Bcp (bacterioferritin comigratory protein) is a monomeric peroxiredoxin of the BCP/PrxQ subfamily (EC 1.11.1.24) that catalyzes the thioredoxin-dependent reduction of hydrogen peroxide and organic hydroperoxides to water and the corresponding alcohols. It functions as an atypical 2-Cys peroxiredoxin: the peroxidatic cysteine Cys45 is oxidized to sulfenic acid by peroxide, then forms an intramolecular disulfide with the resolving cysteine Cys50, which is subsequently reduced by thioredoxin. Unlike the major E. coli peroxiredoxin AhpC, BCP is unusually versatile -- it can use multiple electron donors (Trx1, Trx2, Grx1, Grx3), has the highest redox potential (-146 mV) of any characterized peroxiredoxin, and shows broad peroxide substrate specificity. These properties suggest BCP may serve as a defense enzyme of last resort, remaining active under highly oxidizing conditions when other antioxidant systems are compromised. The bcp null mutant shows hypersensitivity to H2O2, tert-butyl hydroperoxide, and linoleic acid hydroperoxide, confirming its role in oxidative stress defense.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0008379 thioredoxin peroxidase activity | IBA GO_REF:0000033 | ACCEPT | Summary: BCP has well-characterized thioredoxin-dependent peroxidase activity. The IBA annotation from phylogenetic inference is strongly supported by direct experimental evidence in the same organism (see IDA annotation below). BCP uses thioredoxin as a primary electron donor to reduce hydroperoxides. Reason: Thioredoxin peroxidase activity is the core molecular function of BCP, demonstrated by Jeong et al. (2000) and characterized in detail by Reeves et al. (2011). The phylogenetic inference is correct and consistent with direct experimental data. Supporting Evidence: PMID:10644761 BCP showed a thioredoxin-dependent thiol peroxidase activity PMID:21910476 thioredoxin (Trx1)-dependent peroxidase assays conducted by stopped-flow spectroscopy file:ECOLI/bcp/bcp-deep-research-falcon.md described as an unusually versatile bacterial peroxiredoxin |
| GO:0005737 cytoplasm | IBA GO_REF:0000033 | ACCEPT | Summary: Cytoplasmic localization is correct for BCP. The protein lacks signal peptides and transmembrane domains and is a soluble monomeric enzyme. Two independent proteomics studies confirmed cytosolic localization. The broader cytoplasm annotation subsumes the more specific cytosol IDA annotations. Reason: BCP is a soluble cytoplasmic enzyme. This is supported by two independent large-scale proteomics studies that identified BCP in the cytosolic fraction of E. coli K-12. Supporting Evidence: PMID:15911532 a proteomic analysis of Escherichia coli in which 3,199 protein forms were detected, and of those 2,160 were annotated and assigned to the cytosol, periplasm, inner membrane, and outer membrane PMID:18304323 we identified 1103 proteins from the cytosolic fraction of the Escherichia coli strain MC4100 file:ECOLI/bcp/bcp-deep-research-falcon.md BCP is best supported as a **cytosolic peroxide-detoxifying enzyme** integrated with NADPH-driven thioredoxin/glutaredoxin systems |
| GO:0034599 cellular response to oxidative stress | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: BCP is involved in the cellular response to oxidative stress. The bcp null mutant shows hypersensitivity to multiple oxidants, and bcp expression is induced 3-fold upon shift from anaerobic to aerobic growth. However, GO:0034599 (cellular response to oxidative stress) implies a signaling or regulatory response component beyond simple detoxification. While UniProt states BCP acts "as sensor of hydrogen peroxide-mediated signaling events," the evidence for a signaling role in E. coli BCP is limited. The more straightforward annotation GO:0006979 (response to oxidative stress, IMP) is already present and better supported. Reason: The annotation is not wrong but the more specific claim of "cellular response" (implying regulation/signaling) is less well-supported than the general oxidative stress response role. The IMP annotation to GO:0006979 below provides stronger direct evidence for the core oxidative stress defense function. Supporting Evidence: PMID:10644761 BCP was induced 3-fold by the oxidative stress given by changing the growth conditions from the anaerobic to aerobic culture |
| GO:0045454 cell redox homeostasis | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: BCP participates in maintaining cellular redox balance through its peroxidase activity, cycling between reduced and oxidized states via the thioredoxin system. The unusually high redox potential (-146 mV) and ability to use multiple electron donors (Trx1, Trx2, Grx1, Grx3) suggest BCP integrates with the broader cellular redox network. Reason: While BCP does cycle through the thioredoxin/glutaredoxin redox systems, its primary evolved function is peroxide detoxification rather than general redox homeostasis. This annotation is technically correct but secondary to the core peroxidase function. Supporting Evidence: PMID:21910476 BCP can utilize a variety of reducing substrates, including Trx1, Trx2, Grx1, and Grx3 PMID:21910476 BCP exhibited a high redox potential of -145.9 ± 3.2 mV, the highest to date observed for a Prx file:ECOLI/bcp/bcp-deep-research-falcon.md Bcp can also use Trx2 and glutaredoxins Grx1 and Grx3 as alternative reducing partners, indicating relaxed reductant specificity. |
| GO:0016209 antioxidant activity | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: BCP is indeed an antioxidant enzyme that detoxifies reactive oxygen species. This IEA annotation from InterPro (IPR000866, AhpC/TSA domain) is correct but very general. The more specific annotations for thioredoxin peroxidase activity (GO:0008379) and thioredoxin-dependent peroxiredoxin activity (GO:0140824) provide better functional resolution. Reason: Correct but too general. The specific peroxidase activity terms (GO:0008379, GO:0140824) are more informative for describing BCP function. Retained as a broad parent annotation from InterPro2GO. |
| GO:0016491 oxidoreductase activity | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: BCP is an oxidoreductase (EC 1.11.1.24). This IEA annotation from InterPro is correct but extremely general. It is fully subsumed by the more specific thioredoxin peroxidase activity annotations. The falcon deep research confirms the precise activity (atypical 2-Cys peroxiredoxin reducing peroxides), making this grandparent term redundant for curation purposes. Reason: Uninformatively broad grandparent term, fully subsumed by the specific molecular function annotations (GO:0008379, GO:0140824) that capture the experimentally characterized thioredoxin-dependent peroxidase reaction. This IEA term adds no curation value beyond the specific peroxidase terms. Supporting Evidence: file:ECOLI/bcp/bcp-deep-research-falcon.md classification as an **atypical 2-Cys peroxiredoxin** with a **Cp–Cr** motif |
| GO:0098869 cellular oxidant detoxification | IEA GO_REF:0000120 | ACCEPT | Summary: BCP detoxifies cellular oxidants (H2O2 and organic hydroperoxides) by reducing them to water and alcohols. This is a core biological process annotation that accurately describes BCP function. The combined IEA annotation derives from the molecular function annotations (GO:0008379, GO:0016209, GO:0140824). Reason: Cellular oxidant detoxification is a core biological function of BCP. The bcp null mutant shows hypersensitivity to H2O2, t-butyl hydroperoxide, and linoleic acid hydroperoxide, directly demonstrating BCP detoxifies these oxidants. Supporting Evidence: PMID:10644761 Bcp null mutant grew more slowly than its wild type in aerobic culture and showed the hypersensitivity toward various oxidants such as H(2)O(2), t-butyl hydroperoxide, and linoleic acid hydroperoxide |
| GO:0140824 thioredoxin-dependent peroxiredoxin activity | IEA GO_REF:0000120 | ACCEPT | Summary: GO:0140824 corresponds to EC 1.11.1.24 and represents the specific catalytic reaction: hydroperoxide + [thioredoxin]-dithiol = alcohol + [thioredoxin]-disulfide + H2O. This is the most precise molecular function term for BCP and directly matches the experimentally characterized activity. Reason: This is the most specific and accurate MF term for BCP. EC 1.11.1.24 is assigned to BCP with experimental evidence (PMID:10644761, PMID:21910476). BCP uses the thioredoxin system as its primary electron donor, making this the correct EC-linked GO term. Supporting Evidence: PMID:10644761 BCP showed a thioredoxin-dependent thiol peroxidase activity PMID:21910476 Kinetic and thermodynamic features reveal that Escherichia coli BCP is an unusually versatile peroxiredoxin file:ECOLI/bcp/bcp-deep-research-bioreason-sft.md domain logic directly yields the molecular functions formalized as GO:0008379 thioredoxin peroxidase activity file:ECOLI/bcp/bcp-deep-research-falcon.md classification as an **atypical 2-Cys peroxiredoxin** with a **Cp–Cr** motif |
| GO:0005829 cytosol | IDA PMID:15911532 Localization, annotation, and comparison of the Escherichia ... | ACCEPT | Summary: Lopez-Campistrous et al. (2005) identified BCP in the cytosolic fraction of E. coli K-12 by 2D-gel electrophoresis and tandem mass spectrometry after biochemical fractionation. This is direct experimental evidence for cytosolic localization. Reason: Direct identification of BCP in the cytosolic fraction by biochemical fractionation followed by 2D-gel/MS/MS. BCP lacks signal peptides and transmembrane domains, consistent with soluble cytosolic localization. Supporting Evidence: PMID:15911532 a proteomic analysis of Escherichia coli in which 3,199 protein forms were detected, and of those 2,160 were annotated and assigned to the cytosol, periplasm, inner membrane, and outer membrane |
| GO:0005829 cytosol | IDA PMID:18304323 Protein abundance profiling of the Escherichia coli cytosol. | ACCEPT | Summary: Ishihama et al. (2008) independently identified BCP in the cytosolic fraction of E. coli MC4100 by LC-MS/MS. This provides independent confirmation of cytosolic localization from a second proteomics study. Reason: Independent confirmation of cytosolic localization using LC-MS/MS on the cytosolic fraction. Consistent with the other IDA annotation from PMID:15911532 and with the absence of signal peptide or transmembrane domains. Supporting Evidence: PMID:18304323 we identified 1103 proteins from the cytosolic fraction of the Escherichia coli strain MC4100 |
| GO:0006979 response to oxidative stress | IMP PMID:10644761 Thioredoxin-dependent hydroperoxide peroxidase activity of b... | ACCEPT | Summary: The bcp null mutant showed clear hypersensitivity to oxidative stress: slower growth in aerobic culture and increased sensitivity to H2O2, t-butyl hydroperoxide, and linoleic acid hydroperoxide. BCP expression was induced 3-fold upon shift from anaerobic to aerobic conditions. Complementation with bcp gene restored resistance. This is strong IMP (mutant phenotype) evidence. Reason: Strong mutant phenotype evidence. The bcp null mutant has clear oxidative stress hypersensitivity that is complemented by bcp expression, directly demonstrating BCP participates in the response to oxidative stress. Supporting Evidence: PMID:10644761 Bcp null mutant grew more slowly than its wild type in aerobic culture and showed the hypersensitivity toward various oxidants such as H(2)O(2), t-butyl hydroperoxide, and linoleic acid hydroperoxide PMID:10644761 The peroxide hypersensitivity of the null mutant could be complemented by the expression of bcp gene |
| GO:0008379 thioredoxin peroxidase activity | IDA PMID:10644761 Thioredoxin-dependent hydroperoxide peroxidase activity of b... | ACCEPT | Summary: Jeong et al. (2000) directly demonstrated thioredoxin-dependent peroxidase activity of purified recombinant BCP. BCP reduced H2O2, t-butyl hydroperoxide, and linoleic acid hydroperoxide using thioredoxin as electron donor. The C45S mutation abolished activity, confirming Cys-45 as the catalytic peroxidatic cysteine. Reason: Direct biochemical demonstration of thioredoxin-dependent peroxidase activity using purified protein and multiple peroxide substrates. This is the primary IDA evidence establishing BCP as a thiol-specific peroxidase and the core molecular function of the protein. Supporting Evidence: PMID:10644761 BCP showed a thioredoxin-dependent thiol peroxidase activity PMID:10644761 Replacement of Cys-45 with serine resulted in the complete loss of thiol peroxidase activity |
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Download this section (compressed HTML)Q: What are the relative contributions of BCP, AhpC, and Tpx to peroxide detoxification in E. coli under different stress conditions?
Suggested experts: Poole LB
Q: Does BCP have a signaling role in E. coli (as suggested by UniProt description of H2O2 sensor function), or is its role purely detoxification?
Suggested experts: Poole LB, Kim IH
Experiment: Compare peroxide sensitivity and survival of wild-type, bcp-null, ahpC-null, and bcp/ahpC double mutant E. coli under increasing concentrations of H2O2 and organic hydroperoxides. Measure the oxidation state of BCP and AhpC under progressive oxidative stress to determine if BCP remains active when AhpC is overoxidized.
Hypothesis: BCP serves as a "last resort" peroxidase under severe oxidative stress when AhpC is inactivated by overoxidation.
Type: genetic epistasis / redox proteomics
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