W0391

1.6-Å Crystal Structure of the Class of Chaperones Represented by E. coli Hsp31 Reveals a Putative Catalytic Triad. Paulene M. Quigley*, Konstantin Korotkov§, François Baneyx¶, and Wim G.J. Hol*||, *Biomolecular Structure Center, P.O. Box 357742, Univ. of Washington, Seattle, WA 98195, §Dept. of Biochemistry, P.O. Box 357742, Univ. of Washington, Seattle, WA 98195, ¶Dept. of Chemical Engineering, P.O. Box 351750, Univ. of Washington, Seattle, WA 98195, and ||Howard Hughes Medical Inst., Univ. of Washington, Seattle, WA 98105.

Heat shock proteins play essential protective roles under stress conditions by preventing the formation of protein aggregates and degrading misfolded proteins. EcHsp31, the yedU (hchA) gene product, is a representative member of a novel family of chaperones that alleviates protein misfolding by interacting with early unfolding intermediates. The 1.6-Å crystal structure of the EcHsp31 dimer reveals a system of hydrophobic patches, canyons, and grooves, which may stabilize partially unfolded substrate. The presence of a well conserved, yet buried, triad in each two-domain subunit suggests a still unproven hydrolytic function of the protein. A flexible extended linker between the A and P domains may play a role in conformational flexibility and substrate binding. The α-β sandwich of the EcHsp31 monomer shows structural similarity to PhPI, a protease belonging to the DJ-1 superfamily. The structure-guided sequence alignment indicates that Hsp31 homologs can be divided in three classes based on variations in the P domain that dramatically affect both oligomerization and catalytic triad formation.