Nature Commun. 3, 1161 (2012)

Credit: © 2012 NPG

Vigorously shake a pack of grains that are stuck, and they will 'unjam'. Heat a glass to a sufficiently high temperature, and it will flow. These apparently disconnected behaviours are usually expressed as a universal jamming phase diagram that depends on temperature, density and external force. Now, Prasanth Jose and Ioan Andricioaei show that the mechanical behaviour of folded proteins is similar to that of granular materials and glasses. Using molecular dynamics simulations, the researchers pulled the ends of protein chains in their native states, or increased the temperature. They found that the distribution of normalized forces per protein atom in the resulting trajectories fell on a universal shape (with a characteristic peak at low forces) common to force distributions measured on jammed grains and droplets. They also show that the stress relaxation of folding proteins slows down with respect to that of unfolded ones, a dynamic signature resembling the viscous slowdown of jammed grains and glasses. These results suggest that protein folding can be mechanically interpreted as a jamming transition.