Nanoindentation of virus capsids in a molecular model

TL;DR

This study uses a molecular model to analyze the mechanical response of virus capsids during nanoindentation, revealing detailed structural behaviors and differences from continuum models, especially in stiffness and rupture mechanisms.

Contribution

It introduces a molecular-level model for virus capsid nanoindentation, capturing structural details and predicting behaviors not seen in continuum models.

Findings

Molecular model shows higher stiffness for CPMV than CCMV.

Irreversible bond rupture occurs in molecular model during indentation.

Continuum models exhibit buckling, while molecular models show bond rupture.

Abstract

A molecular-level model is used to study the mechanical response of empty cowpea chlorotic mottle virus (CCMV) and cowpea mosaic virus (CPMV) capsids. The model is based on the native structure of the proteins that consitute the capsids and is described in terms of the C-alpha atoms. Nanoindentation by a large tip is modeled as compression between parallel plates. Plots of the compressive force versus plate separation for CCMV are qualitatively consistent with continuum models and experiments, showing an elastic region followed by an irreversible drop in force. The mechanical response of CPMV has not been studied, but the molecular model predicts an order of magnitude higher stiffness and a much shorter elastic region than for CCMV. These large changes result from small structural changes that increase the number of bonds by only 30% and would be difficult to capture in continuum models. Direct comparison of local deformations in continuum and molecular models of CCMV shows that the molecular model undergoes a gradual symmetry breaking rotation and accommodates more strain near the walls than the continuum model. The irreversible drop in force at small separations is associated with rupturing nearly all of the bonds between capsid proteins in the molecular model while a buckling transition is observed in continuum models.