Viruses under mechanical force: Implications and applications.

Viruses are evolving biological entities whose perpetuation depends on their adaptive response to many selection pressures acting on them. Viruses are also solid objects that show some degree of deformability, brittleness, and strength when subjected to mechanical forces. Atomic force microscopy (AFM) allows the controlled application of mechanical force on individual virions, capsids, and viral components under close to physiological conditions. In this way, the structure, dynamics, and mechanical properties of virus particles, and their changes by the action of biologically relevant effectors, can be investigated at the single-particle level. AFM-based studies have shown that the mechanical properties of some viruses can have an adaptive value for virus survival, that mechanical forces are among the selection pressures some viruses may be confronted with, and that some viruses can exert mechanical forces that also constitute adaptive traits. AFM studies of viruses under mechanical force are also providing new insights into the relationships between virus structure and dynamics, physical properties, and biological function, even in those cases where natural mechanical forces may not be involved. The knowledge being acquired on virus biomechanics is contributing to understand virus biology and to the development of new biomedical or nanotechnological applications. The present review is addressed to a general readership of virologists, and attempts to summarize the results of over 20 years of studies that have used AFM, in combination with other biophysical, biochemical and/or biological approaches, to explore the connections between virus biology and mechanical force.