Fig. 4.

Probable quaternary dimers of PixD as based on the PixD crystal structure. The flavin molecules are represented in a stick–sphere model. Within the same asymmetry unit, the PixD dimers could be either between subunits from separate rings indicated as [AB] or between subunits within the same ring indicated as [AC]. The interfacing residues are colored red for [AC] type dimers or blue for [AB] type dimers. [AB]-interfacing residues include: I78, Y63, N60, C80, Y4, and Q68 for subunit A and Y4, H64, Q76, I77, I78, and C80 for subunit B. [AC]-interfacing residues include: I111, K112, Y113, S114, K120, D125, E127, and Q128 for subunit A and E55, I83, K84, K85, K86, and K84 for subunit C.