FpvA (PP_4217) is a TonB-dependent outer membrane receptor of the ferripyoverdine receptor class. It is a large (812 aa) integral outer membrane protein built from a 22-stranded beta-barrel occluded by an N-terminal plug (cork) domain, together with a periplasmic TonB box and an N-terminal Secretin/TonB short (STN) signaling domain. FpvA functions in siderophore-mediated iron acquisition. It binds the ferric pyoverdine (iron-pyoverdine) complex at the cell surface and mediates its energy-dependent translocation across the outer membrane into the periplasm. Transport is energized by the inner-membrane TonB-ExbB-ExbD complex, which couples proton motive force to conformational changes in the plug/barrel via the receptor's TonB box. Members of this receptor class also act as cell-surface signaling transducers, where ligand recognition at the outer membrane can be transduced through an anti-sigma factor and ECF sigma factor cascade to regulate expression of pyoverdine biosynthesis and uptake genes. In P. putida KT2440, fpvA is part of an extensive iron-scavenging repertoire and is controlled by iron-responsive (Fur/ECF sigma) regulation.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0009279 cell outer membrane | IEA GO_REF:0000120 | ACCEPT | Summary: Correct subcellular location. FpvA is a TonB-dependent outer membrane receptor; the UniProt entry annotates Cell outer membrane and the protein has the canonical beta-barrel/plug architecture of an OM receptor. Reason: Consistent with the TonB-dependent receptor family, the multi-pass OM beta-barrel architecture, and UniProt subcellular location. This is the more specific and preferred CC term over GO:0019867. |
| GO:0015343 siderophore-iron transmembrane transporter activity | IEA GO_REF:0000002 | ACCEPT | Summary: Captures the core molecular function. FpvA mediates transport of the ferric-siderophore (ferripyoverdine) complex across the outer membrane. Reason: This term accurately describes the activity of a TonB-dependent ferri-siderophore receptor that imports the iron-loaded siderophore complex. Well supported by family/domain evidence (TonB-dependent siderophore receptor, IPR010105) and by the gene's identity as the ferripyoverdine receptor. |
| GO:0015344 siderophore uptake transmembrane transporter activity | IEA GO_REF:0000118 | ACCEPT | Summary: Also accurate; describes siderophore uptake transporter activity, consistent with the ferripyoverdine receptor function. Reason: TreeGrafter/PANTHER assignment consistent with the receptor's role in importing the ferripyoverdine complex. Closely related to GO:0015343; both are acceptable family-level MF terms for this receptor. |
| GO:0015891 siderophore transport | IEA GO_REF:0000002 | ACCEPT | Summary: Correct biological process. FpvA participates in transport of the pyoverdine siderophore (as the ferric complex) across the outer membrane. Reason: Directly supported by gene identity as ferripyoverdine receptor and TonB-dependent siderophore receptor domain evidence. |
| GO:0019867 outer membrane | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: Correct but less specific than GO:0009279 (cell outer membrane), which is also annotated. Reason: Not wrong, but GO:0009279 (cell outer membrane) is the preferred, more specific term for a Gram-negative bacterial outer membrane protein and is already present. Retained as a redundant parent rather than removed. |
| GO:0033214 siderophore-iron import into cell | IEA GO_REF:0000120 | ACCEPT | Summary: Accurate and specific biological process. FpvA imports the iron-siderophore (ferripyoverdine) complex into the cell (periplasm) as the first dedicated step of pyoverdine-mediated iron acquisition. Reason: Well supported; this is a more informative BP term than the parent GO:0015891 and matches the receptor's established role in ferric-pyoverdine import. |
| GO:0038023 signaling receptor activity | IEA GO_REF:0000002 | KEEP AS NON CORE | Summary: FpvA-class receptors carry an N-terminal signaling (STN) domain and can act as cell-surface signaling transducers, coupling ferripyoverdine recognition to ECF sigma/anti-sigma regulation of iron-uptake genes. The protein has the Secretin/TonB short N-terminal (STN) signaling domain (IPR011662). Reason: Cell-surface signaling is a plausible and domain-supported secondary function, but it is an IEA inference based on the STN domain and is not the receptor's core function (transport). There is no direct KT2440-specific experimental evidence that FpvA transduces a signal. Retained as a non-core, domain-inferred activity rather than removed. |
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