The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
The requested target is correctly identified as FliI, the flagellum-specific ATPase of Helicobacter pylori strain J99/ATCC 700824, encoded by jhp_1315 and represented by UniProt Q9ZJJ3. Its reported size—434 amino acids and approximately 47 kDa—its Walker/P-loop ATPase architecture, and its placement in the FliI/YscN family are all consistent with a flagellar type III secretion-system ATPase rather than an ATP synthase subunit or an unrelated same-symbol protein. No literature concerning a different “fliI” gene was used as organism-specific evidence. However, many detailed mechanistic conclusions still derive from Salmonella FliI and should be treated as strongly supported comparative inference rather than direct measurements on Q9ZJJ3. (ambilwade2016structuralcharacterizationof pages 35-40, ambilwade2016structuralcharacterizationofa pages 35-40, ambilwade2016structuralcharacterizationofa pages 40-45)
The most defensible primary annotation is:
A soluble, basal-body-associated Mg-ATPase that hydrolyzes ATP and couples flagellar export-substrate/chaperone recognition and export-gate activation to assembly of the H. pylori flagellum. It acts on the cytoplasmic side of the flagellar type III secretion system; ion motive force, rather than ATP hydrolysis alone, provides the principal energy for polypeptide translocation across the membrane.
| Annotation point | Conclusion | Evidence type | Strongest supporting study/date | Quantitative detail | Confidence / limitation |
|---|---|---|---|---|---|
| Exact identity | Target is FliI, UniProt Q9ZJJ3, locus jhp_1315, from Helicobacter pylori J99/ATCC 700824. | Database-supplied identity; literature-consistent | Supplied UniProt record; comparative J99/26695 genome analysis, 1999 | Q9ZJJ3; jhp_1315; strain J99 | High for database mapping. Most literature discusses H. pylori FliI without explicitly naming Q9ZJJ3. |
| Protein architecture | Soluble Walker-type, F1-like flagellar-export ATPase with an N-terminal partner-binding region, central nucleotide-hydrolysis domain, and helical C-terminal domain. | Direct H. pylori sequence characterization plus family inference | H. pylori export-apparatus characterization, 2016 (ambilwade2016structuralcharacterizationof pages 35-40, ambilwade2016structuralcharacterizationofa pages 35-40) | 434 aa; approximately 47 kDa; reported 26% identity to bovine F1-ATPase beta and 48% identity to Salmonella FliI (ambilwade2016structuralcharacterizationof pages 35-40, ambilwade2016structuralcharacterizationofa pages 40-45) | High for family assignment; moderate for domain boundaries transferred from homologs. |
| Catalytic reaction | Catalyzes magnesium-dependent ATP hydrolysis: ATP + H2O → ADP + phosphate + H+. ATP is the supported physiological nucleotide substrate. | Database annotation plus homolog inference | FliI biochemical and structural studies summarized in 2016 (ambilwade2016structuralcharacterizationof pages 40-45, ambilwade2016structuralcharacterizationof pages 35-40) | Conserved Walker A/P-loop and catalytic residues; no reliable Q9ZJJ3-specific Km, kcat, or nucleotide-selectivity panel found | High that it is an ATPase; exact kinetics and nucleotide selectivity remain unmeasured for Q9ZJJ3. |
| Flagellar-export requirement | FliI is necessary for efficient export of flagellar structural proteins and consequently for flagellum assembly. | Direct H. pylori genetic evidence | Jenks et al., 1997, FEMS Microbiology Letters, DOI (tsang2015basalbodystructures pages 10-10) | Disruption caused a flagellar-export defect; no trustworthy kinetic statistic recovered | High for H. pylori FliI generally; the retrieved text did not establish that the experimental allele was specifically J99 jhp_1315. |
| Cellular localization | Functions in the cytoplasm at the cytoplasmic face of the flagellar basal body and export gate, not as a transmembrane or extracellular subunit. | Homolog-derived localization model supported by H. pylori partner biology | FliH/FliI studies and current flagellar architecture literature, 2006–2024 (dhindwal2024helicobacterpyloriflgn pages 17-18, ambilwade2016structuralcharacterizationofa pages 35-40) | FliH links FliI to the C ring and export machinery | Moderate-to-high; direct in situ localization of Q9ZJJ3 itself was not found. |
| FliH interaction | H. pylori FliI binds the soluble export factor FliH through its N-terminal region; FliH regulates and recruits FliI to the export machinery. | Direct H. pylori interaction evidence; mechanistic details partly transferred from Salmonella | Lane, O'Toole and Moore, 2006, Journal of Biological Chemistry, DOI; supporting purification study, 2016 (dhindwal2024helicobacterpyloriflgn pages 17-18, ambilwade2016structuralcharacterizationof pages 115-118) | SEC detected an approximately 75-kDa FliH–FliI(E193Q) complex; exact stoichiometry was unresolved (ambilwade2016structuralcharacterizationof pages 115-118) | High for binding; moderate for regulatory mechanism; low for exact native stoichiometry. |
| FlgN interaction | The newly assigned H. pylori FlgN chaperone binds FliI or its N-terminal domain, supporting delivery of FlgN–FlgK complexes to the ATPase. | Direct H. pylori biochemical evidence | Dhindwal, Boniecki and Moore, January 2024, Protein Science 33:e4882, DOI (dhindwal2024helicobacterpyloriflgn pages 1-2) | FlgN–FlgK binding was nanomolar and 1:1; truncated FlgN bound FliI or FliI-N with sub-micromolar affinity (dhindwal2024helicobacterpyloriflgn pages 1-2) | High for in vitro interactions; moderate for the proposed in vivo delivery mechanism. |
| Oligomeric state | Active FliI is expected to assemble as an ATP-dependent homohexameric ring. | Primarily homolog inference | FliI oligomerization studies summarized in 2016 (ambilwade2016structuralcharacterizationof pages 40-45) | AMP-PNP increased complete ring yield about 20-fold in homolog studies (ambilwade2016structuralcharacterizationof pages 40-45) | High for the conserved family model but low-to-moderate for Q9ZJJ3 itself; purified H. pylori FliI(E193Q) appeared monomeric and did not form detectable hexamers under the tested conditions (ambilwade2016structuralcharacterizationof pages 115-118). |
| FliJ association | A canonical FliJ-like central stalk is expected to stabilize the FliI ring and connect it to FlhA and chaperone cycling, but the cognate H. pylori protein remains uncertain. | Homolog inference; uncertain H. pylori assignment | H. pylori structural and annotation analyses, 2016–2021 (dhindwal2021annotationbiochemicaland pages 68-71, ambilwade2016structuralcharacterizationofa pages 115-118) | HP0256 was proposed as FliJ; reported comparisons include 17% identity and 44% similarity to S. typhi FliJ and 33% identity and 56% similarity to C. jejuni FliJ over 142 residues (dhindwal2021annotationbiochemicalandb pages 68-71) | Low-to-moderate; definitive complementation or native-complex evidence was not found. |
| ATPase-complex stoichiometry | Canonical architecture is FliH12–FliI6–FliJ1 below the export gate. | Homolog inference | Modern flagellar export reviews, 2022–2024 (minamino2022activationmechanismof pages 12-13, ambilwade2016structuralcharacterizationof pages 40-45) | 12 FliH, 6 FliI, and 1 FliJ | High for model organisms; unverified in H. pylori, particularly because its FliJ assignment is unresolved. |
| Dual-fuel mechanism | ATP hydrolysis supports substrate docking, chaperone release or remodeling, ordered export, and gate activation; ion motive force principally drives transmembrane protein export. | Mechanistic inference from Salmonella and other homologs | Minamino et al., November 2022, DOI, with 2023–2024 reviews and studies (minamino2022activationmechanismof pages 12-13, ambilwade2016structuralcharacterizationof pages 40-45) | ATP-hydrolysis rate does not simply equal export rate; no Q9ZJJ3-specific energetic partition was measured | High as the current general fT3SS model; moderate when transferred to H. pylori. |
Table: Evidence-calibrated functional annotation of H. pylori J99 FliI/Q9ZJJ3, distinguishing direct organism-specific findings from database assignments and homolog-based mechanistic inference.
The supplied mapping—fliI / jhp_1315 / Q9ZJJ3 / H. pylori J99—is biologically coherent. The literature describes H. pylori FliI as a 434-residue, approximately 47-kDa Walker-type ATPase. Its central catalytic region contains a conserved P-loop/Walker A motif, with an N-terminal interaction region and a helical C-terminal region. It has reported sequence similarity to both Salmonella FliI and F1-ATPase catalytic subunits, explaining assignment to the ATPase alpha/beta-chain superfamily and the more specific FliI/YscN secretion-ATPase family. (ambilwade2016structuralcharacterizationof pages 35-40, ambilwade2016structuralcharacterizationofa pages 35-40)
This family relationship also resolves a potentially misleading nomenclature issue. “Flagellum-specific ATP synthase” is a historical or family-based description; FliI is not the membrane F0F1 enzyme that synthesizes cellular ATP. It is an ATP-hydrolyzing component of the flagellar export apparatus. Its homology to F1 α/β subunits reflects evolutionary and structural similarity, including a ring-forming nucleotide-binding fold, not ATP-synthase function in oxidative phosphorylation. (ambilwade2016structuralcharacterizationof pages 40-45, ambilwade2016structuralcharacterizationof pages 35-40)
The expected reaction is magnesium-dependent ATP hydrolysis:
ATP + H₂O → ADP + inorganic phosphate + H⁺.
ATP is therefore the small-molecule substrate, with Mg²⁺ serving as the physiological nucleotide-associated cofactor. Flagellar export proteins and their chaperones are functional interaction partners or cargo-delivery substrates, but they are not chemically hydrolyzed by FliI. The conserved P-loop and catalytic architecture strongly support ATPase activity. Nevertheless, no reliable Q9ZJJ3-specific Km, kcat, catalytic efficiency, or systematic ATP-versus-other-NTP selectivity panel was recovered. Accordingly, ATP specificity is high-confidence family annotation, while quantitative kinetics remain unknown for the J99 protein. (ambilwade2016structuralcharacterizationof pages 40-45, ambilwade2016structuralcharacterizationof pages 35-40, ambilwade2016structuralcharacterizationofa pages 40-45)
An E193Q variant of H. pylori FliI was purified in structural work, but low yield, precipitation, and failure to detect hexamers limited interpretation. Its theoretical mass was 47 kDa and its apparent size by size-exclusion chromatography was approximately 65 kDa. These results do not establish native oligomeric state or kinetic activity. (ambilwade2016structuralcharacterizationof pages 115-118)
Current expert models no longer describe FliI simply as a motor that directly pushes every exported polypeptide through the membrane. Instead, ATP binding and hydrolysis organize the soluble export machinery, promote substrate/chaperone docking and remodeling, contribute to ordered substrate selection, and activate the membrane export gate. The transmembrane gate then couples protein export primarily to inward ion flow—usually proton motive force, with sodium use possible in some systems. Thus, ATP and ion motive force form a dual-fuel export engine, but they perform distinguishable roles. (minamino2022activationmechanismof pages 12-13, ambilwade2016structuralcharacterizationof pages 40-45)
This mechanistic partition is best established in Salmonella, not directly in H. pylori. For Q9ZJJ3, it is a strong inference because the catalytic residues, FliH interaction, export phenotype, and wider fT3SS architecture are conserved.
FliI functions in the flagellar type III secretion system (fT3SS). This apparatus exports unfolded axial flagellar subunits from the cytoplasm through a membrane gate and then through the narrow central channel of the growing flagellum. Exported proteins build the rod, hook, hook–filament junction, filament, and cap in a regulated order.
Classic H. pylori work showed that a flagellar-specific ATPase FliI is necessary for flagellar export, directly linking the protein to flagellum assembly rather than merely to motor rotation. The relevant primary report is Jenks et al., published in 1997 in FEMS Microbiology Letters, DOI: 10.1111/j.1574-6968.1997.tb10429.x. The retrieved material confirms the export requirement but does not establish that the experimental allele was specifically the J99 jhp_1315 allele; this is therefore direct species-level evidence, not unambiguous strain-specific evidence. (tsang2015basalbodystructures pages 10-10, ambilwade2016structuralcharacterizationof pages 35-40)
Loss of productive FliI function is expected to prevent export of axial components and consequently yield defective or absent external flagella and impaired motility. These are downstream consequences of the precise molecular defect—failure of the fT3SS export pathway—not evidence that FliI is itself a filament protein or rotary-motor torque generator.
FliI also participates indirectly in the ordered transition from early rod/hook substrates to later junction, filament, and cap substrates. Recent work in Salmonella indicates that FliH and FliI help remodel the FlhA sorting platform and correct substrate-recognition errors during specificity switching. This is a current mechanistic model relevant to H. pylori, but it has not been demonstrated directly for Q9ZJJ3.
FliI is predicted and functionally inferred to be cytoplasmic and peripheral to the membrane, concentrated at the cytoplasmic face of the flagellar basal body. It is not an integral membrane protein, periplasmic enzyme, secreted flagellar subunit, or extracellular protein.
In the canonical model, FliH recruits FliI to the C ring and membrane export apparatus. FliH contacts C-ring components and FlhA while binding the N-terminal region of FliI. This places the ATPase immediately below the transmembrane export gate, where incoming chaperone–substrate complexes can be received and processed. Most high-resolution localization details come from Salmonella and related systems, while direct imaging of Q9ZJJ3 at the J99 basal body was not found. The localization should therefore be assigned moderate-to-high confidence, rather than described as directly visualized in J99. (ambilwade2016structuralcharacterizationofa pages 35-40, ambilwade2016structuralcharacterizationof pages 35-40)
FliH is the best-established H. pylori FliI partner. Direct work by Lane, O’Toole and Moore examined the molecular basis of the H. pylori FliI–FliH interaction in 2006 (Journal of Biological Chemistry; DOI: 10.1074/jbc.M507238200). The FliI N-terminal region mediates partner binding, while FliH regulates ATPase activity and recruits the complex to the export apparatus. Supporting purification work detected an approximately 75-kDa complex between FliH and FliI(E193Q), although size-exclusion chromatography could not establish its exact stoichiometry. (dhindwal2024helicobacterpyloriflgn pages 17-18, ambilwade2016structuralcharacterizationof pages 115-118)
Homolog studies suggest that soluble FliH₂–FliI units prevent unproductive ATP hydrolysis and deliver FliI to the basal body. In an assembled canonical complex, six FliI subunits associate with twelve FliH subunits. This FliH₁₂–FliI₆ arrangement is well supported in model systems but has not been measured directly in H. pylori. (ambilwade2016structuralcharacterizationofa pages 32-35, ambilwade2016structuralcharacterizationof pages 40-45)
The most important recent organism-specific advance was the January 2024 Protein Science study by Dhindwal, Boniecki and Moore (33:e4882; DOI: 10.1002/pro.4882). It identified HP1120 as the H. pylori FlgN chaperone and showed that FlgN binds its substrate FlgK with nanomolar affinity and 1:1 stoichiometry. A truncated FlgN construct also bound full-length FliI or its N-terminal domain with sub-micromolar affinity. (dhindwal2024helicobacterpyloriflgn pages 1-2)
These measurements provide direct biochemical support for a cargo-delivery model: FlgN captures the low-abundance hook–filament junction substrate FlgK and couples that complex to FliI at the export apparatus. The interaction was demonstrated in vitro; its exact timing and geometry in living H. pylori remain inferential. (dhindwal2024helicobacterpyloriflgn pages 1-2)
Canonical fT3SS ATPase complexes contain one FliJ central-stalk protein within the FliI hexamer, producing an overall FliH₁₂–FliI₆–FliJ₁ assembly. FliJ is homologous in architecture to the F1-ATPase γ subunit and promotes FliI-ring stability, FlhA activation, and chaperone recycling in model organisms. (ambilwade2016structuralcharacterizationof pages 40-45)
The corresponding H. pylori assignment is unresolved. HP0256 has been proposed as FliJ based on sequence and functional comparisons, but reported similarity varies with the comparator, and the available studies explicitly call for further confirmation. Purified HP0256 behaved as a monomer by size-exclusion chromatography. Therefore, FliJ-dependent claims should not be presented as directly established for Q9ZJJ3. (dhindwal2021annotationbiochemicalandb pages 68-71, ambilwade2016structuralcharacterizationofa pages 115-118)
Active FliI is expected to form a homohexameric ring. ATP or nonhydrolyzable ATP analogues promote ring formation in homolog systems, whereas ATP hydrolysis and release of ADP and phosphate destabilize the ring. AMP-PNP reportedly increased complete hexamer yield approximately 20-fold in a homolog study. The FliI ring resembles the catalytic ring of rotary ATPases, consistent with the supplied InterPro ATPase α/β-chain and F1/V1/A1 nucleotide-binding annotations. (ambilwade2016structuralcharacterizationof pages 40-45, ambilwade2016structuralcharacterizationofa pages 40-45)
This ring state has not been convincingly demonstrated for purified H. pylori FliI. The E193Q protein remained predominantly monomeric and did not produce detectable hexamers under the tested AMP-PNP conditions. Possible explanations include low protein concentration, instability or misfolding, the mutation itself, limitations of size-exclusion chromatography, or absence of a stabilizing partner such as FliJ. This negative result lowers confidence in assigning a constitutive hexamer to isolated Q9ZJJ3 but does not overturn the conserved in vivo assembly model. (ambilwade2016structuralcharacterizationof pages 115-118)
FliI's direct role is flagellar protein export; motility and host colonization are downstream biological consequences. In H. pylori, functional flagella enable movement through gastric mucus and are important to infection biology. FliI is consequently a plausible anti-virulence target: inhibiting its ATPase activity, oligomerization, FliH docking, or chaperone recognition could suppress flagellum assembly without targeting housekeeping F0F1 ATP synthase.
No clinical implementation, approved FliI inhibitor, or Q9ZJJ3-directed therapeutic was identified. The current real-world applications are principally experimental:
The 2024 FlgN study creates a particularly tractable assay system for testing inhibitors of the FliI N-terminal cargo-delivery interface. However, therapeutic relevance remains prospective rather than demonstrated. (dhindwal2024helicobacterpyloriflgn pages 1-2)
fliI (jhp_1315; UniProt Q9ZJJ3) encodes the approximately 47-kDa cytoplasmic flagellar-export ATPase FliI of H. pylori J99. Its conserved nucleotide-binding domain catalyzes Mg²⁺-dependent ATP hydrolysis. Through FliH and export chaperones such as FlgN, FliI is recruited to the cytoplasmic face of the flagellar basal body, where it recognizes and remodels export complexes and activates the fT3SS membrane gate. It is required for efficient export of structural flagellar substrates and thus for flagellum assembly and motility. A hexameric FliI ring and dual-fuel ATP/ion-motive-force mechanism are strongly supported by conserved homolog systems but have not been fully reconstituted or quantitatively characterized for Q9ZJJ3 itself.
References
(ambilwade2016structuralcharacterizationof pages 35-40): DP Ambilwade. Structural characterization of components of the flagellar export apparatus from the h. pylori. Unknown journal, 2016.
(ambilwade2016structuralcharacterizationofa pages 35-40): DP Ambilwade. Structural characterization of components of the flagellar export apparatus from the h. pylori. Unknown journal, 2016.
(ambilwade2016structuralcharacterizationofa pages 40-45): DP Ambilwade. Structural characterization of components of the flagellar export apparatus from the h. pylori. Unknown journal, 2016.
(ambilwade2016structuralcharacterizationof pages 40-45): DP Ambilwade. Structural characterization of components of the flagellar export apparatus from the h. pylori. Unknown journal, 2016.
(tsang2015basalbodystructures pages 10-10): Jennifer Tsang and Timothy R. Hoover. Basal body structures differentially affect transcription of rpon- and flia-dependent flagellar genes in helicobacter pylori. Journal of Bacteriology, 197:1921-1930, Jun 2015. URL: https://doi.org/10.1128/jb.02533-14, doi:10.1128/jb.02533-14. This article has 30 citations and is from a peer-reviewed journal.
(dhindwal2024helicobacterpyloriflgn pages 17-18): Poonam Dhindwal, Michal T. Boniecki, and Stanley A. Moore.
(ambilwade2016structuralcharacterizationof pages 115-118): DP Ambilwade. Structural characterization of components of the flagellar export apparatus from the h. pylori. Unknown journal, 2016.
(dhindwal2024helicobacterpyloriflgn pages 1-2): Poonam Dhindwal, Michal T. Boniecki, and Stanley A. Moore.
(dhindwal2021annotationbiochemicaland pages 68-71): P Dhindwal. Annotation, biochemical and structural analysis of the helicobacter pylori flagellum chaperone flgn in complex with its binding partners: flgk and flii. Unknown journal, 2021.
(ambilwade2016structuralcharacterizationofa pages 115-118): DP Ambilwade. Structural characterization of components of the flagellar export apparatus from the h. pylori. Unknown journal, 2016.
(dhindwal2021annotationbiochemicalandb pages 68-71): P Dhindwal. Annotation, biochemical and structural analysis of the helicobacter pylori flagellum chaperone flgn in complex with its binding partners: flgk and flii. Unknown journal, 2021.
(minamino2022activationmechanismof pages 12-13): Tohru Minamino, Miki Kinoshita, Yusuke V. Morimoto, and Keiichi Namba. Activation mechanism of the bacterial flagellar dual-fuel protein export engine. Biophysics and Physicobiology, 19:n/a, Nov 2022. URL: https://doi.org/10.2142/biophysico.bppb-v19.0046, doi:10.2142/biophysico.bppb-v19.0046. This article has 18 citations.
(ambilwade2016structuralcharacterizationofa pages 32-35): DP Ambilwade. Structural characterization of components of the flagellar export apparatus from the h. pylori. Unknown journal, 2016.