Synopsis: Protein Shells Take a Strength Test

The protein shells surrounding large viruses have built-in tension that determines their shapes.
Synopsis figure
W. S. Klug et al., Phys. Rev. Lett. (2012)

To protect their genetic material, viruses surround themselves with a protein shell called a capsid. Most capsids have an icosahedral symmetry (like a 20-faced die), but large icosahedral capsids have a more faceted shape than smaller ones. As reported in Physical Review Letters, experiments in which viral capsids were poked with an atomic force microscope (AFM) confirm a decade-old prediction for why large icosahedral capsids are so faceted.

The fivefold symmetry of each vertex in an icosahedral capsid is geometrically mismatched with the sixfold symmetry of its surroundings, which creates a built-in tension or “pre-stress.” In 2003, researchers used elasticity theory to show that, because of this pre-stress, capsids larger than a critical diameter should buckle at their vertices, making them more faceted in shape. But elasticity theory is applicable to continuous materials, while capsids are made of discrete protein units, so it wasn’t clear if the predictions would apply to real viruses.

William Klug at the University of California, Los Angeles, and his colleagues took an indirect approach to measuring pre-stress in capsids. With the sensitive tip of an AFM, they measured the force needed to collapse the capsids of herpes simplex virus (a large virus) and found this force was larger if the capsid was intact, compared to if it had holes (missing proteins) at its vertices.

Klug et. al. argue that the pre-stress model is needed to explain the greater stiffness of the intact capsids. The group’s results agree well with predictions based on elasticity theory, suggesting the theory does apply to macromolecular assembly. – Jessica Thomas


Announcements

More Announcements »

Subject Areas

Biological Physics

Previous Synopsis

Semiconductor Physics

Asymmetry in Mobility

Read More »

Next Synopsis

Astrophysics

Solar Down Time

Read More »

Related Articles

Synopsis: Evolving Efficient Networks
Biological Physics

Synopsis: Evolving Efficient Networks

A new model shows that tissue growth is crucial for explaining the formation of hierarchical and optimized vascular networks, such as those seen in plants and animals. Read More »

Focus: Biological Cells Form Electric Circuits
Biological Physics

Focus: Biological Cells Form Electric Circuits

Cells that are electrically active and that also produce light for easy voltage monitoring could lead to new studies of heart arrhythmias and possibly bio-computing. Read More »

Synopsis: Bacteria Create Own Swim Lane
Biological Physics

Synopsis: Bacteria Create Own Swim Lane

Researchers calculate the size of a low-resistance buffer zone created by microbial organisms as they swim through the mucus lining of the stomach. Read More »

More Articles