Grains and glasses, two widely different materials, arrest their inter-particle motions upon a decrease in temperature and, respectively, external load in ways that share common phenomenology and that hint at the existence of a unified jamming phase diagram.  However, theories for the common behavior are lacking, mainly because of the disparate nature of the interactions between the macroscopic grains vs. that between atoms. The disparity also resulted, so far, in a lack of examples of real systems in which both temperature and force-jamming can manifest together. Here, by using temperature- and force-unfolding molecular dynamics simulations, we demonstrate that folded proteins exhibit a signature common to both glassiness and jamming: upon folding, they develop a peak in the interatomic force distributions. Then, employing experimentally measured forces on jammed grains and droplets, we show that, remarkably, when scaled by the average force, these distributions fall on the same, universal peak with that for the simulated proteins, despite the nine orders of magnitude difference in the characteristic forces at play in proteins vs. grains. We also show that this peak --a subtle static signature of an otherwise dynamical transition-- can be used to rank proteins according to their resilience to unfolding.  We also reveal a dynamical signature of jamming in the form of a dramatic slow-down of stress relaxation of the proteins in the folded or collapsed state, akin to the relaxation slow-down in jammed granular matter. Our results have implication for the design of stable biopolymers and lead to a view of protein folding inducing self-organization of stress propagating paths, or force chains, across the protein tertiary structure. Reference: P. P. Jose and I. Andricioaei, Similarities beween protein folding and granular jamming, Nature Communications, 3 , 1161 (2012).

Protein folding exhibits universal signatures of granular jamming

245th National Meeting (2013)

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