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Screening for the Location of RNA Using the Chloride Ion Distribution in Simulations of Virus Capsids
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Computational and Systems Biology. Uppsala University, Science for Life Laboratory, SciLifeLab.
Uppsala University, Disciplinary Domain of Science and Technology, Biology, Department of Cell and Molecular Biology, Computational and Systems Biology. Uppsala University, Science for Life Laboratory, SciLifeLab.
2012 (English)In: Journal of Chemical Theory and Computation, ISSN 1549-9618, E-ISSN 1549-9626, Vol. 8, no 7, 2474-2483 p.Article in journal (Refereed) Published
Abstract [en]

The complete structure of the genomic material inside a virus capsid remains elusive, although a limited amount of symmetric nucleic acid can be resolved in the crystal structure of 17 icosahedral viruses. The negatively charged sugar-phosphate backbone of RNA and DNA as well as the large positive charge of the interior surface of the virus capsids suggest that electrostatic complementarity is an important factor in the packaging of the genomes in these viruses. To test how much packing information is encoded by the electrostatic and steric envelope of the capsid interior, we performed extensive all-atom molecular dynamics (MD) simulations of virus capsids with explicit water molecules and solvent ions. The model systems were two small plant viruses in which significant amounts of RNA has been observed by X-ray crystallography: satellite tobacco mosaic virus (STMV, 62% RNA visible) and satellite tobacco necrosis virus (STNV, 34% RNA visible). Simulations of half-capsids of these viruses with no RNA present revealed that the binding sites of RNA correlated well with regions populated by chloride ions, suggesting that it is possible to screen for the binding sites of nucleic acids by determining the equilibrium distribution of negative ions. By including the crystallographically resolved RNA in addition to ions, we predicted the localization of the unresolved RNA in the viruses. Both viruses showed a hot-spot for RNA binding at the S-fold symmetry axis. The MD simulations were compared to predictions of the chloride density based on nonlinear Poisson-Boltzmann equation (PBE) calculations with mobile ions. Although the predictions are superficially similar, the PBE calculations overestimate the ion concentration close to the capsid surface and underestimate it far away, mainly because protein dynamics is not taken into account. Density maps from chloride screening can be used to aid in building atomic models of packaged virus genomes. Knowledge of the principles of genome packaging might be exploited for both antiviral therapy and technological applications.

Place, publisher, year, edition, pages
2012. Vol. 8, no 7, 2474-2483 p.
National Category
Structural Biology Biophysics
URN: urn:nbn:se:uu:diva-172285DOI: 10.1021/ct3002128ISI: 000306245900032OAI: oai:DiVA.org:uu-172285DiVA: diva2:513885
Available from: 2012-04-03 Created: 2012-04-03 Last updated: 2012-08-06Bibliographically approved
In thesis
1. Exploring the Molecular Dynamics of Proteins and Viruses
Open this publication in new window or tab >>Exploring the Molecular Dynamics of Proteins and Viruses
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Knowledge about structure and dynamics of the important biological macromolecules — proteins, nucleic acids, lipids and sugars — helps to understand their function. Atomic-resolution structures of macromolecules are routinely captured with X-ray crystallography and other techniques. In this thesis, simulations are used to explore the dynamics of the molecules beyond the static structures.

Viruses are machines constructed from macromolecules. Crystal structures of them reveal little to no information about their genomes. In simulations of empty capsids, we observed a correlation between the spatial distribution of chloride ions in the solution and the position of RNA in crystals of satellite tobacco necrosis virus (STNV) and satellite tobacco mosaic virus (STMV). In this manner, structural features of the non-symmetric RNA could also be inferred.

The capsid of STNV binds calcium ions on the icosahedral symmetry axes. The release of these ions controls the activation of the virus particle upon infection. Our simulations reproduced the swelling of the capsid upon removal of the ions and we quantified the water permeability of the capsid. The structure and dynamics of the expanded capsid suggest that the disassembly is initiated at the 3-fold symmetry axis.

Several experimental methods require biomolecular samples to be injected into vacuum, such as mass-spectrometry and diffractive imaging of single particles. It is therefore important to understand how proteins and molecule-complexes respond to being aerosolized. In simulations we mimicked the dehydration process upon going from solution into the gas phase. We find that two important factors for structural stability of proteins are the temperature and the level of residual hydration. The simulations support experimental claims that membrane proteins can be protected by a lipid micelle and that a non-membrane protein could be stabilized in a reverse micelle in the gas phase. A water-layer around virus particles would impede the signal in diffractive experiments, but our calculations estimate that it should be possible to determine the orientation of the particle in individual images, which is a prerequisite for three-dimensional reconstruction.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2012. 45 p.
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 919
molecular dynamics, virus dynamics, capsid dissolution, satellite tobacco necrosis virus, satellite tobacco mosaic virus, virus genome structure, gas phase protein structure, water layer, micelle embedded protein, membrane protein
National Category
Biological Sciences Biochemistry and Molecular Biology Biophysics Structural Biology
Research subject
Chemistry with specialization in Biophysics
urn:nbn:se:uu:diva-172284 (URN)978-91-554-8335-7 (ISBN)
Public defence
2012-05-25, B41, Uppsala Biomedicinska Centrum, Husargatan 3, Uppsala, 09:15 (English)
BMC B41, 25/5, 9:15Available from: 2012-05-04 Created: 2012-04-03 Last updated: 2012-08-01Bibliographically approved

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Larsson, Danielvan der Spoel, David
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