In this work, we provide evidence of a mechanism to reinforce the strength of an icosahedral virus by using its genomic DNA as a structural element. The mechanical properties of individual empty capsids and DNA-containing virions of the minute virus of mice are investigated by using atomic force microscopy. The stiffness of the empty capsid is found to be isotropic. Remarkably, the presence of the DNA inside the virion leads to an anisotropic reinforcement of the virus stiffness by Ϸ3%, 40%, and 140% along the fivefold, threefold, and twofold symmetry axes, respectively. A finite element model of the virus indicates that this anisotropic mechanical reinforcement is due to DNA stretches bound to 60 concavities of the capsid. These results, together with evidence of biologically relevant conformational rearrangements of the capsid around pores located at the fivefold symmetry axes, suggest that the bound DNA may reinforce the overall stiffness of the viral particle without canceling the conformational changes needed for its infectivity.capsid ͉ virion ͉ nanomechanics ͉ finite element methods ͉ atomic force microscopy I nvestigation of the mechanical properties of biomolecular assemblies is important to understanding the relationship between physical structure and biological function (1) and for the application of biomaterials in the fabrication of molecular structures (2). Viruses are masterpieces of nanoengineering designed as replicating machines. In most infectious virus particles (virions), the protein shell (capsid) that encloses the nucleic acid genome reveals a minimalist architecture, based on the oligomerization of multiple copies of just one or a few types of structurally equivalent or quasiequivalent protein subunits (3, 4). However, even the most simple virion can accomplish many complex and sometimes conflicting functions during the infectious cycle (5). Virus capsids must be robust enough to protect the viral genome against physical-chemical assaults (6) but labile and͞or flexible enough to release the infectious nucleic acid into a target cell (7,8). Also, many virions accommodate a maximum amount of genetic information in the minimum space, as the nucleic acid is packed to crystal densities (9). To meet these and other stringent biological requirements, viral particles could have acquired outstanding mechanical properties, which are beginning to be revealed (10, 11). For example, it has been shown that on DNA packaging, the 29 and bacteriophage capsids can withstand internal pressures as high as 60 (12) and 20 (13) bars, respectively. Several studies have provided insights into the forces involved in DNA ejection from or packaging in phage capsids (14-16). A recent study of 29 empty capsids yielded a Young's modulus of 1.8 GPa (17), close to that of hard plastic. One of many important related aspects that have not been directly investigated yet is the influence of the enclosed genomic nucleic acid on the mechanical properties of the viral particle.The parvovirus minute virus of mice (MVM) is among ...

No abstract

No abstract

The sliding of a sharp nanotip on graphene completely immersed in water is investigated by molecular dynamics (MD) and atomic force microscopy. MD simulations predict that the atomic-scale stick-slip is almost identical to that found in ultrahigh vacuum. Furthermore, they show that water plays a purely stochastic role in sliding (solid-to-solid) friction. These observations are substantiated by friction measurements on graphene grown on Cu and Ni, where, oppositely of the operation in air, lattice resolution is readily achieved. Our results promote friction force microscopy in water as a robust alternative to ultra-high-vacuum measurements.