Direct observation of the mechanical role of bacterial chaperones in protein folding

Protein folding under force is an integral source of generating mechanical energy in various cellular processes, ranging from protein translation to degradation. Although chaperones are well known to interact with proteins under mechanical force, how they respond to force and control cellular energetics remains unknown. To address this question, we introduce novel real-time magnetic-tweezers technology to mimic physiological force environment on client proteins, keeping the chaperones unperturbed. We studied two structurally distinct client proteins with seven different chaperones, independently and in combination, and proposed novel mechanical activity of chaperones. We found chaperones behave differently, while these client proteins are under force than its previously known functions. For instance, tunnel associated chaperones (DsbA and trigger factor), otherwise working as holdase without force, assist folding under force. This process generates an additional mechanical energy up to ~147 zJ to facilitate translation or translocation. However, well-known cytoplasmic foldase chaperones (PDI, thioredoxin, or DnaKJE), does not possess the mechanical folding ability under force. Notably, the transferring chaperones (DnaK, DnaJ, SecB), act as unfoldase and slow down folding process, both in the presence and absence of force, to prevent misfolding of the client proteins. This provides an emerging insight of mechanical roles of chaperones: they can generate or consume energy by shifting energy landscape of the client proteins towards folded or unfolded state; suggesting an evolutionary mechanism to minimize the energy consumption in various biological processes.