| Annotation aspect | Summary for **Pseudomonas putida** KT2440 **fpvA** / **PP_4217** / UniProt **Q88F81** | Evidence / strength |
|---|---|---|
| Identity mapping | KT2440 literature explicitly identifies **fpvA = PP4217** and annotates it as the **iron-pyoverdine complex receptor**; this matches the UniProt entry for Q88F81 and distinguishes it from homologous **fpvA** genes studied in other *Pseudomonas* species (pqac-00000018) | **Direct KT2440-specific annotation** from primary literature; high confidence for locus-to-gene mapping (pqac-00000018) |
| Protein type / family / domains | FpvA belongs to the **TonB-dependent outer-membrane receptor** family. Canonical architecture includes a **22-stranded β-barrel**, an internal **plug domain**, and an N-terminal **TonB box** required for interaction with TonB; FpvA-class receptors can also include an **additional N-terminal signaling domain** implicated in cell-surface signaling/transduction (pqac-00000003, pqac-00000004, pqac-00000013) | **Indirect for KT2440, strong by homology/family conservation**; domain architecture is well established for FpvA/TBDTs, though mostly from non-KT2440 systems (pqac-00000003, pqac-00000004, pqac-00000013) |
| Primary substrate | Primary inferred substrate is **ferric pyoverdine** (the **iron-pyoverdine / ferri-pyoverdine complex**), consistent with the explicit KT2440 annotation “iron-pyoverdine complex receptor” and with FpvA function across fluorescent pseudomonads (pqac-00000018, pqac-00000002, pqac-00000006) | **Direct KT2440 annotation + strong comparative support**; no substrate-switch evidence found for PP_4217 (pqac-00000018, pqac-00000002) |
| Cellular localization | FpvA is expected to reside in the **outer membrane** as a siderophore receptor. Its **TonB box** engages **TonB** in the periplasmic space, and transport is energized by the **TonB–ExbB–ExbD** complex using inner-membrane proton motive force; substrate first binds extracellular loops/plug, then is translocated to the periplasm (pqac-00000003, pqac-00000004, pqac-00000005, pqac-00000006) | **Indirect for KT2440 but mechanistically very strong** from TonB-dependent receptor literature and FpvA studies (pqac-00000004, pqac-00000005, pqac-00000006) |
| Immediate biochemical role | FpvA mediates the **outer-membrane uptake step** of iron acquisition by recognizing ferri-pyoverdine outside the cell and enabling its transfer into the periplasm; it is therefore a **transporter/receptor**, not an enzyme catalyzing a chemical transformation (pqac-00000002, pqac-00000005, pqac-00000006) | **Strong family-level functional evidence**; exact transport cycle in KT2440 inferred from homologous FpvA/TBDT systems (pqac-00000002, pqac-00000006) |
| Pathway context | KT2440 produces **pyoverdine** and carries pyoverdine genes in **three clusters**: **PP4243–4246, PP4319–4327, and PP4219–4223**. The main pyoverdine transcriptional activator **prfI (PP4244)** is an ECF σ factor homologous to **PvdS**; KT2440 also encodes many TonB-dependent siderophore receptors, placing FpvA within a larger iron-scavenging network (pqac-00000022, pqac-00000021, pqac-00000023) | **Direct KT2440 genomic context** for the pyoverdine system, though PP_4217 itself is not deeply characterized genetically in these studies (pqac-00000022, pqac-00000021) |
| Regulation / iron control | In pseudomonads, pyoverdine production and uptake genes are primarily controlled by the global iron regulator **Fur**, which modulates ECF σ-factor pathways under iron limitation; KT2440 pyoverdine circuitry includes **PfrI/PrfI (PvdS homolog)** and **PP_4208 (FpvI)** as regulators in the broader system (pqac-00000022, pqac-00000001, pqac-00000008) | **Direct/near-direct KT2440 systems-level evidence** for regulatory framework; specific promoter-level data for PP_4217 remain limited (pqac-00000022, pqac-00000001) |
| Cell-surface signaling concept | FpvA-like receptors can function not only as transporters but also as **cell-surface signaling (CSS) transducers**, where ligand detection at the outer membrane influences transcription of uptake genes through anti-σ / ECF σ pathways. Recent work in *P. aeruginosa* revises CSS models by showing pre-existing receptor–anti-σ interactions and receptor proteolysis effects (pqac-00000002, pqac-00000013) | **Conceptually relevant but mostly non-KT2440 evidence**; useful for functional inference, not direct proof for PP_4217 behavior in KT2440 (pqac-00000002, pqac-00000013) |
| Downregulation under aromatic stress | A KT2440 transcriptomics study reports that **fpvA (PP4217)**, annotated as the **iron-pyoverdine complex receptor**, was **“tuned down in the presence of 3MB”** (3-methylbenzoate), alongside other TonB-dependent receptors, during conditions associated with oxidative stress and reduced iron-acquisition functions (pqac-00000018) | **Direct KT2440 expression evidence**, but condition-specific and not a dedicated iron-uptake study (pqac-00000018) |
| Broader KT2440-specific support | KT2440 devotes major genomic capacity to iron scavenging: reports cite **29 predicted TonB-dependent outer-membrane siderophore receptors** (and another passage notes **18 outer-membrane ferric/ferric-related siderophore receptors**), consistent with ecological adaptation to iron limitation and receptor diversification in rhizosphere/dilute environments (pqac-00000021, pqac-00000023) | **Direct KT2440 genome-based evidence** supporting biological plausibility of fpvA as an iron receptor (pqac-00000021, pqac-00000023) |
| Recent 2023–2024 relevance | Recent work emphasizes that TonB-dependent receptors are dynamically regulated, structurally complex uptake gates and attractive translational targets. Quantitative examples include **sigmoidal vs logarithmic TBDT transcriptional responses**, **maximal pfeA induction at ~3 µM enterobactin**, and receptor diversity across **94 pyoverdine receptor groups** predicted from **1,928 Pseudomonas genomes** with **151 new pyoverdine structures** and **91 new receptor groups** (pqac-00000009, pqac-00000015) | **Recent authoritative context**, not KT2440-specific for fpvA function, but highly relevant for current understanding of receptor specificity/evolution/application (pqac-00000009, pqac-00000015) |
| Overall functional annotation | **Best-supported annotation:** FpvA (Q88F81/PP_4217) is a **TonB-dependent outer-membrane ferri-pyoverdine receptor** in **P. putida KT2440**, functioning in **iron acquisition** under iron limitation and likely integrated with **Fur/ECF σ-factor regulation** and possibly **cell-surface signaling**. The strongest KT2440-specific evidence is **gene identity/annotation** and **condition-dependent transcriptional downregulation**, whereas detailed transport mechanism is inferred from homologous FpvA/TBDT studies (pqac-00000018, pqac-00000022, pqac-00000003, pqac-00000004, pqac-00000006) | **High confidence for core function/localization; moderate confidence for detailed regulatory/mechanistic specifics in KT2440 due to limited direct experiments** (pqac-00000018, pqac-00000022, pqac-00000003, pqac-00000006) |


*Table: This table summarizes the best-supported functional annotation for Pseudomonas putida KT2440 fpvA (Q88F81/PP_4217), integrating direct KT2440 evidence with mechanistic inference from authoritative TonB-dependent receptor and FpvA literature. It is useful for quickly separating high-confidence organism-specific facts from broader homolog-based functional interpretation.*