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- EMDB-62209: CryoEM structure of LTag bound to SV40 AT half origin DNA -

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Basic information

Entry
Database: EMDB / ID: EMD-62209
TitleCryoEM structure of LTag bound to SV40 AT half origin DNA
Map data
Sample
  • Complex: SV40 LTag bound to SV40 AT half origin DNA
    • Complex: SV40 LTag
      • Protein or peptide: Large T antigen
    • Complex: DNA
      • DNA: DNA
      • DNA: DNA
  • Ligand: PHOSPHOAMINOPHOSPHONIC ACID-ADENYLATE ESTER
  • Ligand: MAGNESIUM ION
KeywordsHelicase / ATPase / AT half origin / AMP-PNP / DNA replication / TRANSLOCASE
Function / homology
Function and homology information


symbiont-mediated suppression of host JAK-STAT cascade via inhibition of JAK1 activity / bidirectional double-stranded viral DNA replication / viral DNA genome replication / DNA 3'-5' helicase / symbiont-mediated perturbation of host cell cycle G1/S transition checkpoint / DNA replication origin binding / helicase activity / single-stranded DNA binding / double-stranded DNA binding / symbiont-mediated perturbation of host ubiquitin-like protein modification ...symbiont-mediated suppression of host JAK-STAT cascade via inhibition of JAK1 activity / bidirectional double-stranded viral DNA replication / viral DNA genome replication / DNA 3'-5' helicase / symbiont-mediated perturbation of host cell cycle G1/S transition checkpoint / DNA replication origin binding / helicase activity / single-stranded DNA binding / double-stranded DNA binding / symbiont-mediated perturbation of host ubiquitin-like protein modification / DNA replication / symbiont-mediated suppression of host innate immune response / symbiont-mediated suppression of host type I interferon-mediated signaling pathway / host cell nucleus / ATP hydrolysis activity / zinc ion binding / ATP binding / identical protein binding
Similarity search - Function
Large T antigen, polyomaviridae / Large T antigen, polyomavirus, C-terminal / Zinc finger, large T-antigen D1-type / Origin of replication binding protein / Polyomavirus large T antigen C-terminus / Large T-antigen (T-ag) origin-binding domain (OBD) profile. / Zinc finger large T-antigen (T-ag) D1-type profile. / T antigen, Ori-binding / Zinc finger, large T-antigen D1 domain superfamily / Helicase, superfamily 3, DNA virus ...Large T antigen, polyomaviridae / Large T antigen, polyomavirus, C-terminal / Zinc finger, large T-antigen D1-type / Origin of replication binding protein / Polyomavirus large T antigen C-terminus / Large T-antigen (T-ag) origin-binding domain (OBD) profile. / Zinc finger large T-antigen (T-ag) D1-type profile. / T antigen, Ori-binding / Zinc finger, large T-antigen D1 domain superfamily / Helicase, superfamily 3, DNA virus / Superfamily 3 helicase of DNA viruses domain profile. / DnaJ molecular chaperone homology domain / dnaJ domain profile. / Chaperone J-domain superfamily / DnaJ domain / P-loop containing nucleoside triphosphate hydrolase
Similarity search - Domain/homology
Biological speciesBetapolyomavirus macacae / synthetic construct (others)
Methodsingle particle reconstruction / cryo EM / Resolution: 3.1 Å
AuthorsDanazumi AU / Shahid T / Tehseen M / Alhudhali L / Clark A / Savva CG / Hamdan SM / De Biasio A
Funding support Saudi Arabia, 1 items
OrganizationGrant numberCountry
Other private Saudi Arabia
CitationJournal: Nature / Year: 2025
Title: Structural dynamics of DNA unwinding by a replicative helicase.
Authors: Taha Shahid / Ammar U Danazumi / Muhammad Tehseen / Lubna Alhudhali / Alice R Clark / Christos G Savva / Samir M Hamdan / Alfredo De Biasio /
Abstract: Hexameric helicases are nucleotide-driven molecular machines that unwind DNA to initiate replication across all domains of life. Despite decades of intensive study, several critical aspects of their ...Hexameric helicases are nucleotide-driven molecular machines that unwind DNA to initiate replication across all domains of life. Despite decades of intensive study, several critical aspects of their function remain unresolved: the site and mechanism of DNA strand separation, the mechanics of unwinding propagation, and the dynamic relationship between nucleotide hydrolysis and DNA movement. Here, using cryo-electron microscopy (cryo-EM), we show that the simian virus 40 large tumour antigen (LTag) helicase assembles in the form of head-to-head hexamers at replication origins, melting DNA at two symmetrically positioned sites to establish bidirectional replication forks. Through continuous heterogeneity analysis, we characterize the conformational landscape of LTag on forked DNA under catalytic conditions, demonstrating coordinated motions that drive DNA translocation and unwinding. We show that the helicase pulls the tracking strand through DNA-binding loops lining the central channel, while directing the non-tracking strand out of the rear, in a cyclic process. ATP hydrolysis functions as an 'entropy switch', removing blocks to translocation rather than directly powering DNA movement. Our structures show the allosteric couplings between nucleotide turnover and subunit motions that enable DNA unwinding while maintaining dedicated exit paths for the separated strands. These findings provide a comprehensive model for replication fork establishment and progression that extends from viral to eukaryotic systems. More broadly, they introduce fundamental principles of the mechanism by which ATP-dependent enzymes achieve efficient mechanical work through entropy-driven allostery.
History
DepositionOct 29, 2024-
Header (metadata) releaseFeb 5, 2025-
Map releaseFeb 5, 2025-
UpdateMay 14, 2025-
Current statusMay 14, 2025Processing site: PDBj / Status: Released

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Structure visualization

Supplemental images

emd_62209.png

Downloads & links

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Map

FileDownload / File: emd_62209.map.gz / Format: CCP4 / Size: 125 MB / Type: IMAGE STORED AS FLOATING POINT NUMBER (4 BYTES)
Projections & slices

Image control

Size
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AxesZ (Sec.)Y (Row.)X (Col.)
0.93 Å/pix.
x 320 pix.
= 297.6 Å		0.93 Å/pix.
x 320 pix.
= 297.6 Å		0.93 Å/pix.
x 320 pix.
= 297.6 Å

Surface

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Images are generated by Spider.

Voxel sizeX=Y=Z: 0.93 Å
Density

Histogram

Histogram (log scale)
Contour LevelBy AUTHOR: 0.262
Minimum - Maximum-0.15789387 - 19.535007
Average (Standard dev.)-0.0056103207 (±0.5625094)
SymmetrySpace group: 1
Details

EMDB XML:

Map geometry
Axis orderXYZ
Origin000
Dimensions320320320
Spacing320320320
CellA=B=C: 297.6 Å
α=β=γ: 90.0 °

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Supplemental data

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Mask #1

Fileemd_62209_msk_1.map
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Additional map: #1

Fileemd_62209_additional_1.map
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Half map: #2

Fileemd_62209_half_map_1.map
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Half map: #1

Fileemd_62209_half_map_2.map
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Sample components

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Entire : SV40 LTag bound to SV40 AT half origin DNA

EntireName: SV40 LTag bound to SV40 AT half origin DNA
Components
  • Complex: SV40 LTag bound to SV40 AT half origin DNA
    • Complex: SV40 LTag
      • Protein or peptide: Large T antigen
    • Complex: DNA
      • DNA: DNA
      • DNA: DNA
  • Ligand: PHOSPHOAMINOPHOSPHONIC ACID-ADENYLATE ESTER
  • Ligand: MAGNESIUM ION

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Supramolecule #1: SV40 LTag bound to SV40 AT half origin DNA

SupramoleculeName: SV40 LTag bound to SV40 AT half origin DNA / type: complex / ID: 1 / Parent: 0 / Macromolecule list: #1-#3

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Supramolecule #2: SV40 LTag

SupramoleculeName: SV40 LTag / type: complex / ID: 2 / Parent: 1 / Macromolecule list: #1
Source (natural)Organism: Betapolyomavirus macacae

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Supramolecule #3: DNA

SupramoleculeName: DNA / type: complex / ID: 3 / Parent: 1 / Macromolecule list: #2-#3
Source (natural)Organism: synthetic construct (others) / Synthetically produced: Yes

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Macromolecule #1: Large T antigen

MacromoleculeName: Large T antigen / type: protein_or_peptide / ID: 1 / Number of copies: 6 / Enantiomer: LEVO / EC number: DNA 3'-5' helicase
Source (natural)Organism: Betapolyomavirus macacae
Molecular weightTheoretical: 41.812664 KDa
Recombinant expressionOrganism: Spodoptera frugiperda (fall armyworm)
SequenceString: KQVSWKLVTE YAMETKCDDV LLLLGMYLEF QYSFEMCLKC IKKEQPSHYK YHEKHYANAA IFADSKNQKT ICQQAVDTVL AKKRVDSLQ LTREQMLTNR FNDLLDRMDI MFGSTGSADI EEWMAGVAWL HCLLPKMDSV VYDFLKCMVY NIPKKRYWLF K GPIDSGKT ...String:
KQVSWKLVTE YAMETKCDDV LLLLGMYLEF QYSFEMCLKC IKKEQPSHYK YHEKHYANAA IFADSKNQKT ICQQAVDTVL AKKRVDSLQ LTREQMLTNR FNDLLDRMDI MFGSTGSADI EEWMAGVAWL HCLLPKMDSV VYDFLKCMVY NIPKKRYWLF K GPIDSGKT TLAAALLELC GGKALNVNLP LDRLNFELGV AIDQFLVVFE DVKGTGGESR DLPSGQGINN LDNLRDYLDG SV KVNLEKK HLNKRTQIFP PGIVTMNEYS VPKTLQARFV KQIDFRPKDY LKHCLERSEF LLEKRIIQSG IALLLMLIWY RPV AEFAQS IQSRIVEWKE RLDKEFSLSV YQKMKFNVAM GIGVLD

UniProtKB: Large T antigen

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Macromolecule #2: DNA

MacromoleculeName: DNA / type: dna / ID: 2 / Number of copies: 1 / Classification: DNA
Source (natural)Organism: synthetic construct (others)
Molecular weightTheoretical: 3.08711 KDa
SequenceString:
(DA)(DA)(DA)(DA)(DA)(DA)(DA)(DA)(DA)(DA)

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Macromolecule #3: DNA

MacromoleculeName: DNA / type: dna / ID: 3 / Number of copies: 1 / Classification: DNA
Source (natural)Organism: synthetic construct (others)
Molecular weightTheoretical: 4.517935 KDa
SequenceString:
(DT)(DT)(DT)(DT)(DT)(DT)(DT)(DT)(DT)(DT) (DT)(DT)(DT)(DT)(DT)

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Macromolecule #4: PHOSPHOAMINOPHOSPHONIC ACID-ADENYLATE ESTER

MacromoleculeName: PHOSPHOAMINOPHOSPHONIC ACID-ADENYLATE ESTER / type: ligand / ID: 4 / Number of copies: 6 / Formula: ANP
Molecular weightTheoretical: 506.196 Da
Chemical component information

ChemComp-ANP:
PHOSPHOAMINOPHOSPHONIC ACID-ADENYLATE ESTER / AMP-PNP, energy-carrying molecule analogue*YM

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Macromolecule #5: MAGNESIUM ION

MacromoleculeName: MAGNESIUM ION / type: ligand / ID: 5 / Number of copies: 6 / Formula: MG
Molecular weightTheoretical: 24.305 Da

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Experimental details

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Structure determination

Methodcryo EM
Processingsingle particle reconstruction
Aggregation stateparticle

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Sample preparation

Concentration0.5 mg/mL
BufferpH: 8
GridModel: Quantifoil R2/2 / Material: GOLD / Mesh: 300 / Pretreatment - Type: GLOW DISCHARGE / Pretreatment - Time: 30 sec.
VitrificationCryogen name: ETHANE / Chamber humidity: 100 % / Chamber temperature: 277.15 K / Instrument: FEI VITROBOT MARK IV

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Electron microscopy

MicroscopeTFS KRIOS
Image recordingFilm or detector model: FEI FALCON IV (4k x 4k) / Average electron dose: 43.0 e/Å2
Electron beamAcceleration voltage: 300 kV / Electron source: FIELD EMISSION GUN
Electron opticsC2 aperture diameter: 50.0 µm / Illumination mode: FLOOD BEAM / Imaging mode: BRIGHT FIELD / Cs: 2.7 mm / Nominal defocus max: 2.6 µm / Nominal defocus min: 1.1 µm / Nominal magnification: 130000
Sample stageSpecimen holder model: FEI TITAN KRIOS AUTOGRID HOLDER / Cooling holder cryogen: NITROGEN
Experimental equipment
Model: Titan Krios / Image courtesy: FEI Company

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Image processing

CTF correctionType: NONE
Startup modelType of model: OTHER / Details: Abinitio
Final reconstructionResolution.type: BY AUTHOR / Resolution: 3.1 Å / Resolution method: FSC 0.143 CUT-OFF / Number images used: 198000
Initial angle assignmentType: ANGULAR RECONSTITUTION
Final angle assignmentType: ANGULAR RECONSTITUTION
FSC plot (resolution estimation)

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Atomic model buiding 1

RefinementProtocol: FLEXIBLE FIT
Output model

PDB-9kak:
CryoEM structure of LTag bound to SV40 AT half origin DNA

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