title: Hydroxylation and ring-opening mechanism of an unusual flavoprotein monooxygenase, 2-methyl-3-hydroxypyridine-5-carboxylic acid oxygenase: a theoretical study.
abstract: Hybrid meta-GGA density functional theory (the MPWB1K functional) was used to study the hydroxylation and ring-opening mechanism of 2-methyl-3-hydroxypyridine-5-carboxylic acid oxygenase (MHPCO). This enzyme catalyses the conversion of 2-methyl-3-hydroxypyridine-5-carboxylic acid (MHPC) to alpha-(N-acetylaminomethylene)succinic acid (AAMS), which is the essential ring-opening step in the bacterial degradation of vitamin B(6). MHPCO belongs to the flavin-containing aromatic hydroxylases family. However, MHPCO is capable of catalysing a subsequent aromatic ring-cleavage reaction to give acyclic products rather than hydroxylated aromatic ones. Our calculations show that the re-aromatisation of the hydroxylated intermediate occurs spontaneously in aqueous solution; this implies that the ring-opening process occurs inside the enzyme's active site, in which limited water is available. The instability of the hydroxylated intermediate of MHPCO is the main reason why acyclic products are formed. Previously proposed mechanisms for the ring-opening step were studied, and were shown to be less likely to occur (DeltaDeltaG(not equal298)>35 kcal mol(-1)). Two new pathways with reasonable barrier heights (DeltaDeltaG(not equal 298)<15 kcal mol(-1)) are reported herein, which are in accordance with all experimental information present to date.
authors.affiliation: Orebro Life Science Center School of Science and Technology, Orebro University, 70182 Orebro, Sweden.
authors.forename: Boxue
authors.initials: B
authors.lastname: Tian
authors.forename: Yaoquan
authors.initials: Y
authors.lastname: Tu
authors.forename: Ake
authors.initials: A
authors.lastname: Strid
authors.forename: Leif A
authors.initials: LA
authors.lastname: Eriksson
mesh_terms: D001665:Binding Sites; D002384:Catalysis; D005420:Flavoproteins / Q000737:chemistry*; D006900:Hydroxylation; D008958:Models, Molecular; D008962:Models, Theoretical; D009539:Nicotinic Acids / Q000737:chemistry*; D010105:Oxygenases / Q000737:chemistry*; D014815:Vitamins / Q000737:chemistry
chemical_list: C106693:2-methyl-3-hydroxypyridine-5-carboxylic acid; D005420:Flavoproteins; D009539:Nicotinic Acids; D014815:Vitamins; D010105:Oxygenases