The Mechanical Roles of Chaperons

Protein folding under force is an integral source of generating mechanical power to carry out diverse cellular functions. Though chaperones interact with proteins throughout the different stages of folding pathways, how they behave and interact with client proteins under force was not known. Here we introduce the mechanical role of chaperone and explained it with seven independent chaperones using single molecule based real-time microfluidics-magnetic-tweezers. We showed and quantified how chaperones increase or decrease mechanical work output by shifting the folding energy landscape of the client proteins towards the folded or unfolded state. Notably, we found chaperones could behave differently under force. For instance: trigger factor, ribosomal-tunnel associated chaperone, working as a holdase in absence of force, but assist folding under force. This phenomenon generates extra mechanical energy to pull the polyprotein from the stalled ribosome. This is also relevant for SecYEG tunnel associated oxidoreductase DsbA, which act similarly like TF and increases the mechanical energy up to ~59 zJ, to facilitate membrane translocation in an energy efficient manner. However cytoplasmic oxidoreductases such as PDI and Thioredoxin, unlike DsbA, do not have the mechanical folding ability. Interestingly, we observed a highly potential foldase-DnaKJE chaperone complex, only restores the folding ability of the client protein and fails to act like TF or DsbA under force. However, the individual components of this complex, DnaK or DnaJ, act as a mechanical holdase and inhibits folding; similar to that of SecB. Together our study provides an emerging insight of mechanical chaperone behavior, where tunnel associated chaperones generate extra mechanical work whereas the cytoplasmic chaperones are unable to generate that, which might have evolved to minimize the energy consumption in biological processes.