Energy landscape remodeling mechanism of Hsp70-chaperone-accelerated protein folding

Jiajun Lu,Xiaoyi Zhang,Yichao Wu,Yuebiao Sheng,Wenfei Li,Wei Wang

doi:10.1016/j.bpj.2021.03.013

Jiajun Lu, Xiaoyi Zhang + Show 4 more

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https://doi.org/10.1016/j.bpj.2021.03.013

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Abstract

Hsp70 chaperone is one of the key protein machines responsible for the quality control of protein production in cells. Facilitating in vivo protein folding by counteracting misfolding and aggregation is the essence of its biological function. Although the allosteric cycle during its functional actions has been well characterized both experimentally and computationally, the mechanism by which Hsp70 assists protein folding is still not fully understood. In this work, we studied the Hsp70-mediated folding of model proteins with rugged energy landscape by using molecular simulations. Different from the canonical scenario of Hsp70 functioning, which assumes that folding of substrate proteins occurs spontaneously after releasing from chaperones, our results showed that the substrate protein remains in contacts with the chaperone during its folding process. The direct chaperone-substrate interactions in the open conformation of Hsp70 tend to shield the substrate sites prone to form non-native contacts, which therefore avoids the frustrated folding pathway, leading to a higher folding rate and less probability of misfolding. Our results suggest that in addition to the unfoldase and holdase functions widely addressed in previous studies, Hsp70 can facilitate the folding of its substrate proteins by remodeling the folding energy landscape and directing the folding processes, demonstrating the foldase scenario. These findings add new, to our knowledge, insights into the general molecular mechanisms of chaperone-mediated protein folding.

Highlights

Most of our current knowledge on protein folding has been accumulated based on in vitro biochemical studies, protein folding in cells often involves a more complicated microenvironment, such as molecular crowding and oxidative stress, which tends to increase the risk of misfolding and aggregation [1]
The molecular mechanisms of Hsp70-mediated protein folding have been the focus of recent efforts in protein folding studies
The canonical holdase and unfoldase mechanisms have been well characterized for Hsp70 [24,56], whether it can function as a foldase to directly assist the substrate folding is still in dispute [23,24,57,58], as it is challenging in experiment to precisely characterize the folding kinetics with the presence of direct chaperonesubstrate interactions

Summary

Introduction

Most of our current knowledge on protein folding has been accumulated based on in vitro biochemical studies, protein folding in cells often involves a more complicated microenvironment, such as molecular crowding and oxidative stress, which tends to increase the risk of misfolding and aggregation [1]. A large fraction of proteins cannot fold spontaneously without assistance from folding machines. Cells have evolved various kinds of chaperones to aid in robust folding in such complex environments and prevent nonproductive misfolding and aggregation, which is essential for the integrity of molecular events in the life cycle of cells [2,3,4,5,6]. Chaperone-mediated protein folding typically involves the steps of substrate exchange, co-chaperone binding and unbinding, ATP binding and hydrolysis, and allosteric motions of the chaperone molecules [7,8,9], which makes in vivo studies of protein folding much more difficult than that of spontaneous folding under dilute conditions. Accurate molecular mechanisms of how the molecular chaperones assist in vivo protein folding remain

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