| Aspect | Key points | Best supporting sources (with year) | URLs/DOIs |
|---|---|---|---|
| Identity | UniProt Q88DT9 corresponds to **Fur, ferric uptake regulator**, in *Pseudomonas putida* KT2440 (gene **fur**, locus **PP_4730** per supplied target context). Evidence directly supporting KT2440 Fur function is organism-specific for iron-responsive regulation, though explicit PP_4730 naming was limited in retrieved papers. Fur-family assignment is strongly supported by conserved two-domain Fur architecture and iron-homeostasis role. (pqac-00000004, pqac-00000009) | Chen et al., 2010; Kang et al., 2024 | https://doi.org/10.1128/AEM.00215-10; https://doi.org/10.3390/biom14080981 |
| Molecular function | Fur is a **metal-dependent transcriptional regulator** that usually represses iron-acquisition genes when metal bound; it can also positively affect some genes indirectly. In KT2440, Fur positively affects **bfrα/bfrβ** expression, even though upstream canonical Fur boxes were not detected, implying indirect or noncanonical control. (pqac-00000004, pqac-00000005, pqac-00000008, pqac-00000015) | Chen et al., 2010; Steingard & Helmann, 2023 | https://doi.org/10.1128/AEM.00215-10; https://doi.org/10.1128/JB.00022-23 |
| Metal sensing | Fur proteins have conserved metal-binding sites **S1/S2/S3**; **S2** is the key regulatory iron-sensing site, while S1 often contributes structural stability and S3 can modulate conformation/oligomerization. Metal loading converts Fur from a less DNA-binding-competent open state to a DNA-binding-competent closed state. Reported affinities in structural studies show Zn²⁺ can bind more tightly than Fe²⁺/Mn²⁺ in some homologs. (pqac-00000009, pqac-00000013, pqac-00000014, pqac-00000015) | Kang et al., 2024; Steingard & Helmann, 2023 | https://doi.org/10.3390/biom14080981; https://doi.org/10.1128/JB.00022-23 |
| DNA binding / Fur box | Fur has an N-terminal DNA-binding domain and C-terminal dimerization domain; it typically binds DNA as a dimer or dimer-of-dimers. Canonical Fur boxes are described as a **19-bp inverted repeat** or overlapping **7-1-7 motifs** with consensus like **TGATAATnATTATCA** / **GATAATGATAATCATTATC**. For KT2440 **bfrα/bfrβ**, no canonical Fur box was detected, suggesting noncanonical or indirect regulation. (pqac-00000008, pqac-00000011, pqac-00000013, pqac-00000016) | Chen et al., 2010; Kang et al., 2024; Steingard & Helmann, 2023 | https://doi.org/10.1128/AEM.00215-10; https://doi.org/10.3390/biom14080981; https://doi.org/10.1128/JB.00022-23 |
| Regulon examples | Best-supported KT2440 targets from retrieved evidence are **bfrα** and **bfrβ** (bacterioferritins), positively influenced by Fur. More broadly in pseudomonads, Fur controls iron-acquisition circuits including siderophore pathways via regulators such as **pvdS/pchR** in *P. aeruginosa*; this supports cautious inference that KT2440 Fur sits upstream of iron uptake and storage homeostasis, but organism-specific direct regulon mapping remains limited here. (pqac-00000004, pqac-00000005, pqac-00000003) | Chen et al., 2010; Ochsner et al., 1995 | https://doi.org/10.1128/AEM.00215-10; https://doi.org/10.1128/JB.177.24.7194-7201.1995 |
| Localization | Fur is a **cytosolic DNA-binding regulator** acting on chromosomal promoters/operator regions. Its function depends on intracellular metal availability rather than secretion or membrane localization. (pqac-00000009, pqac-00000011, pqac-00000015) | Kang et al., 2024; Steingard & Helmann, 2023 | https://doi.org/10.3390/biom14080981; https://doi.org/10.1128/JB.00022-23 |
| Phenotypes | In KT2440, loss of Fur is associated with **greater H₂O₂ sensitivity** than bacterioferritin mutants, consistent with a broader iron/ROS homeostasis role. Fur-dependent control of bacterioferritins supports tolerance to iron starvation and oxidative stress indirectly through proper iron storage/homeostasis. (pqac-00000005, pqac-00000007) | Chen et al., 2010 | https://doi.org/10.1128/AEM.00215-10 |
| Quantitative data | In KT2440, under high-iron conditions, **bfrα** and **bfrβ** expression were about **3-fold** and **6-fold** higher in Fur⁺ than Fur⁻ cells; under low iron, differences were ~**0.5-fold** and **1.2-fold**. Single **bfr** mutants had ~**16–18%** lower cellular iron, while the double mutant had ~**38%** lower iron; Fur mutant H₂O₂ inhibition zone was ~**5.6 cm** vs ~**3.5 ± 0.2 cm** for bacterioferritin mutants. (pqac-00000004, pqac-00000005, pqac-00000006) | Chen et al., 2010 | https://doi.org/10.1128/AEM.00215-10 |
| Recent developments 2023-2024 | Recent reviews refined Fur understanding by emphasizing **metal-dependent conformational switching**, multiple metal sites, **dimer/tetramer** behavior, and nuanced operator architectures; Fur-family proteins are now viewed as broader **signaling hubs** integrating iron with other regulators and ligands. These advances strengthen functional inference for KT2440 Fur even where direct 2023-2024 KT2440 primary studies are sparse. (pqac-00000009, pqac-00000010, pqac-00000015, pqac-00000016) | Steingard & Helmann, 2023; Kang et al., 2024 | https://doi.org/10.1128/JB.00022-23; https://doi.org/10.3390/biom14080981 |


*Table: This table summarizes the best-supported functional annotation for *Pseudomonas putida* KT2440 Fur (UniProt Q88DT9), separating direct KT2440 evidence from broader Fur-family mechanistic inference. It is useful for quickly identifying molecular function, regulatory logic, phenotypes, and the strongest recent sources.*