InterPro domain: IPR016164

This superfamily represents a structural domain found at the C-terminal of several FAD-linked oxidases. This domain consists of two structural subdomains: subdomain 1 is a 2-layer a/b or 3-layer a/b/a sandwich, and subdomain 2 is either an orthogonal alpha-bundle or a second 2-layer a/b sandwich. It can be found in the following proteins:

• Vanillyl-alcohol family, which includes the flavoprotein vanillyl-alcohol oxidase ( 1.1.3.38 ) [ 1 ] as well as the flavoprotein subunit of p-cresol methylhydroxylase ( 1.17.99.1 ) (the other subunit being a short chain cytochrome c) [ 2 ], both of these enzymes contain covalently bound FAD.
• D-lactate dehydrogenases ( 1.1.1.28 , 1.1.2.4 -cytochrome), a peripheral membrane respiratory enzyme involved in electron transfer for the energization of active transport of a variety of sugars and amino acids in bacteria [ 3 ].
• Cholesterol oxidases ( 1.1.3.6 ), a monomeric flavoenzyme that catalyses the oxidation and isomerisation of cholesterol to cholest-4-en-3-one [ 4 ].
• Cytokinin dehydrogenase 1 ( 1.5.99.12 ), which has a major role in the control of plant cytokinin hormone levels by catalysing their irreversible oxidation [ 5 ].

1. Covalent flavinylation is essential for efficient redox catalysis in vanillyl-alcohol oxidase. J. Biol. Chem. 274, 35514-20
2. p-Cresol methylhydroxylase: alteration of the structure of the flavoprotein subunit upon its binding to the cytochrome subunit. Biochemistry 44, 2963-73
3. The crystal structure of D-lactate dehydrogenase, a peripheral membrane respiratory enzyme. Proc. Natl. Acad. Sci. U.S.A. 97, 9413-8
4. Oxygen access to the active site of cholesterol oxidase through a narrow channel is gated by an Arg-Glu pair. J. Biol. Chem. 276, 30435-41
5. Structures of Michaelis and product complexes of plant cytokinin dehydrogenase: implications for flavoenzyme catalysis. J. Mol. Biol. 341, 1237-49