Fig. 1.

(A) The experimental structure of E. coli Hsp70 chaperone (DnaK) in the ADP-bound state (2KHO).⁹ The substrate-binding domain (SBD) is on the top and the nucleotide-binding domain (NBD) is on the bottom of the picture. The C-terminal three-helix bundle (SBD-α; E509-Q603) part of the substrate binding domain is packed to the β-sandwich part (SBD-β; V394-N508). The subdomains of NBD^5,6 are: Ia (residues I4-P37, P112-D182, and K363-T383), Ib (residues S38-A111), IIa (residues K183-L227 and D311-R362), and IIb (residues G228-E310). Subdomains Ia and Ib constitute subdomain NBD-I, of which they are the upper and lower lobes, respectively, and subdomains IIa and IIb constitute subdomain NBD-II of which they are the upper and lower lobe, respectively. The distances which were monitored experimentally¹¹ are marked by white dashed lines and the corresponding residues are labeled; they are identified with the distances between SBD-β and SBD-α (N458···T563), between NBD-II and SBD-β (E318···V425) and between NBD-I and SBD-α (G132···A523). L denotes the linker between NBD and SBD. Helix A+B (which is split into parts A and B in DnaK) denotes the N-terminal α-helix of SBD-α. (B) The experimental structure of yeast Sse1 ATP-bound Hsp110 co-chaperone (3C7N),⁸ highly homologous to Hsp70, which has the Hsc70 chaperone bound to the substrate-binding domain between SBD-β and SBD-α, which is a putative model of the SBD-open conformation of Hsp70s. The ADP-bound Hsc70 ligand of Hsp110 has been removed from the picture for clarity. The structure of ATP-bound Hsp110 shown in panel B can be considered as a plausible model of ATP-bound Hsp70. The drawings were done with PyMOL (http://www.pymol.org). The ribbons are colored blue to red from the N- to the C-terminus.