This domain is found at the N-terminus of the TruD protein [1] a protein involved in cyanobactin heterocyclisation. It adopts a winged helix-turn-helix structure. It is also found in the related LynD protein [2].

1: The cyanobactin heterocyclase enzyme: a processive adenylase that operates with a defined order of reaction. Koehnke J, Bent AF, Zollman D, Smith K, Houssen WE, Zhu X, Mann G, Lebl T, Scharff R, Shirran S, Botting CH, Jaspars M, Schwarz-Linek U, Naismith JH; Angew Chem Int Ed Engl. 2013;52:13991-13996. PMID:24214017

2: Structural analysis of leader peptide binding enables leader-free cyanobactin processing. Koehnke J, Mann G, Bent AF, Ludewig H, Shirran S, Botting C, Lebl T, Houssen W, Jaspars M, Naismith JH; Nat Chem Biol. 2015;11:558-563. PMID:26098679