This is a DNA-binding, winged helix-turn-helix (wHTH) domain of about 65 amino acids present in metalloregulators of the dtxR/mntR family.

Iron-responsive metalloregulators such as dtxR and ideR occur in Gram-positive bacteria of the high GC branch, while manganese-responsive metalloregulators like mntR are described in diverse genera of Gram-positive and Gram-negative bacteria and also in Archaea.

The dtxR protein regulates the expression of diphtheria toxin in response to environmental iron concentrations.

The crystal structures of iron-regulated and manganese-regulated repressors show that the DNA binding domain contains three alpha-helices and a pair of antiparallel beta-strands.

Metal-bound dtxR represses transcription by binding the tox operator; if iron is limiting, conformational changes of the wHTH disrupt DNA-binding and the diphtheria toxin is produced.