Optimal Prevention of Client-Protein Aggregation on the Surface of the Hsp70 Chaperone: A Computational Study

Abstract

Hsp70, also known as DnaK, is a class of E. Coli molecular chaperones essential for maintaining cell homeostasis. Along with its co-chaperones DnaJ and GrpE, Hsp70 facilitates de novo and in vivo protein folding thereby reducing protein aggregation. This chaperone cycle has been studied extensively,though the exact type of interactions during protein folding between the chaperone and the client protein and whether that plays a significant role in reducing client protein aggregation remains unknown. We employed the previously published CHAMP70 and aggregation computational models to simulate both the interaction of the client protein with the Hsp70 chaperone cycle and client-protein aggregation pathway proceeding via an obligatory misfolded monomer (M∗). Our simulations focused on whether the client protein folds in solution after being released from the chaperone or folds directly on the chaperone while still bound as well as if having a high kinetic barrier between the transition of unfolded protein to M∗ plays a role in protein folding in the presence of a chaperone. Most notably, we found that in situations where there is a high kinetic barrier then folding on the chaperone reduced the t ½ of aggregation from 37 days to 2314 days, a 98% difference. We also simulated various client protein affinities, rates of M∗ nucleation, and client-protein/chaperone ratios to determine ideal situations where folding on the chaperone is favored and when folding off the chaperone is favored. Our result implies that Hsp70 is most efficient as a molecular chaperone when it folds the client substrate still bound to its surface.