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- PDB-12if: Cryo-EM structure of B/Phuket/3037/2013 hemagglutinin trimer in c... -

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Basic information

Entry
Database: PDB / ID: 12if
TitleCryo-EM structure of B/Phuket/3037/2013 hemagglutinin trimer in complex with two KL-BHA-3D7 Fab fragments
Components
  • Hemagglutinin
  • KL-BHA-3D7 heavy chain
  • KL-BHA-3D7 light chain
KeywordsViral protein/Immune System / hemagglutinin / Fab / viral glycoprotein / Viral protein-Immune System complex
Function / homology
Function and homology information


viral budding from plasma membrane / host cell surface receptor binding / endocytosis involved in viral entry into host cell / fusion of virus membrane with host plasma membrane / fusion of virus membrane with host endosome membrane / viral envelope / virion attachment to host cell / host cell plasma membrane / virion membrane / membrane
Similarity search - Function
Haemagglutinin, influenzavirus B / Haemagglutinin, HA1 chain, alpha/beta domain superfamily / Haemagglutinin / Haemagglutinin, influenzavirus A/B / Viral capsid/haemagglutinin protein
Similarity search - Domain/homology
Biological speciesInfluenza B virus
Mus musculus (house mouse)
MethodELECTRON MICROSCOPY / single particle reconstruction / cryo EM / Resolution: 3.98 Å
AuthorsCivljak, A. / Bonnettaz, B. / Bajic, G.
Funding support United States, 5items
OrganizationGrant numberCountry
National Institutes of Health/National Institute Of Allergy and Infectious Diseases (NIH/NIAID)AI117287 United States
National Institutes of Health/National Institute Of Allergy and Infectious Diseases (NIH/NIAID)AI109946 United States
National Institutes of Health/National Institute Of Allergy and Infectious Diseases (NIH/NIAID)AI097092 United States
National Institutes of Health/National Institute Of Allergy and Infectious Diseases (NIH/NIAID)HHSN272201400008C United States
Other private United States
CitationJournal: J Virol / Year: 2026
Title: Broadly reactive antibodies against influenza B virus hemagglutinin neutralize and protect through distinct structural mechanisms.
Authors: Disha Bhavsar / Alesandro Civljak / Bruno Bonnettaz / Guha Asthagiri Arunkumar / Florian Krammer / Goran Bajic /
Abstract: Influenza B viruses contribute substantially to seasonal disease burden; however, the structural basis by which antibodies recognize the major glycoprotein hemagglutinin (HA) and mediate antiviral ...Influenza B viruses contribute substantially to seasonal disease burden; however, the structural basis by which antibodies recognize the major glycoprotein hemagglutinin (HA) and mediate antiviral activity remains incompletely defined. Influenza B virus used to circulate as two antigenically distinct lineages, B/Victoria/2/1987-like and B/Yamagata/16/1988-like, although the latter has not been detected in global surveillance in recent years. Antigenic drift in HA contributes to reduced vaccine effectiveness; however, the structural and functional basis by which antibodies recognize influenza B virus HA and mediate antiviral activity remains incompletely defined and thus thwarts our efforts in guiding next-generation vaccine design for broad protection. We characterize four murine monoclonal antibodies (mAb) that broadly bind and neutralize influenza B viruses spanning isolates across four decades of antigenic drift. Using cryo-electron microscopy coupled with and functional assays, we show that these antibodies target distinct regions of HA and confer antiviral activity through multiple mechanisms. One antibody engages the receptor-binding site and potently inhibits hemagglutination, whereas others interfere with viral egress and inhibit neuraminidase (NA) activity, suggesting steric occlusion of NA. A medial-junction antibody additionally induces antibody-dependent cellular cytotoxicity . Despite these mechanistic differences, all antibodies confer complete protection in mice when administered prophylactically or therapeutically. Together, these findings define distinct modes of antibody recognition of influenza B virus HA and link epitope specificity to antiviral function, providing a mechanistic understanding of correlates of immune protection and informing efforts to elicit broadly protective antibody responses against influenza B viruses.IMPORTANCEInfluenza B viruses cause substantial seasonal illness, particularly in children; however, antibody responses against influenza B virus remain less well understood than those against influenza A virus. Here, we identified four antibodies that broadly recognize influenza B virus hemagglutinin and protect through distinct mechanisms. We determined cryo-electron microscopy structures of three antibody-hemagglutinin complexes to define their epitopes and explain their molecular mechanisms of action. One antibody blocks viral attachment by engaging the receptor-binding site, whereas antibodies targeting the medial junction act through post-entry antiviral activity, neuraminidase inhibition, or immune effector functions. Although the antibodies differed in neutralizing potency, all protected mice when administered before infection, and several remained effective after infection. These findings show that broad protection against influenza B virus can arise through multiple antibody targets and mechanisms, informing the evaluation and design of future vaccines and antibody-based therapies.
History
DepositionApr 7, 2026Deposition site: RCSB / Processing site: RCSB
Revision 1.0Aug 26, 2026Provider: repository / Type: Initial release
Revision 1.0Aug 26, 2026Data content type: EM metadata / Data content type: EM metadata / Provider: repository / Type: Initial release
Revision 1.1Sep 16, 2026Group: Data collection / Database references / Category: citation / citation_author / em_admin
Item: _citation.country / _citation.journal_abbrev ..._citation.country / _citation.journal_abbrev / _citation.journal_id_ASTM / _citation.journal_id_CSD / _citation.journal_id_ISSN / _citation.page_first / _citation.page_last / _citation.pdbx_database_id_DOI / _citation.pdbx_database_id_PubMed / _citation.title / _citation.year / _em_admin.last_update
Revision 1.1Sep 16, 2026Data content type: EM metadata / Data content type: EM metadata / EM metadata / Group: Database references / Experimental summary / Data content type: EM metadata / EM metadata / EM metadata / Category: citation / citation_author / em_admin
Data content type: EM metadata / EM metadata ...EM metadata / EM metadata / EM metadata / EM metadata / EM metadata / EM metadata / EM metadata / EM metadata / EM metadata / EM metadata / EM metadata / EM metadata
Item: _citation.country / _citation.journal_abbrev ..._citation.country / _citation.journal_abbrev / _citation.journal_id_ASTM / _citation.journal_id_CSD / _citation.journal_id_ISSN / _citation.page_first / _citation.page_last / _citation.pdbx_database_id_DOI / _citation.pdbx_database_id_PubMed / _citation.title / _citation.year / _em_admin.last_update

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Structure visualization

Structure viewerMolecule:
MolmilJmol/JSmol

Downloads & links

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Assembly

Deposited unit
C: Hemagglutinin
D: KL-BHA-3D7 heavy chain
E: KL-BHA-3D7 light chain
H: KL-BHA-3D7 heavy chain
L: KL-BHA-3D7 light chain
A: Hemagglutinin
B: Hemagglutinin
hetero molecules


Theoretical massNumber of molelcules
Total (without water)224,54915
Polymers221,0747
Non-polymers3,4758
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

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Protein , 1 types, 3 molecules CAB

#1: Protein Hemagglutinin


Mass: 56616.316 Da / Num. of mol.: 3
Source method: isolated from a genetically manipulated source
Source: (gene. exp.) Influenza B virus (B/Beijing/13-21/2013)
Strain: B/Beijing/13-21/2013 / Gene: HA / Production host: Spodoptera frugiperda (fall armyworm) / References: UniProt: A0A4P8YRB6

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Antibody , 2 types, 4 molecules DHEL

#2: Antibody KL-BHA-3D7 heavy chain


Mass: 13419.956 Da / Num. of mol.: 2
Source method: isolated from a genetically manipulated source
Source: (gene. exp.) Mus musculus (house mouse) / Production host: Mus musculus (house mouse)
#3: Antibody KL-BHA-3D7 light chain


Mass: 12192.493 Da / Num. of mol.: 2
Source method: isolated from a genetically manipulated source
Source: (gene. exp.) Mus musculus (house mouse) / Production host: Mus musculus (house mouse)

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Sugars , 3 types, 8 molecules

#4: Polysaccharide 2-acetamido-2-deoxy-beta-D-glucopyranose-(1-4)-2-acetamido-2-deoxy-beta-D-glucopyranose


Type: oligosaccharide / Mass: 424.401 Da / Num. of mol.: 3
Source method: isolated from a genetically manipulated source
DescriptorTypeProgram
DGlcpNAcb1-4DGlcpNAcb1-ROHGlycam Condensed SequenceGMML 1.0
WURCS=2.0/1,2,1/[a2122h-1b_1-5_2*NCC/3=O]/1-1/a4-b1WURCSPDB2Glycan 1.1.0
[][D-1-deoxy-GlcpNAc]{[(4+1)][b-D-GlcpNAc]{}}LINUCSPDB-CARE
#5: Polysaccharide beta-D-mannopyranose-(1-4)-2-acetamido-2-deoxy-beta-D-glucopyranose-(1-4)-2-acetamido-2-deoxy-beta- ...beta-D-mannopyranose-(1-4)-2-acetamido-2-deoxy-beta-D-glucopyranose-(1-4)-2-acetamido-2-deoxy-beta-D-glucopyranose


Type: oligosaccharide / Mass: 586.542 Da / Num. of mol.: 3
Source method: isolated from a genetically manipulated source
DescriptorTypeProgram
DManpb1-4DGlcpNAcb1-4DGlcpNAcb1-ROHGlycam Condensed SequenceGMML 1.0
WURCS=2.0/2,3,2/[a2122h-1b_1-5_2*NCC/3=O][a1122h-1b_1-5]/1-1-2/a4-b1_b4-c1WURCSPDB2Glycan 1.1.0
[][D-1-deoxy-GlcpNAc]{[(4+1)][b-D-GlcpNAc]{[(4+1)][b-D-Manp]{}}}LINUCSPDB-CARE
#6: Sugar ChemComp-NAG / 2-acetamido-2-deoxy-beta-D-glucopyranose / N-acetyl-beta-D-glucosamine / 2-acetamido-2-deoxy-beta-D-glucose / 2-acetamido-2-deoxy-D-glucose / 2-acetamido-2-deoxy-glucose / N-ACETYL-D-GLUCOSAMINE


Type: D-saccharide, beta linking / Mass: 221.208 Da / Num. of mol.: 2 / Source method: obtained synthetically / Formula: C8H15NO6
IdentifierTypeProgram
DGlcpNAcbCONDENSED IUPAC CARBOHYDRATE SYMBOLGMML 1.0
N-acetyl-b-D-glucopyranosamineCOMMON NAMEGMML 1.0
b-D-GlcpNAcIUPAC CARBOHYDRATE SYMBOLPDB-CARE 1.0
GlcNAcSNFG CARBOHYDRATE SYMBOLGMML 1.0

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Details

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: Cryo-EM structure of B/Phuket/3073/2013 hemagglutinin trimer in complex with two KL-BHA-3D7 Fab fragments
Type: COMPLEX
Details: B/Phuket/3073/2013 hemagglutinin expressed using Sf9 insect cells
Entity ID: #1-#3 / Source: RECOMBINANT
Source (natural)Organism: Mus musculus (house mouse)
Source (recombinant)Organism: Mus musculus (house mouse)
Buffer solutionpH: 7.5
SpecimenEmbedding applied: NO / Shadowing applied: NO / Staining applied: NO / Vitrification applied: YES
VitrificationInstrument: FEI VITROBOT MARK IV / Cryogen 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: SPOT SCAN
Electron lensMode: BRIGHT FIELD / Nominal defocus max: 2500 nm / Nominal defocus min: 1500 nm
Image recordingElectron dose: 58.69 e/Å2 / Film or detector model: GATAN K3 BIOQUANTUM (6k x 4k)

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Processing

EM software
IDNameVersionCategory
1Topaz0.2.5aparticle selection
2PHENIX1.21.2_5419model refinement
13cryoSPARC3D reconstruction
CTF correctionType: PHASE FLIPPING AND AMPLITUDE CORRECTION
SymmetryPoint symmetry: C1 (asymmetric)
3D reconstructionResolution: 3.98 Å / Resolution method: FSC 0.143 CUT-OFF / Num. of particles: 118085 / Symmetry type: POINT
RefinementCross valid method: NONE

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