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 microfluidics-magnetic-tweezers technology to apply physiological force pulses on client proteins, keeping the chaperones unperturbed. Interestingly, we observe that chaperones behave differently under force than its previously known functions. For instance, tunnel associated chaperones (trigger factor and DsbA), otherwise working as holdase without force, assist folding under force. This process generates an additional mechanical energy up to ~65 zJ to facilitate translation or translocation. However, other cytoplasmic oxidoreductases (PDI, thioredoxin) or well-known foldase chaperone (DnaKJE) does not possess this mechanical folding ability. Notably, the transferring chaperones (DnaK, DnaJ, SecB), act as unfoldase and slow down folding process 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.