high concentrations of exogenous H2O2. The ahpC-overexpressing B. longum strain showed increased resistance to organic hydroperoxide killing, increased viability under aerobic growth, but decreased resistance to exogenous H2O2 in comparison to the control strain. Analysis of genes from the oxidative stress-defense pathway encoding oxygen-independent coproporphyrinogen III oxidase (HemN), NADH oxidase (Nox) and thioredoxin reductase-like protein (TrxB) showed increased transcript levels in the ahpC-overexpressing vs. control strain. These findings suggest that elevated ahpC expression facilitates or activates the different electron donor-dependent ROS-elimination pathways in B. longum's response to oxidative stress.

Preparative SDS-PAGE Electroelution for Rapid Purification of Alkyl Hydroperoxide Reductase from Helicobacter pylori

BACKGROUND

Alkyl hydroperoxide reductase (AhpC) of Helicobacter pylori is considered as a diagnostic antigen. Therefore, this antigen can be used to detect H. pylori infection by stool immunoassays such as ELISA. The aim of this study was to simplify the AhpC protein purification procedures.

METHODS

For whole cell protein extraction, the bacterial cells were ruptured by octly-β-D glucopyranoside. The isolation and purification of AhpC protein were attempted by various techniques including ammonium sulfate precipitation, dialysis, preparative sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and electroelution.

RESULTS

A simple method was used for protein purification AhpC protein. One-dimensional preparative gel electrophoresis allows a single and short purification step; the high resolution capacity of this technique leads to a high level of purity of the protein. Moreover, it avoids contamination by other non-specific proteins which often appear during protein purification by column chromatography.

CONCLUSION

The present method is simple, rapid and makes it possible to preparate AhpC from H. pylori.