TCB Publications - Abstract

Wouter H. Roos, Melissa M. Gibbons, Anton Arkhipov, Charlotte Uetrecht, Norman Watts, Paul Wingfield, Alasdair C. Steven, Albert J.R.Heck, Klaus Schulten, William S. Klug, and Gijs J.L. Wuite. Squeezing protein shells: how continuum elastic models, molecular dynamics simulations and experiments coalesce at the nanoscale. Biophysical Journal, 99:1175-1181, 2010. (PMC: 2920642)

ROOS2010 The rapid current growth in the use of nano-sized particles is fuelled, in part, by improved understanding and manipulability of their physical properties which are essential for achieving optimal functionality. Here we report detailed quantitative measurements of the mechanical response of nano-sized protein shells - viral capsids - to large-scale physical deformations and compare them with theoretical descriptions from continuum elastic modelling and molecular dynamics (MD). Specifically, we used nanoindentation by atomic force microscopy (AFM) to investigate the complex elastic behaviour of Hepatitis B virus capsids. These capsids are hollow,  30nm in diameter, and conform to icosahedral (5-3-2) symmetry. First we show that their indentation behaviour, which is symmetry axis-dependent, cannot be reproduced by a simple model based on Föppl-von Kármán thin-shell elasticity with the 5-fold vertices acting as pre-stressed disclinations. However, we can properly describe the measured non-linear elastic and orientation-dependent force response with a 3D topographically detailed finite-element model. Next, we show that coarse-grained MD simulations also yield good agreement with our nanoindentation measurements, even without any fitting of force field parameters in the MD model. This study demonstrates that material properties of viral nanoparticles can be correctly described by both modelling approaches. At the same time, we show that even for large deformations it suffices to approximate the mechanical behaviour of nano-sized viral shells with a continuum approach, ignoring specific molecular interactions. This experimental validation of continuum elastic theory provides an example of how rules of macroscopic physics can apply to nanoscale molecular assemblies.

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