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- EMDB-75658: Subtomogram Average of the Ribosome-Multipass Translocon-EMC Complex -

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Basic information

Entry
Database: EMDB / ID: EMD-75658
TitleSubtomogram Average of the Ribosome-Multipass Translocon-EMC Complex
Map data
Sample
  • Organelle or cellular component: ER-membrane associated ribosomes
KeywordsComplex / Translation / ER / MEMBRANE PROTEIN
Biological speciesHomo sapiens (human)
Methodsubtomogram averaging / cryo EM / Resolution: 21.8 Å
AuthorsRollins MG / Keenan RJ
Funding support United States, 2 items
OrganizationGrant numberCountry
National Institutes of Health/National Institute of General Medical Sciences (NIH/NIGMS)R35GM145374 United States
National Institutes of Health/National Institute of General Medical Sciences (NIH/NIGMS)GM139168 United States
CitationJournal: Nat Struct Mol Biol / Year: 2026
Title: Cotranslational membrane protein biogenesis by an EMC-bound translocon.
Authors: Madeline G Rollins / Josephine Tang / Yu Wan / Arunkumar Sundaram / Haoxi Wu / Qianru Li / Juliette Fedry / Ramanujan S Hegde / Zhe Ji / Robert J Keenan /
Abstract: Secretory and membrane protein biogenesis occurs at ribosome-bound translocons in the endoplasmic reticulum (ER) membrane. Translocons consist of the Sec61 protein-conducting channel and various ...Secretory and membrane protein biogenesis occurs at ribosome-bound translocons in the endoplasmic reticulum (ER) membrane. Translocons consist of the Sec61 protein-conducting channel and various maturation factors including chaperones, modification enzymes and membrane insertases, which assemble dynamically in response to the biogenesis needs of a nascent polypeptide. In human cells, nascent multipass membrane proteins utilize the ER membrane protein complex (EMC) and the multipass translocon (MPT), but how these factors are deployed during biogenesis is unknown. Here we combine selective ribosome profiling, cryo-electron tomography and site-specific photocrosslinking to reveal the substrate range, timing and mechanism of EMC recruitment. We show that multipass proteins initially engage the MPT for insertion and chaperoning, with EMC being recruited when substrates begin to exceed the cytosolic or intramembrane capacity of MPT. Substrate-engaged EMC is observed at the interface between the MPT's protected membrane cavity and the bulk ER membrane, where it is poised for insertion, chaperoning and assembly. These results show how EMC and MPT cooperate at the ribosome-bound translocon to facilitate multipass membrane protein biogenesis.
History
DepositionFeb 19, 2026-
Header (metadata) releaseOct 21, 2026-
Map releaseOct 21, 2026-
UpdateOct 21, 2026-
Current statusOct 21, 2026Processing site: RCSB / Status: Released

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Structure visualization

Supplemental images

emd_75658.png

Downloads & links

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Map

FileDownload / File: emd_75658.map.gz / Format: CCP4 / Size: 299.1 MB / Type: IMAGE STORED AS FLOATING POINT NUMBER (4 BYTES)
Projections & slices

Image control

Size
Brightness
Contrast
Others
AxesZ (Sec.)Y (Row.)X (Col.)
2.1 Å/pix.
x 428 pix.
= 898.8 Å		2.1 Å/pix.
x 428 pix.
= 898.8 Å		2.1 Å/pix.
x 428 pix.
= 898.8 Å

Surface

Projections

Slices (1/3)

Slices (1/2)

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Images are generated by Spider.

Voxel sizeX=Y=Z: 2.1 Å
Density

Histogram

Histogram (log scale)
Contour LevelBy AUTHOR: 0.0035
Minimum - Maximum-0.002821923 - 0.017599981
Average (Standard dev.)0.0002311154 (±0.0011085982)
SymmetrySpace group: 1
Details

EMDB XML:

Map geometry
Axis orderXYZ
Origin000
Dimensions428428428
Spacing428428428
CellA=B=C: 898.8 Å
α=β=γ: 90.0 °

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Supplemental data

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Additional map: #1

Fileemd_75658_additional_1.map
Projections & Slices
AxesZYX

Projections

Slices (1/2)
Density Histograms

Histogram

Histogram (log scale)

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Half map: The half maps have low signal-to-noise ratio (SNR)...

Fileemd_75658_half_map_1.map
AnnotationThe half maps have low signal-to-noise ratio (SNR) and should be Gaussian filtered in Chimera (sDev=4) to visualize densities. The suggested contour level (0.0035) is for the Gaussian-filtered map.
Projections & Slices
AxesZYX

Projections

Slices (1/2)
Density Histograms

Histogram

Histogram (log scale)

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Half map: The half maps have low signal-to-noise ratio (SNR)...

Fileemd_75658_half_map_2.map
AnnotationThe half maps have low signal-to-noise ratio (SNR) and should be Gaussian filtered in Chimera (sDev=4) to visualize densities. The suggested contour level (0.0035) is for the Gaussian-filtered map.
Projections & Slices
AxesZYX

Projections

Slices (1/2)
Density Histograms

Histogram

Histogram (log scale)

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Sample components

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Entire : ER-membrane associated ribosomes

EntireName: ER-membrane associated ribosomes
Components
  • Organelle or cellular component: ER-membrane associated ribosomes

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Supramolecule #1: ER-membrane associated ribosomes

SupramoleculeName: ER-membrane associated ribosomes / type: organelle_or_cellular_component / ID: 1 / Parent: 0
Source (natural)Organism: Homo sapiens (human)

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Experimental details

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Structure determination

Methodcryo EM
Processingsubtomogram averaging
Aggregation stateparticle

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Sample preparation

Concentration0.15 mg/mL
BufferpH: 7.5
VitrificationCryogen name: ETHANE / Instrument: LEICA EM GP

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Electron microscopy

MicroscopeTFS KRIOS
Image recordingFilm or detector model: TFS FALCON 4i (4k x 4k) / Average electron dose: 2.45 e/Å2
Electron beamAcceleration voltage: 300 kV / Electron source: FIELD EMISSION GUN
Electron opticsIllumination mode: FLOOD BEAM / Imaging mode: BRIGHT FIELD / Nominal defocus max: 4.0 µm / Nominal defocus min: 2.0 µm
Experimental equipment
Model: Titan Krios / Image courtesy: FEI Company

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Image processing

Final reconstructionApplied symmetry - Point group: C1 (asymmetric) / Resolution.type: BY AUTHOR / Resolution: 21.8 Å / Resolution method: FSC 0.143 CUT-OFF / Software - Name: M (ver. 2.0.0) / Number subtomograms used: 640
ExtractionNumber tomograms: 497 / Number images used: 45320 / Software - Name: PyTom (ver. 0.11.0) / Software - details: used pytom-match-pick
CTF correctionSoftware - Name: Warp (ver. 2.0.0) / Type: PHASE FLIPPING AND AMPLITUDE CORRECTION
Final 3D classificationSoftware - Name: RELION (ver. 5.0.1)
Final angle assignmentType: MAXIMUM LIKELIHOOD / Software - Name: M (ver. 2.0.0)
FSC plot (resolution estimation)

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