The FAD-binding domain comprises regions E4-A152, K205-W319, and K499-K561 (Figure ) and presents a conserved fold previously observed in KstD1. The main part of the FADbinding domain adopts the super-secondary structure, the characteristic of the Rossmann fold (Figure ). Its arrangement differs from a basic topology and it is a typical variation of the fold noticed for dehydrogenases . The fold that binds dinucleotides such as FAD involves two Rossmann binding motifs, which typically form a six-stranded parallel β-sheet flanked by α- The FAD molecule is stabilized at the active site by a network of hydrogen bonds formed by residues: E37, K38, T45, S46, G50, A52, F233, N299, D302, N526, T542, and L543, as shown in Figure . Analysis of AcmB-FAD interactions also reveals numerous interactions of the π-alkyl (V13, K38, I496, F338), π-sigma (A270, L543), and alkyl-alkyl (A294, I496).