3f72
Crystal Structure of the Staphylococcus aureus pI258 CadC Metal Binding Site 2 Mutant
Structural highlights
FunctionCADC_STAAU Metal-binding repressor for the cad operon. Involved in resistance to heavy metals, such as cadmium, bismuth, zinc or lead. Binds 2 metal ions per subunit. Metal binding to the N-terminal regulatory site causes the repressor to dissociate from the DNA.[1] [2] [3] [4] [5] Evolutionary Conservation Check, as determined by ConSurfDB. You may read the explanation of the method and the full data available from ConSurf. Publication Abstract from PubMedThe Staphylococcus aureus plasmid pI258 cadCA operon encodes a P-type ATPase, CadA, that confers resistance to Cd(II)/Pb(II)/Zn(II). Expression 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. The crystal structure of CadC shows two types of metal binding sites, termed Site 1 and Site 2, and the homodimer has two of each. Site 1 is the physiological inducer binding site. The two Site 2 metal binding sites are formed at the dimerization interface. Site 2 is not regulatory in CadC but is regulatory in the homologue SmtB. Here the role of each site was investigated by mutagenesis. Both sites bind either Cd(II) or Zn(II). However, Site 1 has higher affinity for Cd(II) over Zn(II), and Site 2 prefers Zn(II) over Cd(II). Site 2 is not required for either derepression or dimerization. The crystal structure of the wild type with bound Zn(II) and of a mutant lacking Site 2 was compared with the SmtB structure with and without bound Zn(II). We propose that an arginine residue allows for Zn(II) regulation in SmtB and, conversely, a glycine results in a lack of regulation by Zn(II) in CadC. We propose that a glycine residue was ancestral whether the repressor binds Zn(II) at a Site 2 like CadC or has no Site 2 like the paralogous ArsR and implies that acquisition of regulatory ability in SmtB was a more recent evolutionary event. Role of bound Zn(II) in the CadC Cd(II)/Pb(II)/Zn(II)-responsive repressor.,Kandegedara A, Thiyagarajan S, Kondapalli KC, Stemmler TL, Rosen BP J Biol Chem. 2009 May 29;284(22):14958-65. Epub 2009 Mar 13. PMID:19286656[6] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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