Structural Basis for Ni2+ Transport and Assembly of the Urease Active Site by the Metallochaperone UreE from Bacillus pasteurii

Abstract

Bacillus pasteurii UreE (BpUreE) is a putative chaperone assisting the insertion of Ni2+ ions in the active site of urease. The x-ray structure of the protein has been determined for two crystal forms, at 1.7 and 1.85 Å resolution, using SIRAS phases derived from a Hg 2+-derivative. BpUreE is composed of distinct N- and C-terminal domains, connected by a short flexible linker. The structure reveals the topology of an elongated homodimer, formed by interaction of the two C-terminal domains through hydrophobic interactions. A single Zn2+ ion bound to four conserved His-100 residues, one from each monomer, connects two dimers resulting in a tetrameric BpUreE known to be formed in concentrated solutions. The Zn2+ ion can be replaced by Ni2+ as shown by anomalous difference maps obtained on a crystal of BpUreE soaked in a solution containing NiCl2. A large hydrophobic patch surrounding the metal ion site is surface-exposed in the biologically relevant dimer. The BpUreE structure represents the first for this class of proteins and suggests a possible role for UreE in the urease nickel-center assembly.