The Soft Metal Ion Binding Sites in theStaphylococcus aureuspI258 CadC Cd(II)/Pb(II)/Zn(II)-responsive Repressor Are Formed between Subunits of the Homodimer

Marco D. Wong, Yung-Feng Lin, Barry P. Rosen
2002 Journal of Biological Chemistry  
The Staphylococcus aureus plasmid pI258 CadC is a homodimeric repressor that binds Cd(II), Pb(II), and Zn(II) and regulates expression of the cadAC operon. CadC binds two Cd(II) ions per dimer, with a tetrathiolate binding site composed of residues Cys 7 , Cys 11 , Cys 58 , and Cys 60 . It is not known whether each site consists of residues from a single monomer or from residues contributed by both subunits. To examine whether Cys 7 and Cys 11 are spatially proximate to Cys 58 and Cys 60 of the
more » ... same subunit or of the other subunit, homodimers with the same cysteine mutation in each subunit and heterodimers containing different cysteine mutations in the two subunits were reacted with 4,6-bis(bromomethyl)-3,7-dimethyl-1,5-diazabicyclo[3.3.0]octa-3,6diene-2,8-dione, which cross-links thiol groups that are within 3-6 Å of each other. Cys 7 or Cys 11 cross-linked only with Cys 58 or Cys 60 on the other subunit. The data demonstrate that Cys 7 and Cys 11 from one monomer are within 3-6 Å of either Cys 58 or Cys 60 in the other monomer. The results of this study strongly indicate that each of the two Cd(II) binding sites in the CadC homodimer is composed of Cys 7 and Cys 11 from one monomer and Cys 58 and Cys 60 from the other monomer.
doi:10.1074/jbc.m206536200 pmid:12176999 fatcat:l5gyewly4navra6qtewn2l3dki