The capillarity of nanometric water menisci confined inside closed-geometry viral cages

Abstract

We present an investigation of water menisci confined in closed geometries by studying the structural effects of their capillary forces on viruses during the final stage of desiccation. We used individual particles of the bacteriophage 29 and the minute virus of mice. In both cases the genomic DNA was ejected from the capsid. However, although the structural integrity of the minute virus of mice was essentially preserved, the 29 capsid underwent a wall-to-wall collapse. We provide evidence that the capillary forces of water confined inside the viruses are mainly responsible for these effects. Moreover, by performing theoretical simulations with a lattice gas model, we found that some structural differences between these 2 viruses may be crucial to explain the different ways in which they are affected by water menisci forces confined at the nanoscale.atomic force microscopy ͉ capillary forces ͉ water ͉ DNA ejection ͉ virus T he action of capillary forces created by water menisci is very important in wetting-dewetting processes taking place at the liquid-gas interface (1). Moreover, water menisci at the nanoscale play a central role in many phenomena, such us hydration forces in biology and colloid science (2, 3). A lot of effort has been dedicated to the understanding of the shape of, and forces exerted by, water menisci in a variety of geometries. All of the systems studied so far consist of nonclosed geometries where water is confined between 2 surfaces, such us surfacenanosphere systems (4-6) and micro and nanochannels (7, 8); or systems with openings as big as the cavity itself, such us carbon nanotubes (9, 10). Thus far, no attention has been paid to the influence of the water meniscus on the containing structure or to out-of-equilibrium systems. Herein, we present experiments on a closed-geometry container, such as a virus particle, subjected to the capillary action of water menisci confined up to the final stages of a desiccation process. By investigating the initial and final stages of these biological cavities, we deduce the capillarity of the confined water by using numerical simulations.We have chosen 2 geometrically different icosahedral viral models, Bacillus subtilis bacteriophage 29 and the minute virus of mice (MVM). The capsid of phage 29 (54 ϫ 42 nm in size, Fig. 1A) is assembled from 6 different structural polypeptides and encapsidates a double-stranded (ds) DNA molecule (11,12). In one of the end caps, the central pentamer is replaced by the connector complex. In the complete virion, a proteinaceous tail complex is attached to the connector. The MVM encloses a single-stranded (ss) DNA molecule and is one of the smallest and structurally simplest (T ϭ 1) viruses known (25 nm in diameter, Fig. 1B) (13). We have used atomic force microscopy (AFM) (14) to investigate the structural effects of desiccation on DNA-filled virions and empty capsids (devoid of DNA), for both 29 and MVM. Desiccation produced the ejection of DNA from both 29 and MVM virions and led to a full collapse of the 29 capsid, whe...

Direct measurement of the dielectric polarization properties of DNA

“…S4B). We assumed the core to be fully occupied by DNA because upon desiccation the internal phage proteins were presumably ejected together with a fraction of condensed DNA (24,35). If, on the other hand, a small amount of internal phage proteins had remained inside, the fact that they have been found to give the same dielectric response as the shell proteins and occupy a small fraction of the whole viral volume would make our model a reasonable approximation.…”

“…S1 and S2), and then with 4 M guanidinium chloride (GuHCl) to force their collapse, thus avoiding the formation of a water meniscus inside (35). In transmission electron microscopy (TEM) images (Fig.…”

Mutations at the Base of the Icosahedral Five-Fold Cylinders of Minute Virus of Mice Induce 3′-to-5′ Genome Uncoating and Critically Impair Entry Functions

“…However, this genome can also be ejected from the otherwise intact infectious virion at physiological temperatures, again in a 3=-to-5= direction, by divalent cation depletion, in a process that leaves the 5= end of the genome firmly complexed with the particle (7). Similarly, it has been shown that during the final stages of desiccation, MVM ejects its genome from the capsid, which nevertheless remains intact, resisting collapse or disintegration (4). These observations raise the possibility that the exceptionally robust MVM particle may have specifically evolved to expose the 3= end of its genome in vivo in response to a physiological stimulus, undergoing a conformational shift that leaves the uncoated DNA associated with the intact capsid, which might then play additional roles in the viral life cycle.…”

Microscopie à force atomique pour l’étude du cycle viral

“…À ce jour, outre les études concernant le VIH-1, des études d'imagerie par AFM ont été réalisées sur plusieurs types de virus comme les bactériophages [27], des parvovirus [28], ou des virus plus complexes, comme le HSV (virus de l'herpès simplex) [29]. Comme en cryo-EM, la résolution de cette méthode est telle qu'il est possible d'observer les protubérances des protéines de structure de certains virus non enveloppés qui sont en général à symétrie icosaédrique, et d'en déterminer leur nombre de triangulation ainsi que leurs axes de symétrie [30].…”