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Koetter JW, Schulz GE: Crystal structure of 6-hydroxy-D-nicotine oxidase from Arthrobacter nicotinovorans. J Mol Biol. 2005 Sep 16;352(2):418-28.
The crystal structure of 6-hydroxy-d-nicotine oxidase (EC 1.5.3.6) was solved by X-ray diffraction analysis in three crystal forms at resolutions up to 1.9 A. The enzyme is monomeric in solution and also in the mother liquor but formed disulfide-dimers in all crystals. It belongs to the p-cresol methylhydroxylase-vanillyl-alcohol oxidase family and contains an FAD covalently bound to the polypeptide. The covalent bond of this enzyme was the first for which a purely autocatalytic formation had been shown. In contrast to previous reports, the bond does not involve N (epsilon2) (N3) of His72 but the N (delta1) (N1) atom. The geometry of this reaction is proposed and the autoflavinylation is discussed in the light of homologous structures. The enzyme is specific for 6-hydroxy-D-nicotine and is inhibited by the L-enantiomer. This observation was verified by modeling enzyme-substrate and enzyme-inhibitor complexes, which also showed the geometry of the catalyzed reaction. The binding models indicated that the deprotonation of the substrate rather than the hydride transfer is the specificity-determining step. The functionally closely related 6-hydroxy-L-nicotine oxidase processing the L-enantiomer is sequence-related to the greater glutathione reductase family with quite a different chainfold. A model of this "sister enzyme" derived from known homologous structures suggests that the reported L-substrate specificity and D-enantiomer inhibition are also determined by the location of the deprotonating base. |
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