NaBBL_candidate_FOX2_2 is a FOX2-branch BBL-family oxidoreductase candidate in Nicotiana attenuata. BBL-family late-pathway involvement is now supported, but FOX2_2 remains one of several unresolved paralogs rather than a uniquely identified nicotine oxidase.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
|
GO:0005773
vacuole
|
IEA
GO_REF:0000044 |
KEEP AS NON CORE |
Summary: Vacuolar localization is plausible contextual information.
Reason: The location is reasonable, but it is not the main discriminating evidence for this paralog.
|
|
GO:0016491
oxidoreductase activity
|
IEA
GO_REF:0000002 |
MARK AS OVER ANNOTATED |
Summary: This parent redox term is too generic for the current pathway model.
Reason: BBL-family proteins are now tied to a specific late oxidation role in nicotine synthesis.
Supporting Evidence:
file:NICAT/NaBBL_candidate_FOX2_2/NaBBL_candidate_FOX2_2-notes.md
The full preprint places a BBL-family enzyme directly in the nicotine synthase cascade as NicGS, with structural support and clear effects on stereoselective product formation.
|
|
GO:0050660
flavin adenine dinucleotide binding
|
IEA
GO_REF:0000002 |
ACCEPT |
Summary: FAD binding is appropriate for this flavoprotein.
Reason: This is an informative cofactor annotation for a BBL-family oxidoreductase.
|
|
GO:0071949
FAD binding
|
IEA
GO_REF:0000002 |
REMOVE |
Summary: This term duplicates GO:0050660.
Reason: Use GO:0050660 as the preferred cofactor-binding term and drop the redundant duplicate.
|
|
GO:0042179
nicotine biosynthetic process
|
IEA
GO_REF:0000041 |
KEEP AS NON CORE |
Summary: FOX2_2 is a plausible nicotine-pathway candidate but not a uniquely resolved one.
Reason: Family-level pathway support is strong, but specific paralog identity in NICAT remains open.
Supporting Evidence:
file:NICAT/NaBBL_candidate_FOX2_2/NaBBL_candidate_FOX2_2-notes.md
FOX2_2 therefore remains a plausible BBL-family paralog to evaluate, but the paper still leaves the exact NICAT paralog mapping unresolved.
|
Q: Is FOX2_2 biochemically capable of the NicGS-like oxidation step or is it a secondary duplicate?
Q: Does FOX2_2 show distinct expression or subfunctionalization compared with the FOX1-derived BBL candidates?
Experiment: Assay FOX2_2 in late-pathway reconstitution with A622, UGT, and BGL components.
Hypothesis: FOX2_2 retains partial BBL-like chemistry but is not the dominant attenuata late oxidase.
Type: pathway reconstitution assay
Experiment: Compare FOX2_2 expression and knockout phenotypes with FOX1_2 across nicotine-inducing conditions.
Hypothesis: FOX2_2 contributes less strongly than the leading BBL2-like anchor.
Type: comparative expression and genetics
The gene NaBBL_candidate_FOX2_2 in Nicotiana attenuata encodes a flavin-dependent oxidoreductase, as indicated by its UniProt accession number A0A314LBC4. This protein is characterized by several conserved domains, including the berberine bridge enzyme (BBE) domain (IPR012951) and the FAD-binding domains (IPR016166, IPR036318, IPR016167, IPR016169), suggesting its role in redox reactions involving flavin adenine dinucleotide (FAD) as a cofactor.
Protein Family and Domains
The presence of the BBE domain implies that NaBBL_candidate_FOX2_2 belongs to a family of enzymes known for catalyzing oxidation reactions, often involving alkaloid biosynthesis. The FAD-binding domains are indicative of the protein's ability to bind FAD, a common feature among oxidoreductases that participate in electron transfer processes.
Functional Inference from Homologous Proteins
While specific functional studies on NaBBL_candidate_FOX2_2 are lacking, insights can be drawn from homologous proteins in related species. For instance, in Nicotiana tabacum (common tobacco), a flavin-dependent oxidoreductase has been implicated in alkaloid metabolism, particularly in the biosynthesis of nicotine and related compounds. This enzyme is localized to the vacuole and is involved in the conversion of specific precursors into bioactive alkaloids. (db.cngb.org)
Additionally, a study on Nicotiana tabacum identified a soluble NAD(P)H:(quinone-acceptor) oxidoreductase that contains noncovalently bound flavin mononucleotide (FMN). This enzyme functions as a homotetramer and is involved in the reduction of quinones to hydroquinones, a process that prevents the formation of semiquinones and reactive oxygen species. (academic.oup.com)
Potential Biological Role in Nicotiana attenuata
Given the structural similarities and conserved domains, it is plausible that NaBBL_candidate_FOX2_2 serves a similar function in Nicotiana attenuata. The enzyme may participate in the biosynthesis of alkaloids, contributing to the plant's defense mechanisms against herbivores and pathogens. Its activity could involve the reduction of quinones, thereby mitigating oxidative stress within the plant cells.
Subcellular Localization
While direct evidence for the subcellular localization of NaBBL_candidate_FOX2_2 is not available, the vacuolar localization of its homologs in related species suggests a similar distribution. The vacuole is a key organelle for the storage and metabolism of secondary metabolites, including alkaloids, supporting the hypothesis of NaBBL_candidate_FOX2_2's involvement in these processes.
Conclusion
In summary, NaBBL_candidate_FOX2_2 in Nicotiana attenuata is likely a flavin-dependent oxidoreductase involved in alkaloid biosynthesis and oxidative stress mitigation. Its function can be inferred from conserved domains and homologous proteins in related species, although direct experimental evidence in Nicotiana attenuata is currently lacking.
id: A0A314LBC4
gene_symbol: NaBBL_candidate_FOX2_2
product_type: PROTEIN
status: DRAFT
aliases:
- FOX2_2
- NaBBL
taxon:
id: NCBITaxon:49451
label: Nicotiana attenuata
description: >-
NaBBL_candidate_FOX2_2 is a FOX2-branch BBL-family oxidoreductase candidate in
Nicotiana attenuata. BBL-family late-pathway involvement is now supported, but
FOX2_2 remains one of several unresolved paralogs rather than a uniquely
identified nicotine oxidase.
references:
- id: GO_REF:0000002
title: Gene Ontology annotation through association of InterPro records with GO terms
findings: []
- id: GO_REF:0000041
title: Gene Ontology annotation based on UniPathway vocabulary mapping
findings: []
- id: GO_REF:0000044
title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt
findings: []
- id: file:NICAT/NaBBL_candidate_FOX2_2/NaBBL_candidate_FOX2_2-uniprot.txt
title: UniProt entry A0A314LBC4 for Nicotiana attenuata FOX2_2
findings:
- statement: FOX2_2 is a BBL-family nicotine-associated oxidoreductase
supporting_text: Involved in the biosynthesis of pyridine alkaloid natural products, leading mainly to the production of anabasine, anatabine, nicotine and nornicotine ... Catalyzes a late oxidation step subsequent to the pyridine ring condensation reaction in the biosynthesis of alkaloids.
reference_section_type: DATABASE_ENTRY
- statement: UniProt places FOX2_2 in vacuole
supporting_text: 'CC -!- SUBCELLULAR LOCATION: Vacuole {ECO:0000256|ARBA:ARBA00004116}.'
reference_section_type: DATABASE_ENTRY
- id: file:NICAT/NaBBL_candidate_FOX2_2/NaBBL_candidate_FOX2_2-notes.md
title: NaBBL FOX2_2 candidate notes
findings:
- statement: BBL-family late-pathway chemistry is supported for FOX2_2-class paralogs
supporting_text: The full preprint places a BBL-family enzyme directly in the nicotine synthase cascade as NicGS, with structural support and clear effects on stereoselective product formation.
reference_section_type: LITERATURE_REVIEW
- statement: FOX2_2 remains unresolved at the specific NICAT paralog level
supporting_text: FOX2_2 therefore remains a plausible BBL-family paralog to evaluate, but the paper still leaves the exact NICAT paralog mapping unresolved.
reference_section_type: LITERATURE_REVIEW
existing_annotations:
- term:
id: GO:0005773
label: vacuole
evidence_type: IEA
original_reference_id: GO_REF:0000044
review:
summary: Vacuolar localization is plausible contextual information.
action: KEEP_AS_NON_CORE
reason: >-
The location is reasonable, but it is not the main discriminating evidence
for this paralog.
- term:
id: GO:0016491
label: oxidoreductase activity
evidence_type: IEA
original_reference_id: GO_REF:0000002
review:
summary: This parent redox term is too generic for the current pathway model.
action: MARK_AS_OVER_ANNOTATED
reason: >-
BBL-family proteins are now tied to a specific late oxidation role in
nicotine synthesis.
supported_by:
- reference_id: file:NICAT/NaBBL_candidate_FOX2_2/NaBBL_candidate_FOX2_2-notes.md
supporting_text: The full preprint places a BBL-family enzyme directly in the nicotine synthase cascade as NicGS, with structural support and clear effects on stereoselective product formation.
reference_section_type: LITERATURE_REVIEW
- term:
id: GO:0050660
label: flavin adenine dinucleotide binding
evidence_type: IEA
original_reference_id: GO_REF:0000002
review:
summary: FAD binding is appropriate for this flavoprotein.
action: ACCEPT
reason: >-
This is an informative cofactor annotation for a BBL-family oxidoreductase.
- term:
id: GO:0071949
label: FAD binding
evidence_type: IEA
original_reference_id: GO_REF:0000002
review:
summary: This term duplicates GO:0050660.
action: REMOVE
reason: >-
Use GO:0050660 as the preferred cofactor-binding term and drop the
redundant duplicate.
- term:
id: GO:0042179
label: nicotine biosynthetic process
evidence_type: IEA
original_reference_id: GO_REF:0000041
review:
summary: FOX2_2 is a plausible nicotine-pathway candidate but not a uniquely resolved one.
action: KEEP_AS_NON_CORE
reason: >-
Family-level pathway support is strong, but specific paralog identity in
NICAT remains open.
supported_by:
- reference_id: file:NICAT/NaBBL_candidate_FOX2_2/NaBBL_candidate_FOX2_2-notes.md
supporting_text: FOX2_2 therefore remains a plausible BBL-family paralog to evaluate, but the paper still leaves the exact NICAT paralog mapping unresolved.
reference_section_type: LITERATURE_REVIEW
core_functions:
- molecular_function:
id: GO:0016491
label: oxidoreductase activity
directly_involved_in:
- id: GO:0042179
label: nicotine biosynthetic process
description: >-
FOX2_2 is a BBL-family FAD-linked oxidoreductase candidate for the late
nicotine step, but its exact role relative to the other attenuata BBL
paralogs is unresolved.
supported_by:
- reference_id: file:NICAT/NaBBL_candidate_FOX2_2/NaBBL_candidate_FOX2_2-notes.md
supporting_text: The full preprint places a BBL-family enzyme directly in the nicotine synthase cascade as NicGS, with structural support and clear effects on stereoselective product formation.
reference_section_type: LITERATURE_REVIEW
proposed_new_terms: []
suggested_questions:
- question: Is FOX2_2 biochemically capable of the NicGS-like oxidation step or is it a secondary duplicate?
- question: Does FOX2_2 show distinct expression or subfunctionalization compared with the FOX1-derived BBL candidates?
suggested_experiments:
- description: Assay FOX2_2 in late-pathway reconstitution with A622, UGT, and BGL components.
experiment_type: pathway reconstitution assay
hypothesis: FOX2_2 retains partial BBL-like chemistry but is not the dominant attenuata late oxidase.
- description: Compare FOX2_2 expression and knockout phenotypes with FOX1_2 across nicotine-inducing conditions.
experiment_type: comparative expression and genetics
hypothesis: FOX2_2 contributes less strongly than the leading BBL2-like anchor.