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Nonequilibrium self-assembly dynamics of icosahedral viral capsids packaging genome or polyelectrolyte.

ABSTRACT: The survival of viruses partly relies on their ability to self-assemble inside host cells. Although coarse-grained simulations have identified different pathways leading to assembled virions from their components, experimental evidence is severely lacking. Here, we use time-resolved small-angle X-ray scattering to uncover the nonequilibrium self-assembly dynamics of icosahedral viral capsids packaging their full RNA genome. We reveal the formation of amorphous complexes via an en masse pathway and their relaxation into virions via a synchronous pathway. The binding energy of capsid subunits on the genome is moderate (~7k_BT₀, with k_B the Boltzmann constant and T₀?=?298?K, the room temperature), while the energy barrier separating the complexes and the virions is high (~?20k_BT₀). A synthetic polyelectrolyte can lower this barrier so that filled capsids are formed in conditions where virions cannot build up. We propose a representation of the dynamics on a free energy landscape.

SUBMITTER: Chevreuil M

PROVIDER: S-EPMC6078970 | biostudies-literature | 2018 Aug

REPOSITORIES: biostudies-literature

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Nonequilibrium self-assembly dynamics of icosahedral viral capsids packaging genome or polyelectrolyte.

Chevreuil Maelenn M Law-Hine Didier D Chen Jingzhi J Bressanelli Stéphane S Combet Sophie S Constantin Doru D Degrouard Jéril J Möller Johannes J Zeghal Mehdi M Tresset Guillaume G

Nature communications 20180806 1

The survival of viruses partly relies on their ability to self-assemble inside host cells. Although coarse-grained simulations have identified different pathways leading to assembled virions from their components, experimental evidence is severely lacking. Here, we use time-resolved small-angle X-ray scattering to uncover the nonequilibrium self-assembly dynamics of icosahedral viral capsids packaging their full RNA genome. We reveal the formation of amorphous complexes via an en masse pathway a ...[more]

PMID: 30082710

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Project description:Spherical viruses are remarkably well characterized by the Triangulation (T) number developed by Casper and Klug. The T-number specifies how many viral capsid proteins are required to cover the virus, as well as how they are further subdivided into pentamer and hexamer subunits. The T-number however does not constrain the orientations of these proteins within the subunits or dictate where the proteins should place their protruding features. These protrusions often take the form of loops, spires and helices, and are significant because they aid in stability of the capsid as well as recognition by the host organism. Until now there has be no overall understanding of the placement of protrusions for spherical viruses, other than they have icosahedral symmetry. We constructed a set of gauge points based upon the work affine extensions of Keef and Twarock, which have fixed relative angular locations with which to measure the locations of these features. This work adds a new element to our understanding of the geometric arrangement of spherical viral capsid proteins; chiefly that the locations of protruding features are not found stochastically distributed in an icosahedral manner across the viral surface, but instead these features are found only in specific locations along the 15 icosahedral great circles. We have found that this result holds true as the T number and viral capsids size increases, suggesting an underlying geometric constraint on their locations. This is in spite of the fact that the constraints on the pentamers and hexamer orientations change as a function of T-number, as you need to accommodate more hexamers in the same solid angle between pentamers. The existence of this angular constraint of viral capsids suggests that there is a fitness or energetic benefit to the virus placing its protrusions in this manner. This discovery may have profound impacts on identifying and eliminating viral pathogens, understanding evolutionary constraints as well as bioengineering for capsid drug delivery systems. This result also suggests that in addition to biochemical attachment restrictions, there are additional geometric constraints that should be adhered to when modifying protein capsids.

Dataset Information

Nonequilibrium self-assembly dynamics of icosahedral viral capsids packaging genome or polyelectrolyte.

Publications

Nonequilibrium self-assembly dynamics of icosahedral viral capsids packaging genome or polyelectrolyte.

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