Cochaperones enable Hsp70 to use ATP energy to stabilize native proteins out of the folding equilibrium

Huafeng Xu

doi:10.1038/s41598-018-31641-w

Abstract

The heat shock protein 70 (Hsp70) chaperones, vital to the proper folding of proteins inside cells, consume ATP and require cochaperones in assisting protein folding. It is unclear whether Hsp70 can utilize the free energy from ATP hydrolysis to fold a protein into a native state that is thermodynamically unstable in the chaperone-free equilibrium. Here I present a model of Hsp70-mediated protein folding, which predicts that Hsp70, as a result of differential stimulation of ATP hydrolysis by its Hsp40 cochaperone, dissociates faster from a substrate in fold-competent conformations than from one in misfolding-prone conformations, thus elevating the native concentration above and suppressing the misfolded concentration below their respective equilibrium values. Previous models would not make or imply these predictions, which are experimentally testable. My model quantitatively reproduces experimental refolding kinetics, predicts how modulations of the Hsp70/Hsp40 chaperone system affect protein folding, and suggests new approaches to regulating cellular protein quality.

Highlights

The discovery of chaperones and their roles in assisting protein folding amended the long-held view that proteins spontaneously fold into their native structures[1,2,3]
It was demonstrated that chaperones such as GroEL and Hsp[70] depend on continuous ATP hydrolysis to maintain a protein in a native state that is thermodynamically unstable[13], but it is unknown how Hsp[70] can utilize the ATP free energy to alter the folding equilibrium
It is unclear whether Hsp[70] can use the free energy from ATP hydrolysis to drive its substrate protein toward the native state, N, and away from the misfolded state, M, such that fN/fM > fN,eq/fM,eq, where fS is the fraction of the substrate in state S at the steady state of heat shock protein 70 (Hsp70)-mediated folding, and fS,eq is the corresponding fraction at the folding equilibrium in the absence of the chaperone

Summary

Introduction

The discovery of chaperones and their roles in assisting protein folding amended the long-held view that proteins spontaneously fold into their native structures[1,2,3]. It is unclear whether Hsp[70] can use the free energy from ATP hydrolysis to drive its substrate protein toward the native state, N, and away from the misfolded state, M, such that fN/fM > fN,eq/fM,eq, where fS is the fraction of the substrate in state S at the steady state of Hsp70-mediated folding, and fS,eq is the corresponding fraction at the folding equilibrium in the absence of the chaperone.

Results

Conclusion