Trigger Factor Boosts the Work Done by Protein Folding under Force

Abstract

Protein folding under force generates mechanical work, which is integral to several biological processes including muscle contraction, proteasomal degradation, and protein translation. As molecular chaperones affect protein folding, we hypothesized that chaperones would modulate the mechanical work generated from protein folding. Trigger Factor (TF) is a model chaperone from E. coli, which is found intracellularly in both ribosome-associated and free cytosolic states. Here, we apply Magnetic Tweezers-based single molecule force spectroscopy to investigate the effect of TF in the mechanical folding of a substrate, protein L (PL). We find that TF increases the folding probability by up to 40% at ∼8 pN. The half-maximal TF activity, K1/2, is highly force dependent, ranging from 0.6 µM at 6.2 pN to 27.5 µM at 8.9 pN. The functional consequence of this TF-assisted mechanical folding is an increase in the effective work generated, calculated as the product of the force, the PL folding contraction length, and the TF-dependent folding probability. The maximal activity of TF (at 10 µM and 8.4 pN) contributes 40 zJ to the work done by protein folding, comparable to the energy delivered by myosin motors. 85% of the mechanical contribution from TF is achieved between 500 nM and 2 μM TF, in the range of the chaperon's cellular concentration. This is the first study of the influence of a molecular chaperone in the work done by protein folding, which could have important consequences in the translation process, helping polypeptide synthesis and assisting protein folding under force.