Journal: Nature / Year: 2012 Title: Structure of the immature retroviral capsid at 8 Å resolution by cryo-electron microscopy. Authors: Tanmay A M Bharat / Norman E Davey / Pavel Ulbrich / James D Riches / Alex de Marco / Michaela Rumlova / Carsten Sachse / Tomas Ruml / John A G Briggs / Abstract: The assembly of retroviruses such as HIV-1 is driven by oligomerization of their major structural protein, Gag. Gag is a multidomain polyprotein including three conserved folded domains: MA (matrix), ...The assembly of retroviruses such as HIV-1 is driven by oligomerization of their major structural protein, Gag. Gag is a multidomain polyprotein including three conserved folded domains: MA (matrix), CA (capsid) and NC (nucleocapsid). Assembly of an infectious virion proceeds in two stages. In the first stage, Gag oligomerization into a hexameric protein lattice leads to the formation of an incomplete, roughly spherical protein shell that buds through the plasma membrane of the infected cell to release an enveloped immature virus particle. In the second stage, cleavage of Gag by the viral protease leads to rearrangement of the particle interior, converting the non-infectious immature virus particle into a mature infectious virion. The immature Gag shell acts as the pivotal intermediate in assembly and is a potential target for anti-retroviral drugs both in inhibiting virus assembly and in disrupting virus maturation. However, detailed structural information on the immature Gag shell has not previously been available. For this reason it is unclear what protein conformations and interfaces mediate the interactions between domains and therefore the assembly of retrovirus particles, and what structural transitions are associated with retrovirus maturation. Here we solve the structure of the immature retroviral Gag shell from Mason-Pfizer monkey virus by combining cryo-electron microscopy and tomography. The 8-Å resolution structure permits the derivation of a pseudo-atomic model of CA in the immature retrovirus, which defines the protein interfaces mediating retrovirus assembly. We show that transition of an immature retrovirus into its mature infectious form involves marked rotations and translations of CA domains, that the roles of the amino-terminal and carboxy-terminal domains of CA in assembling the immature and mature hexameric lattices are exchanged, and that the CA interactions that stabilize the immature and mature viruses are almost completely distinct.
History
Deposition
Apr 23, 2012
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Header (metadata) release
May 17, 2012
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Map release
May 25, 2012
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Update
Aug 12, 2015
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Current status
Aug 12, 2015
Processing site: PDBe / Status: Released
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Structure visualization
Movie
Surface view with section colored by density value
Category: FILM / Film or detector model: KODAK SO-163 FILM / Digitization - Scanner: ZEISS SCAI / Digitization - Sampling interval: 7 µm / Number real images: 46 / Average electron dose: 20 e/Å2
Electron beam
Acceleration voltage: 300 kV / Electron source: FIELD EMISSION GUN
Reconstruction carried out using real-space helical reconstruction followed by 3D averaging of the asymmetric unit from assemblies with different helical symmetry parameters.
Final reconstruction
Algorithm: OTHER / Resolution.type: BY AUTHOR / Resolution: 8.0 Å / Resolution method: OTHER / Software - Name: Spider, AV3 / Details: Helical reconstructions were averaged in 3D
CTF correction
Details: Division by 3D CTF^2
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