Journal: Nat Commun / Year: 2025 Title: Visualizing influenza A virus assembly by in situ cryo-electron tomography. Authors: Moritz Wachsmuth-Melm / Sarah Peterl / Aidan O'Riain / Jana Makroczyová / Konstantin Fischer / Tim Krischuns / Sílvia Vale-Costa / Maria João Amorim / Petr Chlanda / Abstract: Influenza A virus (IAV) forms pleomorphic particles that package eight ribonucleoprotein complexes (vRNPs), each carrying a distinct RNA genome segment. vRNPs assemble in the nucleus and undergo ...Influenza A virus (IAV) forms pleomorphic particles that package eight ribonucleoprotein complexes (vRNPs), each carrying a distinct RNA genome segment. vRNPs assemble in the nucleus and undergo selective sorting during Rab11a-mediated trafficking to the plasma membrane. Virion assembly is orchestrated by matrix protein 1 (M1), which forms a layer beneath the viral envelope containing hemagglutinin (HA) and neuraminidase (NA). However, molecular details of vRNP distribution, cytosolic trafficking, and coordination of IAV assembly remains unclear. Using in situ cryo-ET, we reveal that HA-containing membranes provide Rab11a-dependent platforms for membrane-assisted vRNP clustering, reducing inter-vRNP distances. In the absence of HA, vRNPs cluster on NA-containing membranes and virus assembly remains intact, indicating that vRNP clustering and trafficking is membrane-assisted but HA independent. The characteristic 7 + 1 vRNP bundle forms concomitantly with budding and is orchestrated by M1 layer assembly that precedes plasma membrane attachment. We further reveal that intracellular M1 forms multilayered helical assemblies of antiparallel dimers, structurally distinct from the M1 layer in virions. These assemblies are compact in the nucleus but partially dissociate in the cytoplasm, likely serving as a reservoir for budding. Together, our findings uncover membrane-assisted vRNP clustering and molecular details of M1 coordinated influenza virus assembly.
Download / File: emd_54375.map.gz / Format: CCP4 / Size: 203.9 MB / Type: IMAGE STORED AS SIGNED BYTE
Annotation
Tomogram showing a NA membrane in an A549wt cell infected with WSN-delHA at 16 hpi.
Voxel size
X=Y=Z: 10.36 Å
Density
Minimum - Maximum
-128.0 - 127.0
Average (Standard dev.)
77.863910000000004 (±8.175553000000001)
Symmetry
Space group: 1
Details
EMDB XML:
Map geometry
Axis order
X
Y
Z
Origin
-208
208
-72
Dimensions
1440
1024
145
Spacing
1024
1440
145
Cell
A: 10608.64 Å / B: 14918.399 Å / C: 1502.2 Å α=β=γ: 90.0 °
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Supplemental data
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Sample components
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Entire : A549wt cell infected with WSNdeltaHA virus at 16 hpi.
Entire
Name: A549wt cell infected with WSNdeltaHA virus at 16 hpi.
Components
Cell: A549wt cell infected with WSNdeltaHA virus at 16 hpi.
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Supramolecule #1: A549wt cell infected with WSNdeltaHA virus at 16 hpi.
Supramolecule
Name: A549wt cell infected with WSNdeltaHA virus at 16 hpi. / type: cell / ID: 1 / Parent: 0
Source (natural)
Organism: Homo sapiens (human) / Organ: Lung
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Experimental details
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Structure determination
Method
cryo EM
Processing
electron tomography
Aggregation state
cell
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Sample preparation
Buffer
pH: 7.4
Vitrification
Cryogen name: ETHANE
Sectioning
Focused ion beam - Instrument: OTHER / Focused ion beam - Ion: OTHER / Focused ion beam - Voltage: 30 / Focused ion beam - Current: 0.05 / Focused ion beam - Duration: 300 / Focused ion beam - Temperature: 95 K / Focused ion beam - Initial thickness: 1000 / Focused ion beam - Final thickness: 150 Focused ion beam - Details: The value given for _em_focused_ion_beam.instrument is TFS Aquilos 2. This is not in a list of allowed values {'OTHER', 'DB235'} so OTHER is written into the XML file.
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Electron microscopy
Microscope
TFS KRIOS
Image recording
Film or detector model: GATAN K3 BIOQUANTUM (6k x 4k) / Average electron dose: 3.3 e/Å2
Electron beam
Acceleration voltage: 300 kV / Electron source: FIELD EMISSION GUN
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