FIGURE 6.

Hydrogen bonding in electron-bifurcating FADs. Arginine and lysine residues that form hydrogen bonds with FAD are red; in FAD, green, blue, orange, and yellow indicate carbon, nitrogen, oxygen, and phosphorus, respectively; the hydrogen bonds of FAD are shown as yellow dotted lines. (A) N₅ of b-FAD binds an arginine residue (Arg¹⁸⁷ of T. maritima NfnB, PDB: 4YRY). (B) N₅ of FAD binds an arginine residue (Arg¹⁴⁶ of A. fermentans EftA, PDB: 4KPU). (C) N₅ of FAD binds a lysine residue (Lys⁴⁰⁹ of Methanothermococcus thermolithotrophicus HdrA, PDB: 5ODC).