Weighing Polyelectrolytes Packaged in Viruslike Particles

Abstract

This Letter reports on the remarkable selectivity of capsid proteins for packaging synthetic polyelectrolytes in viruslike particles. By applying the contrast variation method in small-angle neutron scattering, we accurately estimated the mean mass of packaged polyelectrolytes ⟨Mp⟩ and that of the surrounding capsid ⟨Mcap⟩. Remarkably, the mass ratio ⟨Mp⟩/⟨Mcap⟩ was invariant for polyelectrolyte molecular weights spanning more than 2 orders of magnitude. To do so, capsids either packaged several chains simultaneously or selectively retained the shortest chains that could fit the capsid interior. Our data are in qualitative agreement with theoretical predictions based on free energy minimization and emphasize the importance of protein self-energy. These findings may give new insights into the nonspecific origin of genome selectivity for a number of viral systems.

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

“…We performed static measurements by small-angle neutron scattering (SANS) with a mixture of subunits and genome in 68% D 2 O at pD 7.5. In this fraction of heavy water, the contrast between RNA and the solvent vanishes, and solely the scattering intensity arising from the proteins is detected 6 . The subunit-to-genome mass ratio ρ in a native virion is about 3.6, but we performed experiments with ρ around 6, which has been found to be the minimal ratio ensuring the complete packaging of genome 43 .…”

“…The genome is packaged during replication in the host cell 1 through an efficient self-assembly process 2 – 4 . The fact that some viruses are able to self-assemble from purified components and to package materials in vitro has promoted the development of engineered viral capsids enclosing synthetic polymers 5 , 6 , heterologous nucleic acids 7 – 10 , nanoemulsion droplets 11 , gold 12 , 13 , and magnetic 14 nanoparticles to name a few. Therefore, understanding the molecular mechanisms of viral self-assembly can help devise therapeutic strategies for inhibiting viral replication 15 , 16 and design functional biocompatible nanocontainers 17 for drug delivery and medical imaging.…”

“…The cowpea chlorotic mottle virus (CCMV) is an icosahedral, single-stranded (ss)RNA plant virus widely used in physical 6 , 8 , 28 and nanotechnological 9 , 10 , 19 , 40 studies. Its T = 3 capsid is made up of 90 chemically identical protein dimers—hereafter called subunits—enclosing the genome shared between four ssRNA segments.…”

Revealing in real-time a multistep assembly mechanism for SV40 virus-like particles

“…In general, it seems that there is a trade-off between the stiffness of the polymer to be encapsulated and the strength of the protein-protein interactions (35,37,39). CCMV has, for instance, a preference for packaging of polystyrene sulfonate (PSS), which favors a collapsed state over singlestranded RNA, which acts like a many-branched polymer (43). For SV40, it is shown that tertiary structure of PSS or RNA and the size of the substrate affect the assembly (19).…”

The Effect of RNA Secondary Structure on the Self-Assembly of Viral Capsids

“…structure determination. In reviewing several previous works that involved the formation of T ¼ 2-sized particles made from CCMV or BMV CPs, it appears that all of these assemblies have resulted in heterogeneous particles (8,29,30,(32)(33)(34). A mutated CCMV CP lacking most of its cationic N-terminal domain has been shown to produce, in vitro, heterogenous, T ¼ 2-sized particles, in addition to producing T ¼ 1 and T ¼ 3 particles.…”