114 research outputs found

    DNA duplex cage structures with icosahedral symmetry

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    A construction method for duplex cage structures with icosahedral symmetry made out of single-stranded DNA molecules is presented and applied to an icosidodecahedral cage. It is shown via a mixture of analytic and computer techniques that there exist realisations of this graph in terms of two circular DNA molecules. These blueprints for the organisation of a cage structure with a noncrystallographic symmetry may assist in the design of containers made from DNA for applications in nanotechnology

    Modeling and simulations of single stranded rna viruses

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    The presented work is the application of recent methodologies on modeling and simulation of single stranded RNA viruses. We first present the methods of modeling RNA molecules using the coarse-grained modeling package, YUP. Coarse-grained models simplify complex structures such as viruses and let us study general behavior of the complex biological systems that otherwise cannot be studied with all-atom details. Second, we modeled the first all-atom T=3, icosahedral, single stranded RNA virus, Pariacoto virus (PaV). The x-ray structure of PaV shows only 35% of the total RNA genome and 88% of the capsid. We modeled both missing portions of RNA and protein. The final model of the PaV demonstrated that the positively charged protein N- terminus was located deep inside the RNA. We propose that the positively charged N- terminal tails make contact with the RNA genome and neutralize the negative charges in RNA and subsequently collapse the RNA/protein complex into an icosahedral virus. Third, we simulated T=1 empty capsids using a coarse-grained model of three capsid proteins as a wedge-shaped triangular capsid unit. We varied the edge angle and the potentials of the capsid units to perform empty capsid assembly simulations. The final model and the potential are further improved for the whole virus assembly simulations. Finally, we performed stability and assembly simulations of the whole virus using coarse-grained models. We tested various strengths of RNA-protein tail and capsid protein-capsid protein attractions in our stability simulations and narrowed our search for optimal potentials for assembly. The assembly simulations were carried out with two different protocols: co-transcriptional and post-transcriptional. The co-transcriptional assembly protocol mimics the assembly occurring during the replication of the new RNA. Proteins bind the partly transcribed RNA in this protocol. The post-transcriptional assembly protocol assumes that the RNA is completely transcribed in the absence of proteins. Proteins later bind to the fully transcribed RNA. We found that both protocols can assemble viruses, when the RNA structure is compact enough to yield a successful virus particle. The post-transcriptional protocol depends more on the compactness of the RNA structure compared to the co-transcriptional assembly protocol. Viruses can exploit both assembly protocols based on the location of RNA replication and the compactness of the final structure of the RNA.PhDCommittee Chair: Stephen C. Harvey; Committee Member: Adegboyega Oyelere; Committee Member: Loren Williams; Committee Member: Rigoberto Hernandez; Committee Member: Roger Wartel

    Structural and Electrostatic Characterization of Pariacoto Virus: Implications for Viral Asembly

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    This is the peer reviewed version of the following article:Devkota, B., Petrov, A., Lemieux, S., Boz, M. B., Tang, L., Schneemann, A., … Harvey, S. C. (2009). Structural and Electrostatic Characterization of Pariacoto Virus: Implications for Viral Asembly. Biopolymers, 91(7), 530–538. http://doi.org/10.1002/bip.21168, which has been published in final form at doi.org/10.1002/bip.21168. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-ArchivingWe present the first all-atom model for the structure of a T=3 virus, pariacoto virus (PaV), which is a non-enveloped, icosahedral RNA virus and a member of the Nodaviridae family. The model is an extension of the crystal structure, which reveals about 88% of the protein structure but only about 35% of the RNA structure. Evaluation of alternative models confirms our earlier observation that the polycationic protein tails must penetrate deeply into the core of the virus, where they stabilize the structure by neutralizing a substantial fraction of the RNA charge. This leads us to propose a model for the assembly of small icosahedral RNA viruses: nonspecific binding of the protein tails to the RNA leads to a collapse of the complex, in a fashion reminiscent of DNA condensation. The globular protein domains are excluded from the condensed phase but are tethered to it, so they accumulate in a shell around the condensed phase, where their concentration is high enough to trigger oligomerization and formation of the mature virus

    Structure of the Macrobrachium rosenbergii nodavirus: a new genus within the Nodaviridae?

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    Macrobrachium rosenbergii nodavirus (MrNV) is a pathogen of freshwater prawns that poses a threat to food security and causes significant economic losses in the aquaculture industries of many developing nations. A detailed understanding of the MrNV virion structure will inform the development of strategies to control outbreaks. The MrNV capsid has also been engineered to display heterologous antigens, and thus knowledge of its atomic resolution structure will benefit efforts to develop tools based on this platform. Here, we present an atomic-resolution model of the MrNV capsid protein (CP), calculated by cryogenic electron microscopy (cryoEM) of MrNV virus-like particles (VLPs) produced in insect cells, and three-dimensional (3D) image reconstruction at 3.3 Å resolution. CryoEM of MrNV virions purified from infected freshwater prawn post-larvae yielded a 6.6 Å resolution structure, confirming the biological relevance of the VLP structure. Our data revealed that unlike other known nodavirus structures, which have been shown to assemble capsids having trimeric spikes, MrNV assembles a T = 3 capsid with dimeric spikes. We also found a number of surprising similarities between the MrNV capsid structure and that of the Tombusviridae: 1) an extensive network of N-terminal arms (NTAs) lines the capsid interior, forming long-range interactions to lace together asymmetric units; 2) the capsid shell is stabilised by 3 pairs of Ca2+ ions in each asymmetric unit; 3) the protruding spike domain exhibits a very similar fold to that seen in the spikes of the tombusviruses. These structural similarities raise questions concerning the taxonomic classification of MrNV

    The T=1 capsid protein of Penicillium chrysogenum virus is formed by a repeated helix-rich core indicative of gene duplication

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    et al.Penicillium chrysogenum virus (PcV), a member of the Chrysoviridae family, is a double-stranded RNA (dsRNA) fungal virus with a multipartite genome, with each RNA molecule encapsidated in a separate particle. Chrysoviruses lack an extracellular route and are transmitted during sporogenesis and cell fusion. The PcV capsid, based on a T=1 lattice containing 60 subunits of the 982-amino-acid capsid protein, remains structurally undisturbed throughout the viral cycle, participates in genome metabolism, and isolates the virus genome from host defense mechanisms. Using three-dimensional cryoelectron microscopy, we determined the structure of the PcV virion at 8.0 Å resolution. The capsid protein has a high content of rod-like densities characteristic of α-helices, forming a repeated α-helical core indicative of gene duplication. Whereas the PcV capsid protein has two motifs with the same fold, most dsRNA virus capsid subunits consist of dimers of a single protein with similar folds. The spatial arrangement of the α-helical core resembles that found in the capsid protein of the L-A virus, a fungal totivirus with an undivided genome, suggesting a conserved basic fold. The encapsidated genome is organized in concentric shells; whereas the inner dsRNA shells are well defined, the outermost layer is dense due to numerous interactions with the inner capsid surface, specifically, six interacting areas per monomer. The outermost genome layer is arranged in an icosahedral cage, sufficiently well ordered to allow for modeling of an A-form dsRNA. The genome ordering might constitute a framework for dsRNA transcription at the capsid interior and/or have a structural role for capsid stability. Copyright © 2010, American Society for Microbiology. All Rights Reserved.This work was supported by grants from the Spanish Ministry of Science and Innovation (BFU 2008-02328/BMC and S-0505-Mat-0238 to J.L.C. and BIO2008-02361 to J.R.C.) and the NIH Intramural Research Program with support from the Center for Information Technology.Peer Reviewe

    Asymmetric Genome Organization in an RNA Virus Revealed via Graph-Theoretical Analysis of Tomographic Data

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    Cryo-electron microscopy permits 3-D structures of viral pathogens to be determined in remarkable detail. In particular, the protein containers encapsulating viral genomes have been determined to high resolution using symmetry averaging techniques that exploit the icosahedral architecture seen in many viruses. By contrast, structure determination of asymmetric components remains a challenge, and novel analysis methods are required to reveal such features and characterize their functional roles during infection. Motivated by the important, cooperative roles of viral genomes in the assembly of single-stranded RNA viruses, we have developed a new analysis method that reveals the asymmetric structural organization of viral genomes in proximity to the capsid in such viruses. The method uses geometric constraints on genome organization, formulated based on knowledge of icosahedrally-averaged reconstructions and the roles of the RNA-capsid protein contacts, to analyse cryo-electron tomographic data. We apply this method to the low-resolution tomographic data of a model virus and infer the unique asymmetric organization of its genome in contact with the protein shell of the capsid. This opens unprecedented opportunities to analyse viral genomes, revealing conserved structural features and mechanisms that can be targeted in antiviral drug desig

    Elucidating the structural mechanisms of capsid stability and assembly using a hyperthermophilic bacteriophage

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    Nearly all viruses encapsulate their genomes in protective protein shells known as capsids. Capsids self-assemble from repeating protein subunits, which surround the viral genome. Many viruses use a powerful biomotor to pump DNA into preformed capsid shells. Therefore, not only does the capsid protect the genome from environmental stress, it additionally stabilizes against high internal pressure caused by the tightly-packaged genome inside. To understand how capsids remain stable despite extreme conditions, I use thermophilic bacteriophage P74-26 as a model to probe the structural mechanisms that govern capsid assembly and stability. P74-26 capsids have a similar architecture to capsids of mesophilic tailed bacteriophages, allowing direct comparison to elucidate the structural basis of enhanced thermostability. Here I determine the structure of the P74-26 capsid decoration protein, which contains a core beta-barrel domain termed the ‘beta-tulip’ domain. The beta-tulip domain is conserved in structural proteins from both Herpesviruses and phage, as well as a broad-spectrum Cas9 inhibitor, providing evidence of shared evolutionary ancestry. Additionally, my high-resolution structure of the P74-26 virion capsid reveals unique interdigitated architectural features that contribute to enhanced stability in the thermophile. P74-26 has a significantly larger capsid than related mesophiles yet retains the same icosahedral geometry, demonstrating a novel mechanism for increasing capsid capacity. Furthermore, my thesis work explores capsid assembly and maturation mechanisms in vitro, establishing P74-26 as a platform for future development of novel nanoparticles and therapeutic delivery systems. Taken together, this work illuminates the incredible stability of a thermophilic virus and illustrates its utility as a powerful tool for studying viral maturation
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