title: Role of bound Zn(II) in the CadC Cd(II)/Pb(II)/Zn(II)-responsive repressor.
abstract: The 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.
authors.affiliation: Department of Biochemistry and Molecular Biology, Wayne State University, School of Medicine, Detroit, Michigan 48201, USA.
authors.forename: Ashoka
authors.initials: A
authors.lastname: Kandegedara
authors.forename: Saravanamuthu
authors.initials: S
authors.lastname: Thiyagarajan
authors.forename: Kalyan C
authors.initials: KC
authors.lastname: Kondapalli
authors.forename: Timothy L
authors.initials: TL
authors.lastname: Stemmler
authors.forename: Barry P
authors.initials: BP
authors.lastname: Rosen
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D001665:Binding Sites; D002104:Cadmium / Q000378:metabolism; D018360:Crystallography, X-Ray; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D007854:Lead / Q000378:metabolism; D013058:Mass Spectrometry; D019216:Metals, Heavy / Q000378:metabolism*; D050505:Mutant Proteins / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D055503:Protein Multimerization; D017433:Protein Structure, Secondary; D012097:Repressor Proteins / Q000737:chemistry / Q000378:metabolism*; D013211:Staphylococcus aureus / Q000378:metabolism*; D015032:Zinc / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; C080050:CadC protein, Bacteria; D004268:DNA-Binding Proteins; D019216:Metals, Heavy; D050505:Mutant Proteins; D012097:Repressor Proteins; D002104:Cadmium; D007854:Lead; D015032:Zinc