Crystal structure of Hsc20, a J-type co-chaperone from Escherichia coli

Hsc20 is a 20 kDa T-protein that regulates the ATPase activity and peptide-binding specificity of Hsc66, an hsp70-class molecular chaperone. We report herein the crystal structure of Hsc20 from Escherichia coli determined to a resolution of 1.8 Angstrom using a combination of single isomorphous replacement (SIR) and multi-wavelength anomalous diffraction (MAD). The overall structure of Hsc20 consists of two distinct domains, an N-terminal J-domain containing residues 1-75 connected by a short loop to a C-terminal domain containing residues 84-171. The structure of the J-domain, involved in interactions with Hsc66, resembles the sc-topology of J-domain fragments of Escherichia coli DnaJ and human Hdj1 previously determined by solution NMR methods. The C-terminal domain, implicated in binding and targeting proteins to Hsc66, consists of a three-helix bundle in which two helices comprise an anti-parallel colied-coli. The two domains make contact through an extensive hydrophobic interface (similar to 650 Angstrom (2)) suggesting that their relative orientations are fixed. Thus, Hsc20, in addition to its role in the regulation of the ATPase activity of Hsc66, may also function as a rigid scaffold to facilitate positioning of the protein substrates targeted to Hsc66. (C) 2000 Academic Press.