ATP HYDROLYSIS MECHANISM OF THE HSP70 CHAPERONE PROTEIN

Abstract

Hsp70 is a 70 kDa chaperone protein which consist of a 45 kDa N-terminal ATPase domain and a 25 kDa C-terminal substrate binding domain [1]. A linker containing a conserved VLLL sequence connects the two domains and functions in allosteric communication between them [2]. When ATP is bound, the affinity of Hsp70 to substrates, which are misfolded proteins, is low. Upon substrate binding, ATP is hydrolyzed into ADP and the affinity to the substrate increases. Exchange of ADP with an ADP causes the release of the substrate and the new turnover begins [1]. In this study, N-terminal ATPase domain is studied to determine the ATP hydrolysis mechanism of the protein. QM/MM ONIOM method with M062X for QM level and AMBER force field for the MM level is used in this study. In general, phosphate hydrolysis reactions can take place either through an associative or a dissociative mechanism depending on the environment. Therefore, both mechanisms are tested in order to identify lowest energy pathway [3]. Some amino acids in the active site may potentially act in acid/base catalysis. To test this hypothesis, proton transfer from K70, D194 or D201 to ATP is investigated.