High-resolution solution structure of the 18 kDa substrate-binding domain of the mammalian chaperone protein Hsc70

Abstract

The three-dimensional structure for the substrate-binding domain of the mammalian chaperone protein Hsc70 of the 70 kDa heat shock class (HSP70) is presented. This domain includes residues 383–540 (18 kDa) and is necessary for the binding of the chaperone with substrate proteins and peptides. The high-resolution NMR solution structure is based on 4150 experimental distance constraints leading to an average root-mean-square precision of 0.38 Å for the backbone atoms and 0.76 Å for all atoms in the beta-sandwich sub-domain. The protein is observed to bind residue Leu539 in its hydrophobic substrate-binding groove by intramolecular interaction. The position of a helical latch differs dramatically from what is observed in the crystal and solution structures of the homologous prokaryotic chaperone DnaK. In the Hsc70 structure, the helix lies in a hydrophobic groove and is anchored by a buried salt-bridge. Residues involved in this salt-bridge appear to be important for the allosteric functioning of the protein. A mechanism for interdomain allosteric modulation of substrate-binding is proposed. It involves large-scale movements of the helical domain, redefining the location of the hinge area that enables such motions.