Modelling of a neisserial OxyR tetramer. The OxyR regulatory domain shown in grey was superimposed onto the tetrameric structures of (a) CbnR (PDB code 1IZ1). (b) PA01 (PDB id 3FZV) and (c) PA0477 (PDB id 2ESN). The α3 and α4 helices which flank the C199 and C208 residues (shown as solid spheres) are coloured orange. The two pairs of dimers which form each tetramer are coloured bright/light blue (A:C in PA01 and PA0477; A:Q in CbnR) and bright/light cyan (B:D in PA01 and PA0477; B:P in CbnR).