Remaut H, Safarov N, Ciurli S, Van Beeumen J
Laboratory of Protein Biochemistry and Protein Engineering, Ghent University, K. L. Ledeganckstraat 35, B-9000 Gent, Belgium.
J Biol Chem. 2001 Dec 28;276(52):49365-70. doi: 10.1074/jbc.M108304200. Epub 2001 Oct 15.
Bacillus pasteurii UreE (BpUreE) is a putative chaperone assisting the insertion of Ni(2+) 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 A 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 Zn(2+) 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 Zn(2+) ion can be replaced by Ni(2+) as shown by anomalous difference maps obtained on a crystal of BpUreE soaked in a solution containing NiCl(2). 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.
巴氏芽孢杆菌脲酶E（BpUreE）是一种假定的伴侣蛋白，可协助镍离子（Ni²⁺）插入脲酶的活性位点。利用从汞（Hg²⁺）衍生物获得的单波长反常散射（SIRAS）相位，已确定了该蛋白两种晶体形式的X射线结构，分辨率分别为1.7 Å和1.85 Å。BpUreE由不同的N端和C端结构域组成，通过一个短的柔性连接子相连。该结构揭示了一种细长同型二聚体的拓扑结构，它是由两个C端结构域通过疏水相互作用形成的。一个与四个保守的组氨酸-100残基（每个单体一个）结合的单个锌离子（Zn²⁺）连接两个二聚体，形成已知在浓缩溶液中形成的四聚体BpUreE。如在浸泡于含有氯化镍（NiCl₂）溶液中的BpUreE晶体上获得的反常差值图所示，锌离子（Zn²⁺）可被镍离子（Ni²⁺）取代。在生物学相关的二聚体中，围绕金属离子位点的一个大的疏水区域暴露于表面。BpUreE结构代表了这类蛋白质中的首个结构，并暗示了UreE在脲酶镍中心组装中的可能作用。
