title: Aminoacetone oxidase from Streptococcus oligofermentans belongs to a new three-domain family of bacterial flavoproteins.
abstract: The aaoSo gene from Streptococcus oligofermentans encodes a 43 kDa flavoprotein, aminoacetone oxidase (SoAAO), which was reported to possess a low catalytic activity against several different L-amino acids; accordingly, it was classified as an L-amino acid oxidase. Subsequently, SoAAO was demonstrated to oxidize aminoacetone (a pro-oxidant metabolite), with an activity ~25-fold higher than the activity displayed on L-lysine, thus lending support to the assumption of aminoacetone as the preferred substrate. In the present study, we have characterized the SoAAO structure-function relationship. SoAAO is an FAD-containing enzyme that does not possess the classical properties of the oxidase/dehydrogenase class of flavoproteins (i.e. no flavin semiquinone formation is observed during anaerobic photoreduction as well as no reaction with sulfite) and does not show a true L-amino acid oxidase activity. From a structural point of view, SoAAO belongs to a novel protein family composed of three domains: an α/β domain corresponding to the FAD-binding domain, a β-domain partially modulating accessibility to the coenzyme, and an additional α-domain. Analysis of the reaction products of SoAAO on aminoacetone showed 2,5-dimethylpyrazine as the main product; we propose that condensation of two aminoacetone molecules yields 3,6-dimethyl-2,5-dihydropyrazine that is subsequently oxidized to 2,5-dimethylpyrazine. The ability of SoAAO to bind two molecules of the substrate analogue O-methylglycine ligand is thought to facilitate the condensation reaction. A specialized role for SoAAO in the microbial defence mechanism related to aminoacetone catabolism through a pathway yielding dimethylpyrazine derivatives instead of methylglyoxal can be proposed.
authors.affiliation: *Dipartimento di Biotecnologie e Scienze della Vita, Università degli Studi deII'Insubria, via J.H. Dunant 3, 21100 Varese, ltaly.
authors.forename: Gianluca
authors.initials: G
authors.lastname: Molla
authors.affiliation: ‡Dipartimento di Bioscienze, Università degli Studi di Milano, 20133 Milano, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Nardini
authors.affiliation: *Dipartimento di Biotecnologie e Scienze della Vita, Università degli Studi deII'Insubria, via J.H. Dunant 3, 21100 Varese, ltaly.
authors.forename: Paolo
authors.initials: P
authors.lastname: Motta
authors.affiliation: †The Protein Factory, Centro Interuniversitario di Biotecnologie Proteiche, Politecnico di Milano, ICRM CNR Milano, and Università degli Studi deII'Insubria, Varese, Italy.
authors.forename: Paola
authors.initials: P
authors.lastname: D'Arrigo
authors.affiliation: ║CNR-Istituto di Chimica del Riconoscimento Molecolare, Politecnico di Milano, via Mancinelli 7, 20131 Milano, Italy.
authors.forename: Walter
authors.initials: W
authors.lastname: Panzeri
authors.affiliation: *Dipartimento di Biotecnologie e Scienze della Vita, Università degli Studi deII'Insubria, via J.H. Dunant 3, 21100 Varese, ltaly.
authors.forename: Loredano
authors.initials: L
authors.lastname: Pollegioni
mesh_terms: D000096:Acetone / Q000031:analogs & derivatives / Q000378:metabolism; D018360:Crystallography, X-Ray; D004789:Enzyme Activation; D005420:Flavoproteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D005998:Glycine / Q000031:analogs & derivatives / Q000378:metabolism; D008958:Models, Molecular; D005810:Multigene Family; D000587:Oxidoreductases Acting on CH-NH Group Donors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D017434:Protein Structure, Tertiary; D011719:Pyrazines / Q000378:metabolism; D013291:Streptococcus / Q000201:enzymology* / Q000235:genetics / Q000378:metabolism; D000097667:Polyamine Oxidase
chemical_list: D000096:Acetone; D005420:Flavoproteins; D005998:Glycine; D000587:Oxidoreductases Acting on CH-NH Group Donors; D011719:Pyrazines; D000097667:Polyamine Oxidase; C035591:glycine methyl ester; C075524:2,5-dimethylpyrazine; C006495:aminoacetone