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 coil determined to a resolution of 1.8 Angstrom using a combination of single isomorphous repl acement (SIR) and multi-wavelength anomalous diffraction (MAD). The overall structure of Hsc20 consists of two distinct domains, an N-terminal J-domai n 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 int eractions with Hsc66, resembles the sc-topology of J-domain fragments of Es cherichia coli DnaJ and human Hdj1 previously determined by solution NMR me thods. 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 coiled-coil. The two domains make contact through an extensi ve hydrophobic interface (similar to 650 Angstrom (2)) suggesting that thei r 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 rigi d scaffold to facilitate positioning of the protein substrates targeted to Hsc66. (C) 2000 Academic Press.