| Source (authors, year) | Publication type | Organism/strain | What was studied (exbB/exbD/tonB, operon) | Key findings (function/localization/phenotypes) | Key quantitative data/statistics | URL/DOI |
|---|---|---|---|---|---|---|
| Braun, Ratliff, Celia & Buchanan, 2023 | Peer-reviewed mechanistic review | Primarily *E. coli* / Gram-negative bacteria | ExbB-ExbD-TonB motor; adjacency of exbB and exbD; conserved TonB energization of TBDTs | ExbB and ExbD are inner-membrane proteins that use proton motive force to energize TonB, which contacts TonB boxes in outer-membrane TonB-dependent transporters for uptake of siderophores, vitamin B12, and other scarce nutrients; ExbB forms a pentameric motor surrounding an ExbD dimer; exb mutants have leaky/partial phenotypes and can be partly complemented by TolQ/TolR (pqac-00000001, pqac-00000002, pqac-00000006, pqac-00000007) | ExbB:ExbD stoichiometry reported as 5:2; exbB mutants retain ~20% cobalamin transport vs WT, while tonB or exbB tolQ double mutants fall to <5% (pqac-00000002) | https://doi.org/10.1128/jb.00035-23 |
| Braun, 2024 | Peer-reviewed review | Gram-negative bacteria | TonB-dependent transporters and ExbB-ExbD energy-transducing complex | TonB is energized by ExbB-ExbD to open plugged outer-membrane TBDTs; ExbB-ExbD supports uptake of Fe3+-siderophores, other metal ions, vitamin B12, glycans, and some proteins/toxins; model supports ExbB pentamer enclosing ExbD dimer (pqac-00000005) | ExbB complex described as five ExbB subunits around an ExbD dimer (pqac-00000005) | https://doi.org/10.1111/mmi.15332 |
| Weimer, 2024 | Experimental primary study / thesis-style report | *Pseudomonas putida* KT2440 | In-frame deletion of exbB-exbD-tonB (PP_5306-PP_5308); role in mediator uptake/electrogenic metabolism | Directly relevant to Q88C77 context: exbB is PP_5306 in the PP_5306-PP_5308 cluster. ΔexbBD ΔtonB impairs aerobic growth under baseline iron, lowers anaerobic ferricyanide reduction, reduces current generation, prolongs glucose conversion, and shifts product spectrum from 2-ketogluconate to gluconate, supporting a role in TonB-dependent uptake/handling of iron-linked or metal-mediator substrates (pqac-00000013, pqac-00000014, pqac-00000015) | Deletion size difference 2123 bp; mutant aerobic growth rate ~7-fold lower than WT at 5.5 µM FeCl3; 20 µM FeCl3 restores growth to ~80% of WT; anaerobic ferricyanide reduction 0.026 ± 0.001 mM/h vs WT 0.056 ± 0.009 mM/h; ferricyanide max current 1.0 ± 0.14 mA vs WT 2.42 ± 0.43 mA; 2-ketogluconate yield 0.17 ± 0.01 vs WT 0.93 ± 0.03 mol/mol glucose; glucose conversion prolonged to ~240 h vs ~186 h WT (pqac-00000013, pqac-00000014, pqac-00000015) | No DOI/URL available in retrieved context |
| Ainsaar et al., 2019 | Peer-reviewed primary study | *Pseudomonas putida* KT2440 | TonBm-PocAB system; genomic context of TonB homologs in KT2440 | Provides key locus context: *P. putida* has two TonB homologues, PP_4994 and PP_5308; PP_5308 (tonB) is in an operon with exbB and exbD, supporting assignment of Q88C77/PP_5306 as the cognate ExbB in the canonical exbBD-tonB operon. Study mainly analyzed the orthologous TonBm-PocAB system, showing TonB-like envelope motors can affect membrane integrity and flagellar positioning in *P. putida* (from retrieved abstract/snippet in paper search results) | Qualitative snippet only in retrieved context; no direct numeric exbB data available in cited evidence set | https://doi.org/10.1128/jb.00303-19 |
| Godoy, Ramos-González & Ramos, 2001 | Peer-reviewed primary study | *Pseudomonas putida* DOT-T1E (closely related to KT2440) | exbBD-tonB cluster organization and mutant phenotypes from exbD insertion | exbB, exbD, and tonB are closely linked and likely cotranscribed; the TonB-ExbB-ExbD complex is an inner-membrane energy transduction system required for iron uptake and additionally influences solvent/drug tolerance, likely via effects on efflux. Mutating exbD caused sensitivity to 4HBA, toluene, and multiple antibiotics and impaired growth in iron-limited medium; because DOT-T1E proteins are highly similar to KT2440 homologs, this is strong comparative evidence for PP_5306 function (pqac-00000000, pqac-00000003, pqac-00000008, pqac-00000009, pqac-00000016) | exbB-exbD separated by 3 bp; exbD and tonB overlap; mutant failed to grow in low iron with 8 mM EDDHA; [14C]4HBA accumulation ~200 nmol/U cell turbidity/min in mutant vs ~15 in control; high-affinity transport can generate up to 1,000-fold concentration gradients (pqac-00000000, pqac-00000008, pqac-00000016) | https://doi.org/10.1128/jb.183.18.5285-5292.2001 |
| Cornelis, 2010 | Peer-reviewed review | Pseudomonads including *P. putida* KT2440 | Iron uptake and metabolism; TonB-ExbB-ExbD support of siderophore/heme uptake | In pseudomonads, TonB together with ExbB and ExbD transmits pmf-derived energy from the inner membrane to outer-membrane receptors for ferric-siderophore and heme uptake. This review supports the inferred primary function of PP_5306/Q88C77 as an inner-membrane energy-coupling subunit for TonB-dependent iron acquisition rather than as a substrate-specific transporter itself (pqac-00000004) | Review notes gated OM receptors are 22-stranded β-barrels (pqac-00000004) | https://doi.org/10.1007/s00253-010-2550-2 |
| Villalobos-Escobedo et al., 2023 | Peer-reviewed primary study (RB-TnSeq) | *P. putida* KT2440 and other plant-associated bacteria | Genome-wide fitness under *Trichoderma atroviride* exometabolites; iron uptake functions | In the mixed-species analysis, TonB/ExbB/ExbD-dependent siderophore transport was especially important in the nitrogen-fixing bacteria tested, while *P. putida* showed dependence on membrane lipid modification pathways overall; additional inspection indicated iron-uptake genes were required for *P. putida* fitness in fungal exudates, consistent with ecological importance of TonB-linked iron acquisition even if exbB was not the dominant hit in the summary text (pqac-00000010, pqac-00000011, pqac-00000012) | Significant fitness thresholds were log2 fitness < -1 with t-score < -4 for negative hits; 41 *P. putida* genes had negative fitness under the stated filter in spent medium experiments (pqac-00000010, pqac-00000012) | https://doi.org/10.1371/journal.pgen.1010909 |


*Table: This table summarizes the main mechanistic and organism-specific sources relevant to annotation of *Pseudomonas putida* KT2440 exbB (PP_5306; UniProt Q88C77). It highlights evidence for operon context, inner-membrane localization, pmf-coupled TonB energization, and experimentally observed phenotypes when the exbBD-tonB system is disrupted.*