Ye Jun, Kandegedara Ashoka, Martin Philip, Rosen Barry P
Department of Biochemistry and Molecular Biology, Wayne State University, School of Medicine, 540 E. Canfield Ave., Detroit, MI 48201, USA. .
J Bacteriol. 2005 Jun;187(12):4214-21. doi: 10.1128/JB.187.12.4214-4221.2005.
The Staphylococcus aureus plasmid pI258 cadCA operon encodes a P-type ATPase, CadA, that confers resistance to the heavy metals Cd(II), Zn(II), and Pb(II). Expression of this heavy-metal efflux pump is regulated by CadC, a homodimeric repressor that dissociates from the cad operator/promoter upon binding of Cd(II), Pb(II), or Zn(II). CadC is a member of the ArsR/SmtB family of metalloregulatory proteins. Here we report the X-ray crystal structure of CadC at 1.9 angstroms resolution. The dimensions of the protein dimer are approximately 30 angstroms by 40 angstroms by 70 angstroms. Each monomer contains six alpha-helices and a three-stranded beta-sheet. Helices 4 and 5 form a classic helix-turn-helix motif that is the putative DNA binding region. The alpha1 helix of one monomer crosses the dimer to approach the alpha4 helix of the other monomer, consistent with the previous proposal that these two regulatory metal binding sites for the inducer cadmium or lead are each formed by Cys-7 and Cys-11 from the N terminus of one monomer and Cys-58 and Cys-60 of the other monomer. Two nonregulatory metal binding sites containing zinc are formed between the two antiparallel alpha6 helices at the dimerization interface. This is the first reported three-dimensional structure of a member of the ArsR/SmtB family with regulatory metal binding sites at the DNA binding domain and the first structure of a transcription repressor that responds to the heavy metals Cd(II) and Pb(II).
金黄色葡萄球菌质粒pI258的cadCA操纵子编码一种P型ATP酶CadA，它赋予对重金属镉（II）、锌（II）和铅（II）的抗性。这种重金属外排泵的表达受CadC调控，CadC是一种同二聚体阻遏物，在结合镉（II）、铅（II）或锌（II）后会从cad操纵子/启动子上解离。CadC是金属调节蛋白ArsR/SmtB家族的成员。在此我们报告了分辨率为1.9埃的CadC的X射线晶体结构。该蛋白质二聚体的尺寸约为30埃×40埃×70埃。每个单体包含6个α螺旋和一个三链β折叠。螺旋4和螺旋5形成一个经典的螺旋-转角-螺旋基序，这是推测的DNA结合区域。一个单体的α1螺旋穿过二聚体接近另一个单体的α4螺旋，这与之前的提议一致，即诱导剂镉或铅的这两个调节性金属结合位点分别由一个单体N端的Cys-7和Cys-11以及另一个单体的Cys-58和Cys-60形成。在二聚化界面处的两个反平行α6螺旋之间形成了两个含锌的非调节性金属结合位点。这是首次报道的ArsR/SmtB家族成员在DNA结合结构域具有调节性金属结合位点的三维结构，也是首个对重金属镉（II）和铅（II）作出反应的转录阻遏物的结构。
