“A protein that acts like a paper ball: Glassy dynamics and memory effects in the single-molecule mechanics of a disordered protein”
Disordered proteins display an intriguing mix of entropic freedom and weak transient interactions that underlie their biological roles. Motivated to understand that interplay, and building upon our group’s experience in using polymer elasticity to gain insight into polymeric structure and behavior, we carried out single-molecule stretching measurements on a model disordered protein construct. We particularly measured the response of the construct to sudden changes in applied tension. Unexpectedly, we found that the construct displays a glassy mechanical response: a one-step change in the applied force causes a slow, logarithmic response in the chain extension. Further, the disordered chain exhibits a distinct memory effect (the Kovacs effect), in which the chain ‘remembers’ changes in force that occurred tens of seconds prior. To interpret these findings, we turned to recent studies that showed similar dynamics in a completely different system—the slow dynamics of crumpled paper balls. I will discuss how the insight from crumpled paper gave us clues into the molecular processes at work in the protein system, ultimately revealing that the mechanisms of kinetics in the disordered chain differ from those typically invoked to explain glassy behavior in structured proteins.