Members of this family adopt an alpha+beta sandwich structure with an antiparallel beta-sheet, in a ferredoxin-like fold. They are predominantly found in plant cytokinin dehydrogenase 1, where they are capable of binding both FAD and cytokinin substrates. The substrate displays a 'plug-into-socket' binding mode that seals the catalytic site and precisely positions the carbon atom undergoing oxidation in close contact with the reactive locus of the flavin [1].

1: Structures of Michaelis and product complexes of plant cytokinin dehydrogenase: implications for flavoenzyme catalysis. Malito E, Coda A, Bilyeu KD, Fraaije MW, Mattevi A; J Mol Biol. 2004;341:1237-1249. PMID:15321719