Fluctuating Non-linear Spring Model

Figure: AFM-based forced deformation of empty CCMV and TrV shell, TrV with ssRNA, and AdV with dsDNA. The average experimental spectra (data points) are compared with (solid) theoretical \(FX\)-curves.

Mechanical testing has become the main tool to probe the physico-chemical and materials properties of the protein shells of plant and animal viruses, and bacteriophages . A variety of viruses have been explored by profiling the indentation force \(F\) as a function of particle deformation \(X\) (\(FX\)-curve). These experiments reveal an amazing diversity of mechanical properties of biological particles; however, the experimental results are difficult to interpret without a theoretical modeling framework. What types of mechanical excitations drive the particle deformation and collapse? What determines the mechanical limit of the particle - the critical forces and critical deformations? Why are the \(FX\)-spectra weakly non-linear? Why do spectra for the same particle differ from one measurement to another? This points to the stochastic nature of collapse transitions, but what defines the likelihood of structural collapse at a given force load?

We developed a systematic approach for meaningful interpretation of the force-deformation spectral lineshapes available from single-particle nanomanipulation experiments. The theory links the slope, critical force, and the critical deformation of the \(FX\)-curve with the physical characteristics of the structure, geometry and overall shape of the particle and indenter. We identify the types of mechanical excitations, which contribute to the particle deformation (indentation) \(X\), by analyzing the structure output from the MD simulations of forced deformation of the CCMV particle. We formulate and apply the Fluctuating Nonlinear Spring model to characterize the \(FX\)-spectra for the CCMV, AdV and TrV particles obtained as described in Refs. [Snijder2013a], [Snijder2013b], [Snijder2012].

[Snijder2013a]

J. Snijder, V. S. Reddy, E. R. May, W. H. Roos, G. R. Nemerow and G. J. L. Wuite (2013) , W. H.”Integrin and defensin modulate the mechanical properties of adenovirus.” J. Virol. 87: 2756.

[Snijder2013b]

J. Snijder, C. Uetrecht, R. Rose, R. Sanchez, G. Marti, J. Agirre, D. M. Guerin, G. J. L. Wuite, A. J. R. Heck and W. H. Roos (2013) “Probing the biophysical interplay between a viral genome and its capsid.” Nat. Chem. 5: 502-509.

[Snijder2012]

J. Snijder, I. L. Ivanovska, M. Baclayon, W. H. Roos and G. J. L. Wuite (2012) “Probing the impact of loading rate on the mechanical properties of viral nanoparticles.” Micron 43: 1343-1350.