Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 102, Issue 51, Pages 18408-18413Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.0500908102
Keywords
iron; homeostasis; transcription regulation
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Funding
- NCRR NIH HHS [P41 RR010888, P41-RR10888, S10-RR10493] Funding Source: Medline
- NIAID NIH HHS [R01 AI021628, AI21628] Funding Source: Medline
- NIGMS NIH HHS [GM68762, P50 GM068762] Funding Source: Medline
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The diphtheria toxin repressor (DtxR) is a metal ion-activated transcriptional regulator that has been linked to the virulence of Corynebacterium diphtheriae. Structure determination has shown that there are two metal ion binding sites per repressor monomer, and site-directed mutagenesis has demonstrated that binding site 2 (primary) is essential for recognition of the target DNA repressor, leaving the role of binding site 1 (ancillary) unclear. Calorimetric techniques have demonstrated that although binding site 1 (ancillary) has high affinity for metal ion with a binding constant of 2 x 10(-7), binding site 2 (primary) is a low-affinity binding site with a binding constant of 6.3 x 10(-4). These two binding sites act in an independent fashion, and their contribution can be easily dissected by traditional mutational analysis. Our results clearly demonstrate that binding site 1 (ancillary) is the first one to be occupied during metal ion activation, playing a critical role in stabilization of the repressor. In addition, structural data obtained for the mutants Ni-DtxR(H79A,C102D), reported here, and the previously reported DtxR(H79A) have allowed us to propose a mechanism of metal activation for DtxR.
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