  What can cells gain by using disordered, rather than folded, proteins in the
architecture of their skeleton? Disordered proteins take multiple co-existing
conformations, and often contain segments which act as random-walk-shaped
polymers. Using X-ray scattering we measure the compression response of
disordered protein hydrogels, which are the main stress-responsive component of
neuron cells. We find that at high compression their mechanics are dominated by
gas-like steric and ionic repulsions. At low compression, specific attractive
interactions dominate. This is demonstrated by the considerable hydrogel
expansion induced by the truncation of critical short protein segments.
Accordingly, the floppy disordered proteins form a weakly cross-bridged
hydrogel, and act as shock absorbers that sustain large deformations without
failure.
