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- PDB-6xdc: Cryo-EM structure of SARS-CoV-2 ORF3a -

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Basic information

Entry
Database: PDB / ID: 6xdc
TitleCryo-EM structure of SARS-CoV-2 ORF3a
ComponentsORF3a protein
KeywordsTRANSPORT PROTEIN / SARS-CoV-2 / coronavirus / viroporin / ion channel
Function / homology
Function and homology information


host cell lysosome / induction by virus of host reticulophagy / Maturation of protein 3a / SARS-CoV-2 modulates autophagy / inorganic cation transmembrane transport / host cell endoplasmic reticulum / voltage-gated calcium channel complex / SARS-CoV-2 targets host intracellular signalling and regulatory pathways / voltage-gated potassium channel complex / molecular function activator activity ...host cell lysosome / induction by virus of host reticulophagy / Maturation of protein 3a / SARS-CoV-2 modulates autophagy / inorganic cation transmembrane transport / host cell endoplasmic reticulum / voltage-gated calcium channel complex / SARS-CoV-2 targets host intracellular signalling and regulatory pathways / voltage-gated potassium channel complex / molecular function activator activity / : / protein complex oligomerization / monoatomic ion channel activity / host cell endosome / Translation of Structural Proteins / Virion Assembly and Release / Induction of Cell-Cell Fusion / Attachment and Entry / host cell endoplasmic reticulum membrane / SARS-CoV-2 activates/modulates innate and adaptive immune responses / host cell plasma membrane / virion membrane / extracellular region / identical protein binding / plasma membrane
Similarity search - Function
Protein 3a, betacoronavirus / 3a-like viroporin, transmembrane domain, alpha/betacoronavirus / 3a-like viroporin, cytosolic domain, alpha/betacoronavirus / Betacoronavirus viroporin / Coronavirus (CoV) 3a-like viroporin trans-membrane (TM) domain profile. / Coronavirus (CoV) 3a-like viroporin cytosolic (CD) domain profile.
Similarity search - Domain/homology
Biological speciesSevere acute respiratory syndrome coronavirus 2
MethodELECTRON MICROSCOPY / single particle reconstruction / cryo EM / Resolution: 2.9 Å
AuthorsKern, D.M. / Hoel, C.M. / Brohawn, S.G.
Funding support United States, 2items
OrganizationGrant numberCountry
National Institutes of Health/National Institute of General Medical Sciences (NIH/NIGMS)GM128263 United States
National Institutes of Health/National Institute of General Medical Sciences (NIH/NIGMS)GM123496 United States
Citation
Journal: Nat Struct Mol Biol / Year: 2021
Title: Cryo-EM structure of SARS-CoV-2 ORF3a in lipid nanodiscs.
Authors: David M Kern / Ben Sorum / Sonali S Mali / Christopher M Hoel / Savitha Sridharan / Jonathan P Remis / Daniel B Toso / Abhay Kotecha / Diana M Bautista / Stephen G Brohawn /
Abstract: SARS-CoV-2 ORF3a is a putative viral ion channel implicated in autophagy inhibition, inflammasome activation and apoptosis. 3a protein and anti-3a antibodies are found in infected patient tissues and ...SARS-CoV-2 ORF3a is a putative viral ion channel implicated in autophagy inhibition, inflammasome activation and apoptosis. 3a protein and anti-3a antibodies are found in infected patient tissues and plasma. Deletion of 3a in SARS-CoV-1 reduces viral titer and morbidity in mice, suggesting it could be an effective target for vaccines or therapeutics. Here, we present structures of SARS-CoV-2 3a determined by cryo-EM to 2.1-Å resolution. 3a adopts a new fold with a polar cavity that opens to the cytosol and membrane through separate water- and lipid-filled openings. Hydrophilic grooves along outer helices could form ion-conduction paths. Using electrophysiology and fluorescent ion imaging of 3a-reconstituted liposomes, we observe Ca-permeable, nonselective cation channel activity, identify mutations that alter ion permeability and discover polycationic inhibitors of 3a activity. 3a-like proteins are found across coronavirus lineages that infect bats and humans, suggesting that 3a-targeted approaches could treat COVID-19 and other coronavirus diseases.
#1: Journal: bioRxiv / Year: 2021
Title: Cryo-EM structure of the SARS-CoV-2 3a ion channel in lipid nanodiscs.
Authors: David M Kern / Ben Sorum / Sonali S Mali / Christopher M Hoel / Savitha Sridharan / Jonathan P Remis / Daniel B Toso / Abhay Kotecha / Diana M Bautista / Stephen G Brohawn /
Abstract: Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the virus that causes the coronavirus disease 2019 (COVID-19). SARS-CoV-2 encodes three putative ion channels: E, 8a, and 3a. 3a is ...Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the virus that causes the coronavirus disease 2019 (COVID-19). SARS-CoV-2 encodes three putative ion channels: E, 8a, and 3a. 3a is expressed in SARS patient tissue and anti-3a antibodies are observed in patient plasma. 3a has been implicated in viral release, inhibition of autophagy, inflammasome activation, and cell death and its deletion reduces viral titer and morbidity in mice, raising the possibility that 3a could be an effective vaccine or therapeutic target. Here, we present the first cryo-EM structures of SARS-CoV-2 3a to 2.1 Å resolution and demonstrate 3a forms an ion channel in reconstituted liposomes. The structures in lipid nanodiscs reveal 3a dimers and tetramers adopt a novel fold with a large polar cavity that spans halfway across the membrane and is accessible to the cytosol and the surrounding bilayer through separate water- and lipid-filled openings. Electrophysiology and fluorescent ion imaging experiments show 3a forms Ca-permeable non-selective cation channels. We identify point mutations that alter ion permeability and discover polycationic inhibitors of 3a channel activity. We find 3a-like proteins in multiple and lineages that infect bats and humans. These data show 3a forms a functional ion channel that may promote COVID-19 pathogenesis and suggest targeting 3a could broadly treat coronavirus diseases.
History
DepositionJun 10, 2020Deposition site: RCSB / Processing site: RCSB
Revision 1.0Jun 17, 2020Provider: repository / Type: Initial release
Revision 1.1Jul 8, 2020Group: Database references / Category: citation / citation_author
Item: _citation.country / _citation.journal_abbrev ..._citation.country / _citation.journal_abbrev / _citation.journal_id_CSD / _citation.pdbx_database_id_DOI / _citation.pdbx_database_id_PubMed / _citation.title / _citation.year
Revision 1.2Jan 27, 2021Group: Structure summary / Category: entity / entity_name_com / Item: _entity.pdbx_description / _entity_name_com.name
Revision 1.3Aug 18, 2021Group: Database references / Category: citation / citation_author / database_2
Item: _citation.year / _database_2.pdbx_DOI / _database_2.pdbx_database_accession
Revision 1.4Aug 31, 2022Group: Database references / Category: citation / citation_author

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Structure visualization

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  • EMDB-22136
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Structure viewerMolecule:
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Assembly

Deposited unit
A: ORF3a protein
B: ORF3a protein


Theoretical massNumber of molelcules
Total (without water)64,3322
Polymers64,3322
Non-polymers00
Water0
1


  • Idetical with deposited unit
  • defined by author
  • Evidence: gel filtration
TypeNameSymmetry operationNumber
identity operation1_5551
Buried area5110 Å2
ΔGint-45 kcal/mol
Surface area19840 Å2

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Components

#1: Protein ORF3a protein / Accessory protein 3a / Protein U274 / Protein X1 / ORF3a / Protein 3a


Mass: 32165.902 Da / Num. of mol.: 2
Source method: isolated from a genetically manipulated source
Source: (gene. exp.) Severe acute respiratory syndrome coronavirus 2
Gene: 3a / Production host: Spodoptera frugiperda (fall armyworm) / References: UniProt: P0DTC3

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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: ORF3a in MSPE3D1 nanodisc / Type: COMPLEX / Entity ID: all / Source: RECOMBINANT
Molecular weightValue: 0.064 MDa / Experimental value: NO
Source (natural)Organism: Severe acute respiratory syndrome coronavirus 2
Source (recombinant)Organism: Spodoptera frugiperda (fall armyworm)
Buffer solutionpH: 7.4
Buffer component
IDConc.NameFormulaBuffer-ID
120 mMHEPES1
2150 mMpotassium chlorideKCl1
SpecimenConc.: 1.1 mg/ml / Embedding applied: NO / Shadowing applied: NO / Staining applied: NO / Vitrification applied: YES
Specimen supportGrid material: GOLD / Grid mesh size: 300 divisions/in. / Grid type: Quantifoil
VitrificationInstrument: FEI VITROBOT MARK IV / Cryogen name: ETHANE / Humidity: 100 % / Chamber temperature: 277 K
Details: 1 blot force, 5 second wait time, 3 second blot time

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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 FIELDBright-field microscopy / 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: 5 sec. / Electron dose: 50.675 e/Å2 / Film or detector model: GATAN K3 (6k x 4k) / Num. of grids imaged: 1 / Num. of real images: 2595 / Details: 50 frames per image
Image scansWidth: 11520 / Height: 8184

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Processing

Software
NameVersionClassification
phenix.real_space_refine1.17.1_3660refinement
PHENIX1.17.1_3660refinement
EM software
IDNameVersionCategory
1Topazparticle selection
4CTFFIND4.1CTF correction
7Coot0.9-premodel fitting
9cryoSPARC2initial Euler assignment
10cryoSPARC2final Euler assignment
11cryoSPARCclassification
12cryoSPARC23D reconstruction
13PHENIX1.17.1-3660model refinement
CTF correctionType: PHASE FLIPPING AND AMPLITUDE CORRECTION
Particle selectionNum. of particles selected: 4134279
SymmetryPoint symmetry: C2 (2 fold cyclic)
3D reconstructionResolution: 2.9 Å / Resolution method: FSC 0.143 CUT-OFF / Num. of particles: 185871 / Symmetry type: POINT
Atomic model buildingB value: 108.61 / Protocol: OTHER / Space: REAL
RefinementCross valid method: NONE
Stereochemistry target values: GeoStd + Monomer Library + CDL v1.2
Displacement parametersBiso mean: 108.61 Å2
Refine LS restraints
Refine-IDTypeDev idealNumber
ELECTRON MICROSCOPYf_bond_d0.00593244
ELECTRON MICROSCOPYf_angle_d0.78324424
ELECTRON MICROSCOPYf_chiral_restr0.0619502
ELECTRON MICROSCOPYf_plane_restr0.0077528
ELECTRON MICROSCOPYf_dihedral_angle_d18.00911098

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