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- PDB-9d26: A widespread heme dechelatase in healthy and pathogenic human mic... -

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Entry
Database: PDB / ID: 9d26
TitleA widespread heme dechelatase in healthy and pathogenic human microbiomes.
ComponentsHmuS heme dechelatase
KeywordsMETAL TRANSPORT / Iron / Microbiome / Heme
Function / homologycobaltochelatase activity / CobN/magnesium chelatase / CobN/Magnesium Chelatase / membrane / PROTOPORPHYRIN IX CONTAINING FE / Cobaltochelatase subunit CobN
Function and homology information
Biological speciesBacteroides (bacteria)
MethodELECTRON MICROSCOPY / single particle reconstruction / cryo EM / Resolution: 2.6 Å
AuthorsGauvin, C.C. / Nath, A.K. / Rodrigues da Silva, R. / Akpoto, E. / Dubois, J.L. / Lawrence, C.M.
Funding support United States, 3items
OrganizationGrant numberCountry
National Institutes of Health/National Institute of General Medical Sciences (NIH/NIGMS) United States
National Science Foundation (NSF, United States)DBI-1828765 United States
National Institutes of Health/National Institute of General Medical Sciences (NIH/NIGMS)P30GM140963 United States
Citation
Journal: EMBO J / Year: 2025
Title: Commensal gut bacteria employ de-chelatase HmuS to harvest iron from heme.
Authors: Arnab Kumar Nath / Ronivaldo Rodrigues da Silva / Colin C Gauvin / Emmanuel Akpoto / Mensur Dlakić / C Martin Lawrence / Jennifer L DuBois /
Abstract: Iron is essential for almost all organisms, which have evolved different strategies for ensuring a sufficient supply from their environment and using it in different forms, including heme. The hmu ...Iron is essential for almost all organisms, which have evolved different strategies for ensuring a sufficient supply from their environment and using it in different forms, including heme. The hmu operon, primarily found in Bacteroidota and ubiquitous in gastrointestinal tract metagenomes of healthy humans, encodes proteins involved in heme acquisition. Here, we provide direct physiological, biochemical, and structural evidence for the anaerobic removal of iron from heme by HmuS, a membrane-bound, NADH-dependent de-chelatase that deconstructs heme to protoporphyrin IX (PPIX) and Fe(II). Heme can serve as the sole iron source for the model gastrointestinal bacterium Bacteroidetes thetaiotaomicron, when active HmuS is present. Heterologously expressed HmuS was isolated with bound heme molecules under saturating conditions. Its cryo-EM structure at 2.6 Å resolution revealed binding of heme and a pair of cations at distant sites. These sites are conserved across the HmuS family and chelatase superfamily, respectively. The proposed structure-based mechanism for iron removal by HmuS is chemically analogous to the chelatases in both unrelated heme biosynthetic pathways and homologous enzymes in the biosynthetic pathways for chlorophyll and vitamin B12, although the reaction proceeds in the opposite direction. Taken together, our study identifies a widespread mechanism via which anaerobic bacteria can extract nutritional iron from heme.
#1: Journal: Acta Crystallogr D Struct Biol / Year: 2019
Title: Macromolecular structure determination using X-rays, neutrons and electrons: recent developments in Phenix.
Authors: Dorothee Liebschner / Pavel V Afonine / Matthew L Baker / Gábor Bunkóczi / Vincent B Chen / Tristan I Croll / Bradley Hintze / Li Wei Hung / Swati Jain / Airlie J McCoy / Nigel W Moriarty ...Authors: Dorothee Liebschner / Pavel V Afonine / Matthew L Baker / Gábor Bunkóczi / Vincent B Chen / Tristan I Croll / Bradley Hintze / Li Wei Hung / Swati Jain / Airlie J McCoy / Nigel W Moriarty / Robert D Oeffner / Billy K Poon / Michael G Prisant / Randy J Read / Jane S Richardson / David C Richardson / Massimo D Sammito / Oleg V Sobolev / Duncan H Stockwell / Thomas C Terwilliger / Alexandre G Urzhumtsev / Lizbeth L Videau / Christopher J Williams / Paul D Adams /
Abstract: Diffraction (X-ray, neutron and electron) and electron cryo-microscopy are powerful methods to determine three-dimensional macromolecular structures, which are required to understand biological ...Diffraction (X-ray, neutron and electron) and electron cryo-microscopy are powerful methods to determine three-dimensional macromolecular structures, which are required to understand biological processes and to develop new therapeutics against diseases. The overall structure-solution workflow is similar for these techniques, but nuances exist because the properties of the reduced experimental data are different. Software tools for structure determination should therefore be tailored for each method. Phenix is a comprehensive software package for macromolecular structure determination that handles data from any of these techniques. Tasks performed with Phenix include data-quality assessment, map improvement, model building, the validation/rebuilding/refinement cycle and deposition. Each tool caters to the type of experimental data. The design of Phenix emphasizes the automation of procedures, where possible, to minimize repetitive and time-consuming manual tasks, while default parameters are chosen to encourage best practice. A graphical user interface provides access to many command-line features of Phenix and streamlines the transition between programs, project tracking and re-running of previous tasks.
History
DepositionAug 8, 2024Deposition site: RCSB / Processing site: RCSB
Revision 1.0Aug 20, 2025Provider: repository / Type: Initial release
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Revision 1.0Aug 20, 2025Data content type: FSC / Data content type: FSC / Provider: repository / Type: Initial release
Revision 1.0Aug 20, 2025Data content type: Half map / Part number: 1 / Data content type: Half map / Provider: repository / Type: Initial release
Revision 1.0Aug 20, 2025Data content type: Half map / Part number: 2 / Data content type: Half map / Provider: repository / Type: Initial release
Revision 1.0Aug 20, 2025Data content type: Image / Data content type: Image / Provider: repository / Type: Initial release
Revision 1.0Aug 20, 2025Data content type: Mask / Part number: 1 / Data content type: Mask / Provider: repository / Type: Initial release
Revision 1.0Aug 20, 2025Data content type: Primary map / Data content type: Primary map / Provider: repository / Type: Initial release
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Structure visualization

Structure viewerMolecule:
MolmilJmol/JSmol

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Assembly

Deposited unit
A: HmuS heme dechelatase
hetero molecules


Theoretical massNumber of molelcules
Total (without water)163,0864
Polymers162,4231
Non-polymers6623
Water1,71195
1


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

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Components

#1: Protein HmuS heme dechelatase / Cobaltochelatase subunit CobN


Mass: 162423.281 Da / Num. of mol.: 1
Source method: isolated from a genetically manipulated source
Details: Isolated from human feces / Source: (gene. exp.) Bacteroides (bacteria) / Strain: VPI-5482
Gene: cobN, ERS852430_03305, FIB20_18370, GAN91_17490, GAO51_10745
Details (production host): T7 lac promoter driven expression vector encoding kanamycin resistance enzyme. Epitope tags were excised from the plasmid and tagless protein was expressed.
Production host: Escherichia coli BL21(DE3) (bacteria) / Variant (production host): Lemo21 (DE3) / References: UniProt: A0A0P0FP54, cobaltochelatase
#2: Chemical ChemComp-HEM / PROTOPORPHYRIN IX CONTAINING FE / HEME


Mass: 616.487 Da / Num. of mol.: 1 / Source method: obtained synthetically / Formula: C34H32FeN4O4
#3: Chemical ChemComp-NA / SODIUM ION


Mass: 22.990 Da / Num. of mol.: 2 / Source method: obtained synthetically / Formula: Na
#4: Water ChemComp-HOH / water


Mass: 18.015 Da / Num. of mol.: 95 / Source method: isolated from a natural source / Formula: H2O
Has ligand of interestN
Has protein modificationY

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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: HmuS in complex with heme / Type: COMPLEX / Entity ID: #1 / Source: RECOMBINANT
Molecular weightValue: 0.153058 MDa / Experimental value: NO
Source (natural)Organism: Bacteroides thetaiotaomicron (bacteria)
Source (recombinant)Organism: Escherichia coli (E. coli)
Buffer solutionpH: 7.1
Buffer component
IDConc.NameFormulaBuffer-ID
120 mMTris-ClC4H11NO3Cl1
2250 mMSodium ChlorideNaCl1
SpecimenConc.: 1.5 mg/ml / Embedding applied: NO / Shadowing applied: NO / Staining applied: NO / Vitrification applied: YES
Specimen supportGrid material: COPPER / Grid mesh size: 300 divisions/in. / Grid type: Quantifoil R1.2/1.3
VitrificationInstrument: FEI VITROBOT MARK IV / Cryogen name: ETHANE / Humidity: 95 % / Chamber temperature: 277 K

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Electron microscopy imaging

Experimental equipment
Model: Talos Arctica / Image courtesy: FEI Company
MicroscopyModel: FEI TALOS ARCTICA
Electron gunElectron source: FIELD EMISSION GUN / Accelerating voltage: 200 kV / Illumination mode: FLOOD BEAM
Electron lensMode: BRIGHT FIELD / Nominal magnification: 45000 X / Calibrated magnification: 55187 X / Nominal defocus max: 1500 nm / Nominal defocus min: 600 nm / Cs: 2.7 mm / C2 aperture diameter: 50 µm / Alignment procedure: COMA FREE
Specimen holderCryogen: NITROGEN / Specimen holder model: FEI TITAN KRIOS AUTOGRID HOLDER
Image recordingAverage exposure time: 3.06 sec. / Electron dose: 56 e/Å2 / Film or detector model: GATAN K3 (6k x 4k) / Num. of grids imaged: 1 / Num. of real images: 12602

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Processing

Software
NameVersionClassification
phenix.real_space_refine1.20.1_4487refinement
PHENIX1.20.1_4487refinement
EM software
IDNameVersionCategory
1cryoSPARC4particle selection
2SerialEMimage acquisition
4cryoSPARC4CTF correction
7PHENIX1.20.1model fitting
9cryoSPARC4initial Euler assignment
10cryoSPARC4final Euler assignment
11cryoSPARC4classification
12cryoSPARC43D reconstruction
13PHENIX1.20.1model refinement
CTF correctionType: PHASE FLIPPING ONLY
Particle selectionNum. of particles selected: 18955798 / Details: Blob picked, then particles washed to give
SymmetryPoint symmetry: C1 (asymmetric)
3D reconstructionResolution: 2.6 Å / Resolution method: FSC 0.143 CUT-OFF / Num. of particles: 2133842 / Algorithm: BACK PROJECTION / Symmetry type: POINT
Atomic model buildingSpace: REAL
Atomic model buildingSource name: AlphaFold / Type: in silico model
RefinementCross valid method: NONE
Stereochemistry target values: GeoStd + Monomer Library + CDL v1.2
Displacement parametersBiso mean: 127.79 Å2
Refine LS restraints
Refine-IDTypeDev idealNumber
ELECTRON MICROSCOPYf_bond_d0.002510100
ELECTRON MICROSCOPYf_angle_d0.409913685
ELECTRON MICROSCOPYf_chiral_restr0.03921485
ELECTRON MICROSCOPYf_plane_restr0.00381795
ELECTRON MICROSCOPYf_dihedral_angle_d11.75843773

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