Structural studies of the YedU stress protein
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The knowledge of stress proteins is important for understanding stress response, pathology of a broad set of diseases, and the development of therapeutics. The Escherichia coli YedU stress protein, also known as Hsp31, is highly induced upon heat shock. To obtain a better understanding for the possible molecular function of the YedU stress protein, it was expressed, purified, and crystallized. The crystal structure of YedU was determined at 2.2 Å resolution in a multiple isomorphous replacement (MIR) experiment. \r\nYedU monomer has an alpha/beta/alpha sandwich domain and a second smaller domain. Between the sandwich domain and the second smaller domain, there is a putative catalytic triad composed of Cys184, His185, and Asp213. A metal-binding site was identified, where a zinc(II) ion is coordinated by a 2-His-1-carboxylate motif composed of His85, Glu90, and His122. The possible functions of the metal-binding site and the Cys184-His185-Asp213 triad are discussed. \r\nIt was reported that YedU has chaperone activity in vitro. YedU forms dimers in solution and the dimer interface was identified. The molecular surface of the YedU homodimer exhibits a number of solvent-exposed hydrophobic patches that are reminiscent of substrate-binding sites of molecular chaperones. To investigate the role of a central hydrophobic patch in substrate binding, four mutants were made, each replacing a hydrophobic residue with a charged residue. Compared with the wild type YedU protein, the chaperone activity of these mutants was only slightly reduced, suggesting that these residues alone do not play a dominant role in substrate binding at high temperatures.