duplication of the core domain accompanied by segment-swapping; the N-terminal domain has an interrupted canonical fold and binds FAD, whereas the C-terminal domain has a circularly permuted fold (SCOP ID 2000034) and, in some members, binds NAD(P)
the characteristic meander beta-sheet, connecting strands 3 and 4 of the main beta-sheet, is replaced with alpha-helix in the N-terminal domain, but remains in the C-terminal domain