The bacterial iron sensor IdeR recognizes its DNA targets by indirect readout

ABSTRACTIdeR is the main transcriptional regulator controlling iron homeostasis genes in Actinobacteria, including species from the Corynebacterium, Mycobacterium, and Streptomyces genera, as well as the erythromycin-producing bacterium Saccharopolyspora erythraea. Despite being a well-studied transcription factor since the identification of the Diphtheria toxin repressor DtxR three decades ago, the details of how IdeR proteins recognize their highly conserved 19-bp DNA target remain to be elucidated. The results of our structural and mutational studies support a model wherein IdeR uses an indirect readout mechanism, identifying its targets via the sequence-specific DNA backbone structure rather than through direct contacts with the DNA bases. Furthermore, we show that IdeR efficiently recognizes a shorter palindromic sequence corresponding to a half binding site as compared to the full 19-bp target previously reported, expanding the number of potential target genes controlled by IdeR proteins.

Crystallization and preliminary X-ray diffraction analysis of the metalloregulatory protein DtxR fromThermoplasma acidophilum

The diphtheria toxin repressor (DtxR) is a metal-ion-dependent transcriptional regulator which regulates genes encoding proteins involved in metal-ion uptake to maintain metal-ion homeostasis. DtxR fromThermoplasma acidophilumwas cloned and overexpressed inEscherichia coli. Crystals of N-terminally His-tagged DtxR were obtained by hanging-drop vapour diffusion and diffracted to 1.8 Å resolution. DtxR was crystallized at 296 K using polyethylene glycol 4000 as a precipitant. The crystals belonged to the orthorhombic space groupP21212, with unit-cell parametersa= 61.14,b= 84.61,c= 46.91 Å, α = β = γ = 90°. The asymmetric unit contained approximately one monomer of DtxR, giving a crystal volume per mass (VM) of 2.22 Å3 Da−1and a solvent content of 44.6%.