Journal: J Mol Biol / Year: 1997 Title: Six molecules of SV40 large T antigen assemble in a propeller-shaped particle around a channel. Authors: M C San Martín / C Gruss / J M Carazo / Abstract: The large T antigen of simian virus 40 (SV40) is a multifunctional regulatory protein, responsible for both the control of viral infection and the required alterations of cellular processes. T ...The large T antigen of simian virus 40 (SV40) is a multifunctional regulatory protein, responsible for both the control of viral infection and the required alterations of cellular processes. T antigen is the only viral protein required for viral DNA replication. It binds specifically to the viral origin and as a helicase unwinds the SV40 DNA bidirectionally. The functional complex is a double hexameric oligomer. In the absence of DNA, but in the presence of ATP or a non-hydrolyzable analog, T antigen assembles into hexamers, which are active as a helicase when a partially single-stranded (3') entry site exists on the substrate. We have used negative staining electron microscopy, single particle image processing and three-dimensional reconstruction with a new algebraic reconstruction techniques (ART) algorithm to study the structure of these hexameric particles in the presence of different nucleotide cofactors (ATP, ADP, and the non-hydrolyzable analogs ATPgammaS and AMP-PNP). In every case a strong 6-fold structure was found, with the six density maxima arranged in a ring-like particle around a channel, and a well-defined vorticity. Because these structural features have recently been found in other prokaryotic helicases, they seem to be strongly related to the activity of the protein, which suggests a general functional model conserved through evolution.
History
Deposition
Feb 12, 2003
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Header (metadata) release
Feb 12, 2003
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Map release
Feb 12, 2003
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Update
May 26, 2011
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Current status
May 26, 2011
Processing site: PDBe / Status: Released
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Structure visualization
Movie
Surface view with section colored by density value
Name: SV40 T antigen / type: sample / ID: 1000 / Oligomeric state: homohexamer / Number unique components: 1
Molecular weight
Theoretical: 500 KDa
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Macromolecule #1: Large T antigen
Macromolecule
Name: Large T antigen / type: protein_or_peptide / ID: 1 / Name.synonym: T antigen / Number of copies: 6 / Oligomeric state: homohexamer / Recombinant expression: Yes
Source (natural)
Organism: Simian virus 40 / synonym: SV40
Molecular weight
Theoretical: 500 KDa
Recombinant expression
Organism: AcNPV
Sequence
GO: DNA replication origin binding / InterPro: T antigen, Ori-binding
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Experimental details
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Structure determination
Method
negative staining
Processing
single particle reconstruction
Aggregation state
particle
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Sample preparation
Concentration
.06 mg/mL
Buffer
pH: 7.5 Details: 20 mM Tris.HCl pH 7.5 5 mM KCl 1.5 mM MgCl2 0.1 mM DTT 4 mM ADP
Staining
Type: NEGATIVE / Details: 2% Uranyl Acetate
Vitrification
Cryogen name: NONE
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Electron microscopy
Microscope
JEOL 1200EXII
Image recording
Category: FILM / Film or detector model: KODAK SO-163 FILM / Digitization - Scanner: EIKONIX IEEE 488 / Number real images: 8 / Average electron dose: 10 e/Å2 / Bits/pixel: 8
Electron beam
Acceleration voltage: 120 kV / Electron source: TUNGSTEN HAIRPIN
Electron optics
Illumination mode: FLOOD BEAM / Imaging mode: BRIGHT FIELD / Cs: 5.6 mm / Nominal magnification: 60000
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