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- PDB-9wi0: cryo-EM structure of E.coli ArnA -

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Basic information

Entry
Database: PDB / ID: 9wi0
Titlecryo-EM structure of E.coli ArnA
ComponentsBifunctional polymyxin resistance protein ArnA
KeywordsANTIBIOTIC / Bifunctional polymyxin resistance protein ArnA
Function / homology
Function and homology information


UDP-4-deoxy-4-formamido-beta-L-arabinopyranose biosynthetic process / UDP-glucuronate dehydrogenase activity / UDP-4-amino-4-deoxy-L-arabinose formyltransferase activity / UDP-glucuronic acid dehydrogenase (UDP-4-keto-hexauronic acid decarboxylating) / UDP-4-amino-4-deoxy-L-arabinose formyltransferase / UDP-D-xylose biosynthetic process / UDP-glucuronate decarboxylase activity / lipopolysaccharide biosynthetic process / lipid A biosynthetic process / NAD+ binding ...UDP-4-deoxy-4-formamido-beta-L-arabinopyranose biosynthetic process / UDP-glucuronate dehydrogenase activity / UDP-4-amino-4-deoxy-L-arabinose formyltransferase activity / UDP-glucuronic acid dehydrogenase (UDP-4-keto-hexauronic acid decarboxylating) / UDP-4-amino-4-deoxy-L-arabinose formyltransferase / UDP-D-xylose biosynthetic process / UDP-glucuronate decarboxylase activity / lipopolysaccharide biosynthetic process / lipid A biosynthetic process / NAD+ binding / response to antibiotic / protein-containing complex / identical protein binding / membrane
Similarity search - Function
Bifunctional polymyxin resistance protein, ArnA / Bifunctional polymyxin resistance protein ArnA-like, extended (e) SDRs / : / Formyl transferase, C-terminal / Formyl transferase, C-terminal domain / Formyl transferase-like, C-terminal domain superfamily / Formyl transferase, N-terminal / Formyl transferase / Formyl transferase, N-terminal domain superfamily / NAD-dependent epimerase/dehydratase ...Bifunctional polymyxin resistance protein, ArnA / Bifunctional polymyxin resistance protein ArnA-like, extended (e) SDRs / : / Formyl transferase, C-terminal / Formyl transferase, C-terminal domain / Formyl transferase-like, C-terminal domain superfamily / Formyl transferase, N-terminal / Formyl transferase / Formyl transferase, N-terminal domain superfamily / NAD-dependent epimerase/dehydratase / NAD dependent epimerase/dehydratase family / NAD(P)-binding domain superfamily
Similarity search - Domain/homology
Bifunctional polymyxin resistance protein ArnA
Similarity search - Component
Biological speciesEscherichia coli BW25113 (bacteria)
MethodELECTRON MICROSCOPY / single particle reconstruction / cryo EM / Resolution: 2.89 Å
AuthorsLiu, X. / Li, J.
Funding support China, 1items
OrganizationGrant numberCountry
Other government23700-52531020 China
CitationJournal: Biomolecules / Year: 2025
Title: Structural Basis for Targeting the Bifunctional Enzyme ArnA.
Authors: Xinyu Liu / Ruochen Yang / Libang Ren / Tong Li / Yanrong Li / Zhihua Yan / Yanrong Gao / Mingqi Yang / Jiazhi Li /
Abstract: Polymyxin antibiotics are often the last line of defense against multidrug-resistant Gram-negative pathogens. A key resistance mechanism involves the addition of 4-amino-4-deoxy-L-arabinose (L-Ara4N) ...Polymyxin antibiotics are often the last line of defense against multidrug-resistant Gram-negative pathogens. A key resistance mechanism involves the addition of 4-amino-4-deoxy-L-arabinose (L-Ara4N) to lipid A, mediated by the bifunctional enzyme ArnA. However, the evolutionary rationale and structural basis for ArnA's domain fusion, hexameric assembly, and catalytic coordination remain mechanistically unresolved. Here, we integrate evolutionary genomics, high-resolution cryo-electron microscopy (cryo-EM), and computational protein design to provide a comprehensive mechanistic analysis of ArnA. Our evolutionary analysis reveals that the dehydrogenase (DH) and formyltransferase (TF) domains evolved independently and were selectively fused in Gammaproteobacteria, suggesting an adaptive advantage. A 2.89 Å cryo-EM structure of apo-ArnA resolves the flexible interdomain linker and reveals a DH-driven hexameric architecture essential for enzymatic activity. 3D variability analysis captures intrinsic conformational dynamics, indicating a molecular switch that may coordinate sequential catalysis and substrate channeling. Structure-based peptide inhibitors targeting the hexamerization and predicted ArnA-ArnB interaction interfaces were computationally designed, offering a novel strategy for disrupting L-Ara4N biosynthesis. These findings illuminate a previously uncharacterized structural mechanism of antimicrobial resistance and lay the groundwork for therapeutic intervention.
History
DepositionAug 27, 2025Deposition site: PDBJ / Processing site: PDBC
Revision 1.0Nov 26, 2025Provider: repository / Type: Initial release
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Revision 1.1Dec 10, 2025Group: Data collection / Database references / Category: citation / em_admin
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Structure visualization

Structure viewerMolecule:
MolmilJmol/JSmol

Downloads & links

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Assembly

Deposited unit
A: Bifunctional polymyxin resistance protein ArnA
B: Bifunctional polymyxin resistance protein ArnA
C: Bifunctional polymyxin resistance protein ArnA
D: Bifunctional polymyxin resistance protein ArnA
E: Bifunctional polymyxin resistance protein ArnA
F: Bifunctional polymyxin resistance protein ArnA


Theoretical massNumber of molelcules
Total (without water)446,3156
Polymers446,3156
Non-polymers00
Water00
1


  • Idetical with deposited unit
  • defined by author
  • Evidence: electron microscopy, not applicable
TypeNameSymmetry operationNumber
identity operation1_5551

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Components

#1: Protein
Bifunctional polymyxin resistance protein ArnA / Polymyxin resistance protein PmrI


Mass: 74385.773 Da / Num. of mol.: 6
Source method: isolated from a genetically manipulated source
Details: Sequence reference for Escherichia coli BW25113 is not available at the time of biocuration. Current sequence reference is from UniProt ID P77398.
Source: (gene. exp.) Escherichia coli BW25113 (bacteria) / Production host: Escherichia coli BL21(DE3) (bacteria)
References: UniProt: P77398, UDP-4-amino-4-deoxy-L-arabinose formyltransferase, UDP-glucuronic acid dehydrogenase (UDP-4-keto-hexauronic acid decarboxylating)
Has protein modificationY

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Experimental details

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Experiment

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

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Sample preparation

ComponentName: Bifunctional polymyxin resistance protein ArnA / Type: CELL / Entity ID: all / Source: RECOMBINANT
Source (natural)Organism: Escherichia coli BW25113 (bacteria)
Source (recombinant)Organism: Escherichia coli BL21(DE3) (bacteria)
Buffer solutionpH: 7.5
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: 1800 nm / Nominal defocus min: 1100 nm
Image recordingElectron dose: 60 e/Å2 / Film or detector model: GATAN K2 QUANTUM (4k x 4k) / Num. of grids imaged: 1 / Num. of real images: 6563

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Processing

EM software
IDNameCategory
1cryoSPARCparticle selection
13cryoSPARC3D reconstruction
CTF correctionType: PHASE FLIPPING AND AMPLITUDE CORRECTION
3D reconstructionResolution: 2.89 Å / Resolution method: FSC 0.143 CUT-OFF / Num. of particles: 476403 / Symmetry type: POINT
RefinementHighest resolution: 2.89 Å
Stereochemistry target values: REAL-SPACE (WEIGHTED MAP SUM AT ATOM CENTERS)
Refine LS restraints
Refine-IDTypeDev idealNumber
ELECTRON MICROSCOPYf_bond_d0.00232070
ELECTRON MICROSCOPYf_angle_d0.56543548
ELECTRON MICROSCOPYf_dihedral_angle_d5.274361
ELECTRON MICROSCOPYf_chiral_restr0.0424752
ELECTRON MICROSCOPYf_plane_restr0.0055682

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