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- EMDB-75008: Local refinement of both Lmod2s, incoming actin, and the two term... -

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Basic information

Entry
Database: EMDB / ID: EMD-75008
TitleLocal refinement of both Lmod2s, incoming actin, and the two terminal pointed end actins for Two Lmod2s and incoming actin at the pointed end of F-actin
Map data
Sample
  • Complex: Two Lmod2s at the pointed end of F-actin
    • Complex: F-actin
Keywordsactin / Lmod2 / leiomodin / STRUCTURAL PROTEIN
Biological speciesHomo sapiens (human) / Oryctolagus cuniculus (rabbit)
Methodsingle particle reconstruction / cryo EM / Resolution: 3.96 Å
AuthorsBrotzman SB / Palmer NJ / Dominguez R
Funding support United States, 2 items
OrganizationGrant numberCountry
National Institutes of Health/National Institute of General Medical Sciences (NIH/NIGMS)R35 GM161161 United States
National Institutes of Health/National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIH/NIAMS)5T32AR053461-20 United States
CitationJournal: Nat Commun / Year: 2026
Title: Mechanism of actin thin filament pointed-end elongation by leiomodin.
Authors: Shayna B Brotzman / Nicholas J Palmer / Malgorzata Boczkowska / Roberto Dominguez /
Abstract: In non-muscle cells, actin filaments exhibit variable lengths and rapid turnover, with subunits adding primarily at the barbed end. The situation is strikingly different in striated muscle ...In non-muscle cells, actin filaments exhibit variable lengths and rapid turnover, with subunits adding primarily at the barbed end. The situation is strikingly different in striated muscle sarcomeres, where despite rapid turnover, actin thin filaments exhibit uniform length and exchange subunits primarily at the pointed end. This filament length uniformity is tightly regulated by several proteins, including the molecular ruler nebulin in skeletal muscle and the barbed- and pointed-end capping proteins CapZ and tropomodulin (Tmod) in both skeletal and cardiac muscles. Recent studies in cells and animal models have identified leiomodin-2 (Lmod2) as an additional regulator proposed to promote pointed-end elongation to maintain thin filament length. This activity would make leiomodin the only known eukaryotic factor to drive pointed-end elongation, yet its molecular mechanism remains unresolved. Here, we present a series of cryo-electron microscopy structures that support a stepwise elongation mechanism in which two Lmod2 molecules alternate at the pointed end while recruiting actin monomers. These findings establish the molecular basis of pointed-end elongation in muscle sarcomeres and provide a framework for understanding mutations in Lmod2 that cause dilated cardiomyopathy.
History
DepositionJan 7, 2026-
Header (metadata) releaseJun 24, 2026-
Map releaseJun 24, 2026-
UpdateAug 5, 2026-
Current statusAug 5, 2026Processing site: RCSB / Status: Released

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Structure visualization

Supplemental images

emd_75008.png

Downloads & links

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Map

FileDownload / File: emd_75008.map.gz / Format: CCP4 / Size: 471.1 MB / Type: IMAGE STORED AS FLOATING POINT NUMBER (4 BYTES)
Projections & slices

Image control

Size
Brightness
Contrast
Others
AxesZ (Sec.)Y (Row.)X (Col.)
1.07 Å/pix.
x 498 pix.
= 534.852 Å		1.07 Å/pix.
x 498 pix.
= 534.852 Å		1.07 Å/pix.
x 498 pix.
= 534.852 Å

Surface

Projections

Slices (1/3)

Slices (1/2)

Slices (2/3)

Images are generated by Spider.

Voxel sizeX=Y=Z: 1.074 Å
Density

Histogram

Histogram (log scale)
Contour LevelBy AUTHOR: 0.131
Minimum - Maximum-0.30242813 - 0.70258
Average (Standard dev.)-0.0003059802 (±0.01508079)
SymmetrySpace group: 1
Details

EMDB XML:

Map geometry
Axis orderXYZ
Origin000
Dimensions498498498
Spacing498498498
CellA=B=C: 534.852 Å
α=β=γ: 90.0 °

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Supplemental data

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Half map: #1

Fileemd_75008_half_map_1.map
Projections & Slices
AxesZYX

Projections

Slices (1/2)
Density Histograms

Histogram

Histogram (log scale)

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Half map: #2

Fileemd_75008_half_map_2.map
Projections & Slices
AxesZYX

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Histogram

Histogram (log scale)

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Sample components

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Entire : Two Lmod2s at the pointed end of F-actin

EntireName: Two Lmod2s at the pointed end of F-actin
Components
  • Complex: Two Lmod2s at the pointed end of F-actin
    • Complex: F-actin

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Supramolecule #1: Two Lmod2s at the pointed end of F-actin

SupramoleculeName: Two Lmod2s at the pointed end of F-actin / type: complex / ID: 1 / Parent: 0
Source (natural)Organism: Homo sapiens (human)
Molecular weightTheoretical: 1.5 kDa/nm

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Supramolecule #2: F-actin

SupramoleculeName: F-actin / type: complex / ID: 2 / Parent: 1
Source (natural)Organism: Oryctolagus cuniculus (rabbit)

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Experimental details

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Structure determination

Methodcryo EM
Processingsingle particle reconstruction
Aggregation statefilament

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Sample preparation

BufferpH: 7.5
Component:
ConcentrationFormulaName
20.0 mMC8H18N2O4SHEPES
50.0 mMKAcPotassium acetate
1.0 mMC14H24N2O10EGTA
1.0 mMMgCl2magnesium chloride
0.2 mMATPadenosine triphosphate
1.0 mMC4H10O2S2DTT
VitrificationCryogen name: ETHANE / Chamber humidity: 100 % / Chamber temperature: 277 K / Instrument: FEI VITROBOT MARK IV

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Electron microscopy

MicroscopeTFS KRIOS
Image recordingFilm or detector model: GATAN K3 (6k x 4k) / Average electron dose: 49.0 e/Å2
Electron beamAcceleration voltage: 300 kV / Electron source: FIELD EMISSION GUN
Electron opticsIllumination mode: FLOOD BEAM / Imaging mode: BRIGHT FIELD / Nominal defocus max: 2.5 µm / Nominal defocus min: 0.5 µm / Nominal magnification: 81000
Experimental equipment
Model: Titan Krios / Image courtesy: FEI Company

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Image processing

CTF correctionType: NONE
Startup modelType of model: NONE
Final reconstructionResolution.type: BY AUTHOR / Resolution: 3.96 Å / Resolution method: FSC 0.143 CUT-OFF / Software - Name: PHENIX / Number images used: 25835
Initial angle assignmentType: NOT APPLICABLE
Final angle assignmentType: NOT APPLICABLE
FSC plot (resolution estimation)

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Atomic model buiding 1

Initial modelPDB ID:

8f8s


Chain - Source name: PDB / Chain - Initial model type: experimental model

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