RESUMO
A majority of viruses are composed of long single-stranded genomic RNA molecules encapsulated by protein shells with diameters of just a few tens of nanometers. We examine the extent to which these viral RNAs have evolved to be physically compact molecules to facilitate encapsulation. Measurements of equal-length viral, non-viral, coding and non-coding RNAs show viral RNAs to have among the smallest sizes in solution, i.e., the highest gel-electrophoretic mobilities and the smallest hydrodynamic radii. Using graph-theoretical analyses we demonstrate that their sizes correlate with the compactness of branching patterns in predicted secondary structure ensembles. The density of branching is determined by the number and relative positions of 3-helix junctions, and is highly sensitive to the presence of rare higher-order junctions with 4 or more helices. Compact branching arises from a preponderance of base pairing between nucleotides close to each other in the primary sequence. The density of branching represents a degree of freedom optimized by viral RNA genomes in response to the evolutionary pressure to be packaged reliably. Several families of viruses are analyzed to delineate the effects of capsid geometry, size and charge stabilization on the selective pressure for RNA compactness. Compact branching has important implications for RNA folding and viral assembly.
Assuntos
Conformação de Ácido Nucleico , RNA Viral/química , Pareamento de Bases , Bromovirus/química , Bromovirus/genética , Eletroforese em Gel de Ágar , Genoma Viral , Levivirus/química , Levivirus/genética , Modelos Moleculares , Dobramento de RNA , Vírus de RNA/química , Vírus de RNA/genética , RNA Viral/genética , Espectrometria de Fluorescência , Togaviridae/química , Togaviridae/genética , Montagem de Vírus/genéticaRESUMO
We report the first proof-of-principle demonstration of photoacoustic imaging using a contrast agent composed of a plant virus protein shell, which encapsulates indocyanine green (ICG), the only FDA-approved near infrared chromophore. These nano-constructs can provide higher photoacoustic signals than blood in tissue phantoms, and display superior photostability compared to non-encapsulated ICG. Our preliminary results suggest that the constructs do not elicit an acute immunogenic response in healthy mice.
Assuntos
Acústica , Materiais Biomiméticos/química , Meios de Contraste/química , Verde de Indocianina/química , Nanoestruturas/química , Vírus/química , Imunidade Adaptativa/efeitos dos fármacos , Animais , Materiais Biomiméticos/farmacologia , Linhagem Celular Tumoral , Meios de Contraste/farmacologia , Citocinas/metabolismo , Humanos , Injeções Intravenosas , Camundongos , Microscopia Confocal , TemperaturaRESUMO
We have engineered an optical nanoconstruct composed of genome-depleted brome mosaic virus doped with indocyanine green (ICG), an FDA-approved near-infrared (NIR) chromophore. Constructs are highly monodispersed with standard deviation of ±3.8 nm from a mean diameter of 24.3 nm. They are physically stable and exhibit a high degree of optical stability at physiological temperature (37 °C). Using human bronchial epithelial cells, we demonstrate the effectiveness of the constructs for intracellular optical imaging in vitro, with greater than 90% cell viability after 3 h of incubation. These constructs may serve as a potentially nontoxic and multifunctional nanoplatform for site-specific deep-tissue optical imaging, and therapy of disease.
