Material Properties of Viral Nanocages Explored by Atomic Force Microscopy

Abstract

Single-particle nanoindentation by atomic force microscopy (AFM) is an emergent technique to characterize the material properties of nano-sized proteinaceous systems. AFM uses a very small tip attached to a cantilever to scan the surface of the substrate. As a result of the sensitive feedback loop of AFM, the force applied by the tip on the substrate during scanning can be controlled and monitored. By accurately controlling this scanning force, topographical maps of fragile substrates can be acquired to study the morphology of the substrate. In addition, mechanical properties of the substrate like stiffness and breaking point can be determined by using the force spectroscopy capability of AFM. Here we discuss basics of AFM operation and how this technique is used to determine the structure and mechanical properties of protein nanocages, in particular viral particles. Knowledge of morphology as well as mechanical properties is essential for understanding viral life cycles, including genome packaging, capsid maturation, and uncoating, but also contributes to the development of diagnostics, vaccines, imaging modalities, and targeted therapeutic devices based on viruslike particles.

Quantification and modification of the equilibrium dynamics and mechanics of a viral capsid lattice self-assembled as a protein nanocoating

“…[30][31][32] In turn, the emerging area of mechanical virology is providing novel insights into properties of virus particles such as elasticity, brittleness and material fatigue, discovering the structural determinants of these properties, and revealing biological adaptations based on mechanical features. [35][36][37][38][39][40][41][42][43][44][45][46][47] Linkages between propensity for structural rearrangements and mechanical elasticity of virus particles are also being uncovered. 40,46 Here, the capsid protein of human immunodeficiency virus (HIV) has been used as a model to investigate and manipulate the still largely unknown mechanics and equilibrium dynamics of protein-based 2-D materials organized at the nanoscale.…”

Mechanical Characterization of Liposomes and Extracellular Vesicles, a Protocol

“…Nanoindentation is an established technique to get quantitative information about the mechanical properties of nanoparticles (Rosmalen et al, 2015 ; Marchetti et al, 2016 ). Here, we use a similar approach for vesicle indentations (see Figure 1C for a schematic representation).…”

Structural determinants of mechanical resistance against breakage of a virus-based protein nanoparticle at a resolution of single amino acids

“…In recent years, investigation of the mechanical properties of virus particles has been enabled by the development of both theoretical approaches including coarse-grained molecular dynamics (MD) simulations, [30][31][32][33][34][35][36][37][38][39][40] and experimental singlemolecule techniques such as atomic force microscopy (AFM) under near-physiological conditions. [26][27][28][29][41][42][43] In particular, our group is using AFM to provide insights into the relationships between the fine structure of model virus particles, their mechanical properties, and their function. [44][45][46][47][48][49][50] By exploring the effects on a certain mechanical property (such as stiffness) of small structural alterations in the virus particle by single mutations introduced by protein engineering, knowledge about the specific chemical groups and interactions that determine that property can be acquired.…”