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- PDB-36hw: Salmonella Flagellar Export Apparatus FlhA transmembrane domain n... -

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Basic information

Entry
Database: PDB / ID: 36hw
TitleSalmonella Flagellar Export Apparatus FlhA transmembrane domain nonamer in the context of the intact basal body
ComponentsFlagellar biosynthesis protein FlhA
KeywordsPROTEIN TRANSPORT / Flagella / Secretion / PMF
Function / homology
Function and homology information


protein secretion / bacterial-type flagellum assembly / plasma membrane
Similarity search - Function
Flagellar biosynthesis protein FlhA / FHIPEP, domain 1 / FHIPEP conserved site / Bacterial export FHIPEP family signature. / Type III secretion system FHIPEP / FHIPEP, domain 3 / FHIPEP, domain 4 / FHIPEP family
Similarity search - Domain/homology
Flagellar biosynthesis protein FlhA
Similarity search - Component
Biological speciesSalmonella enterica subsp. enterica serovar Typhimurium (bacteria)
MethodELECTRON MICROSCOPY / single particle reconstruction / cryo EM / Resolution: 3.55 Å
AuthorsJohnson, S. / Johnson, M.K. / Lea, S.M.
Funding support United States, 1items
OrganizationGrant numberCountry
National Institutes of Health/National Cancer Institute (NIH/NCI) United States
CitationJournal: bioRxiv / Year: 2026
Title: Structure of the proton-powered secretion motor at the heart of the bacterial flagellum.
Authors: Mary K Johnson / Steven Johnson / Justin C Deme / Luz Alfaro-Alvarado / Owain J Bryant / Fabienne F V Chevance / Kelly T Hughes / Susan M Lea /
Abstract: Bacterial type III secretion systems export proteins across the inner membrane using the proton-motive force (PMF), but how proton flow is coupled to opening of the export channel is unknown. Here we ...Bacterial type III secretion systems export proteins across the inner membrane using the proton-motive force (PMF), but how proton flow is coupled to opening of the export channel is unknown. Here we present single-particle cryo-EM structures at 2.5-4.2 Å resolution of the intact flagellar Export Apparatus from , obtained using optimized extraction conditions of the endogenous assembly that retain the complete transmembrane complex. The transmembrane domain of FlhA forms a nonameric funnel-shaped basket beneath the Export Gate, with each subunit harboring a buried pathway of conserved hydrophilic residues spanning the hydrophobic core of the membrane. FlhB is resolved for the first time within the intact gate, revealing helices that thread through the FlhA channel, completely sealing it at rest. A symmetry-free reconstruction captures one FlhA protomer hinged outward at the water-filled cavity, breaking the rotational symmetry. Together, these structures define the architecture of the proton-transducing element of the type III secretion system and suggest a rotary gating mechanism, with parallels to the F motor of ATP synthase, in which PMF-driven conformational cycling of FlhA drives regulated opening of the export channel.
History
DepositionJun 10, 2026Deposition site: RCSB / Processing site: RCSB
Revision 1.0Jul 15, 2026Provider: repository / Type: Initial release
Revision 1.0Jul 15, 2026Data content type: EM metadata / Data content type: EM metadata / Provider: repository / Type: Initial release
Revision 1.0Jul 15, 2026Data content type: Additional map / Part number: 1 / Data content type: Additional map / Provider: repository / Type: Initial release
Revision 1.0Jul 15, 2026Data content type: FSC / Data content type: FSC / Provider: repository / Type: Initial release
Revision 1.0Jul 15, 2026Data content type: Half map / Part number: 1 / Data content type: Half map / Provider: repository / Type: Initial release
Revision 1.0Jul 15, 2026Data content type: Half map / Part number: 2 / Data content type: Half map / Provider: repository / Type: Initial release
Revision 1.0Jul 15, 2026Data content type: Image / Data content type: Image / Provider: repository / Type: Initial release
Revision 1.0Jul 15, 2026Data content type: Primary map / Data content type: Primary map / Provider: repository / Type: Initial release

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Structure visualization

Structure viewerMolecule:
MolmilJmol/JSmol

Downloads & links

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Assembly

Deposited unit
A2: Flagellar biosynthesis protein FlhA
B2: Flagellar biosynthesis protein FlhA
C2: Flagellar biosynthesis protein FlhA
D2: Flagellar biosynthesis protein FlhA
E2: Flagellar biosynthesis protein FlhA
F2: Flagellar biosynthesis protein FlhA
G2: Flagellar biosynthesis protein FlhA
H2: Flagellar biosynthesis protein FlhA
I2: Flagellar biosynthesis protein FlhA


Theoretical massNumber of molelcules
Total (without water)674,2219
Polymers674,2219
Non-polymers00
Water00
1


  • Idetical with deposited unit
  • defined by author&software
  • Evidence: electron microscopy, not applicable
TypeNameSymmetry operationNumber
identity operation1_555x,y,z1

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Components

#1: Protein
Flagellar biosynthesis protein FlhA


Mass: 74913.484 Da / Num. of mol.: 9 / Source method: isolated from a natural source
Source: (natural) Salmonella enterica subsp. enterica serovar Typhimurium (bacteria)
References: UniProt: P40729
Has protein modificationN

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Experimental details

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Experiment

ExperimentMethod: ELECTRON MICROSCOPY
EM experimentAggregation state: PARTICLE / 3D reconstruction method: single particle reconstruction

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Sample preparation

ComponentName: Focussed refinement of the FlhA transmembrane domain from the intact Salmonella Flagellar Basal Body
Type: COMPLEX / Entity ID: all / Source: NATURAL
Molecular weightExperimental value: NO
Source (natural)Organism: Salmonella enterica subsp. enterica serovar Typhimurium (bacteria)
Buffer solutionpH: 8
SpecimenEmbedding applied: NO / Shadowing applied: NO / Staining applied: NO / Vitrification applied: YES
VitrificationCryogen name: ETHANE

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Electron microscopy imaging

Experimental equipment
Model: Titan Krios / Image courtesy: FEI Company
MicroscopyModel: TFS KRIOS
Electron gunElectron source: FIELD EMISSION GUN / Accelerating voltage: 300 kV / Illumination mode: FLOOD BEAM
Electron lensMode: BRIGHT FIELD / Nominal defocus max: 2500 nm / Nominal defocus min: 500 nm
Image recordingElectron dose: 58.5 e/Å2 / Film or detector model: TFS FALCON 4i (4k x 4k)

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Processing

EM software
IDNameVersionCategory
1SIMPLE3particle selection
2PHENIX2.0_5936model refinement
13cryoSPARC3D reconstruction
CTF correctionType: PHASE FLIPPING AND AMPLITUDE CORRECTION
SymmetryPoint symmetry: C9 (9 fold cyclic)
3D reconstructionResolution: 3.55 Å / Resolution method: FSC 0.143 CUT-OFF / Num. of particles: 19350 / Symmetry type: POINT
RefinementCross valid method: NONE

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