Comparison of high-resolution structures of the diphtheria toxin repressor in complex with cobalt and zinc at the cation-anion binding site.
The diphtheria toxin repressor (DtxR) from Corynebacterium diphtheriae is a divalent-metal activated repressor of chromosomal genes responsible for siderophore-mediated iron-uptake and of a gene on several corynebacteriophages that encodes diphtheria toxin. Even though DtxR is the best characterized iron-dependent repressor to date, numerous key properties of the protein still remain to be explained. One is the role of the cation-anion pair discovered in its first metal-binding site. A second is the reason why zinc exhibits its activating effect only at a concentration 100-fold higher than other divalent cations. In the presently reported 1.85 A resolution Co-DtxR structure at 100K, the sulfate anion in the cation-anion-binding site interacts with three side chains that are all conserved in the entire DtxR family, which points to a possible physiological role of the anion. A comparison of the 1.85 A Cobalt-DtxR structure at 100K and the 2.4 A Zinc-DtxR structure at room temperature revealed no significant differences. Hence, the difference in efficiency of Co2+ and Zn2+ to activate DtxR remains a mystery and might be hidden in the properties of the intriguing second metal-binding site. Our studies do, however, provide a high resolution view of the cationanion-binding site that has most likely evolved to interact not only with a cation but also with the anion in a very precise manner.
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Department of Biological Structure, University of Washington, Seattle 98195-7742, USA.
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D001426:Bacterial Proteins / Q000737:chemistry* / Q000378:metabolism*; D001665:Binding Sites; D002413:Cations, Divalent / Q000378:metabolism; D003035:Cobalt / Q000378:metabolism*; D003353:Corynebacterium diphtheriae; D018360:Crystallography, X-Ray; D004268:DNA-Binding Proteins / Q000737:chemistry* / Q000378:metabolism*; D006860:Hydrogen Bonding; D008958:Models, Molecular; D017433:Protein Structure, Secondary; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D012984:Software; D015032:Zinc / Q000378:metabolism*
D001426:Bacterial Proteins; D002413:Cations, Divalent; D004268:DNA-Binding Proteins; C075586:DtxR protein, Corynebacterium diphtheriae; D011994:Recombinant Proteins; D003035:Cobalt; D015032:Zinc