Structural Elements of Metal Selectivity in Metal Sensor Proteins

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 100; no. 7; pp. 3713 - 3718
• Main Authors: Pennella, Mario A., Shokes, Jacob E., Cosper, Nathaniel J., Scott, Robert A., Giedroc, David P.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 01.04.2003; National Acad Sciences; The National Academy of Sciences
• Series: Bioinorganic Chemistry Special Feature
• Subjects: Allosteric regulation; Amino Acid Sequence; Bacterial Proteins - chemistry; Bacterial Proteins - metabolism; Bioinorganic Chemistry Special Feature; Cobalt - metabolism; Coordination polymers; Cyanobacteria - genetics; CzrA protein; Dimers; DNA; DNA-Binding Proteins - chemistry; DNA-Binding Proteins - metabolism; Gene expression regulation; Ligands; Metal ions; Metals; Metals - metabolism; Molecular Sequence Data; Monomers; Mycobacterium tuberculosis; Nickel - metabolism; NmtR protein; Physical Sciences; Proteins; Recombinant Proteins - chemistry; Recombinant Proteins - metabolism; Sensors; Sequence Alignment; Sequence Homology, Amino Acid; Spectrophotometry; Spectrophotometry, Atomic; Staphylococcus aureus; Staphylococcus aureus - chemistry; Ultracentrifugation; Zinc - metabolism
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0636943100

Staphylococcus aureus CzrA and Mycobacterium tuberculosis NmtR are homologous zinc/cobalt-responsive and nickel/cobalt-responsive transcriptional repressors in vivo, respectively, and members of the ArsR/SmtB superfamily of prokaryotic metal sensor proteins. We show here that Zn(II) is the most potent negative allosteric regulator of czr operator/promoter binding in vitro with the trend Zn(II)>Co(II)≫Ni(II), whereas the opposite holds for the binding of NmtR to the nmt operator/promoter, Ni(II)>Co(II)>Zn(II). Characterization of the metal coordination complexes of CzrA and NmtR by UV/visible and x-ray absorption spectroscopies reveals that metals that form four-coordinate tetrahedral complexes with CzrA [Zn(II) and Co(II)] are potent regulators of DNA binding, whereas metals that form five- or six-coordinate complexes with NmtR [Ni(II) and Co(II)] are the strongest allosteric regulators in this system. Strikingly, the Zn(II) coordination complexes of CzrA and NmtR cannot be distinguished from one another by x-ray absorption spectroscopy, with the best fit a His-3-carboxylate complex in both cases. Inspection of the primary structures of CzrA and NmtR, coupled with previous functional data, suggests that three conserved His and one Asp from the C-terminal α5 helix donate ligands to create a four-coordinate complex in both CzrA and NmtR, with NmtR uniquely capable of expanding its coordination number in the Ni(II) and Co(II) complexes by recruiting additional His ligands from a C-terminal extension of the α5 helix.