Molecular dynamics study of the mechanism of the client unfolded protein delivery from HSP40 to HSP70.

Abstract

Heat Shock Protein (HSP) 70 is one of the molecular chaperones that supports protein folding. HSP70 is attracting attention as a target for drug discovery because of its involvement in cancer, neurodegenerative diseases, and so on. HSP70 consists of the nucleotide-binding domain (NBD) and the substrate-binding domain (SBD), with a flexible-linker region between the NBD and SBD. The SBD has two regions, SBD-α, which contains alpha-helices, and SBD-β, which contains beta-sheets. In the HSP70 chaperone cycle, unfolded client proteins are delivered by a J-domain protein (JDP), such as a co-chaperone HSP40. The J-domain in the JDP binds to the ATP-bound HSP70 state when the substrate is delivered to HSP70. After that, the JDP stimulates the ATP hydrolysis of HSP70, and the conformational change to the ADP-bound HSP70 form. Then the HSP70 helps the client protein folding with the nucleotide exchange factor molecular cooperation. However, the complex structure of JDP and HSP70 has not been solved, and the mechanism of substrate transfer has not been in detail yet. In this research, to clarify the mechanism of the substrate transfer process from HSP40 to HSP70, we performed molecular dynamics simulations of HSP40, HSP70, and HSP70 with the J-domain. J-domain in the HSP40 has two forms, open and closed. We modeled the complex structure of JDP and HSP70 using the open form of the HSP40. We found that SBD-β of HSP70 locates between two J-domains of HSP40, and HSP40 fluctuates. Therefore, the SBD-β would scoop the substrate that binds to the HSP40. Also, we found that the J-domain binding induced the fluctuations around the ATP binding site and the substrate-binding site from the simulation of HSP70 and the J-domain complex structure.