This domain is found at the N-terminal end of Ubiquinone biosynthesis protein COQ9 from humans and similar proteins predominantly from vertebrates. COQ9 is a lipid-binding protein involved in the biosynthesis of coenzyme Q, also named ubiquinone, an essential lipid-soluble electron transporter for aerobic cellular respiration. This protein has structural homology to the TFR family of bacterial transcriptional regulators. This domain contains an a helix-turn- helix (HTH) motif that largely lacks the positive charges required for DNA binding [1,2].

1: Mitochondrial COQ9 is a lipid-binding protein that associates with COQ7 to enable coenzyme Q biosynthesis. Lohman DC, Forouhar F, Beebe ET, Stefely MS, Minogue CE, Ulbrich A, Stefely JA, Sukumar S, Luna-Sanchez M, Jochem A, Lew S, Seetharaman J, Xiao R, Wang H, Westphall MS, Wrobel RL, Everett JK, Mitchell JC, Lopez LC, Coon JJ, Tong L, Pagliarini DJ; Proc Natl Acad Sci U S A. 2014;111:E4697-E4705. PMID:25339443

2: An Isoprene Lipid-Binding Protein Promotes Eukaryotic Coenzyme Q Biosynthesis. Lohman DC, Aydin D, Von Bank HC, Smith RW, Linke V, Weisenhorn E, McDevitt MT, Hutchins P, Wilkerson EM, Wancewicz B, Russell J, Stefely MS, Beebe ET, Jochem A, Coon JJ, Bingman CA, Dal Peraro M, Pagliarini DJ; Mol Cell. 2019;73:763-774. PMID:30661980