Molecular dynamics simulations shows real-time lid opening in Hsp70 chaperone

The stress-inducible mammalian heat shock protein Hsp70 and its bacterial orthologue DnaK are highly conserved molecular chaperones and a crucial part of the machinery responsible for protein folding and homeostasis. Hsp70 is a three-domain, 70 kDa protein that cycles between an ATP-bound state in which all three domains are securely coupled into one unit and an ADP-bound state in which they are loosely attached via a flexible interdomain linker. The Hsp70 presents an alluring novel therapeutic target since it is crucial for maintaining cellular proteostasis and is particularly crucial to cancer cells. We have performed molecular dynamics simulations of the SBD (substrate binding domain) along with the Lid domain in response to experimental efforts to identify small molecule inhibitors that impair the functioning of Hsp70. Our intent has been to characterize the motion of the SBD/Lid allosteric machinery and in, addition, to identify the effect of the PET16 molecule on this motion. Interestingly, we noticed the opening of the entire Lid domain in the apo-form of the dimer. The configuration of the open structure was very different from previously published structures (PDB 4JN4) of the open and docked conformation of the ATP bound form. MD simulations revealed the Lid to be capable of far greater dynamical excursions than has been anticipated by experimental structural biology. This is of value in future drug discovery efforts targeted to modulating Hsp70 activity. The PET16 molecule appears to be weakly bound and its effect on the dynamics of the complex is yet to be elucidated.