Fig. 4: Structural analyses of the active site of VibO.

a The combined surface representation and the stick-ball model showing the substrate-binding pocket docked with substrate 6 as well as the proposed substrate entrance or product leaving channel of VibO. b The ribbon-stick-ball representation showing the detailed interactions of substrate 6 (Sub 6) with the active site residues within the substrate-binding pocket of VibO in the structure model of VibO docked with substrate 6 by Autodock Vina program. The relevant hydrogen bonds involved in the interaction of substrate 6 with VibO in the complex model are shown as dotted black lines, and the distance between the carbon C6 of substrate 6 and the C4a atom of the bound FAD of VibO is further indicated and shown as a dotted green line. c The ribbon-stick-ball representation showing the detailed comparison of the proposed key R52 and R225 residues of the type-O BVMO MtmOIV for stabilizing the negatively charged flavin-OO^‒ intermediate with the corresponding residues of VibO. d The ribbon-stick-ball representation showing the detailed comparison of the proposed key residues of the group A FMO PHHY for stabilizing the flavin-OOH intermediate with the corresponding residues of VibO. These structural analyses reveal that VibO contains essential structural elements for stabilizing both types of flavin co-factors (flavin-OO^‒ and flavin-OOH).