title: Structure of the prolyl-acyl carrier protein oxidase involved in the biosynthesis of the cyanotoxin anatoxin-a.
abstract: Anatoxin-a and homoanatoxin-a are two potent cyanobacterial neurotoxins biosynthesized from L-proline by a short pathway involving polyketide synthases. Proline is first loaded onto AnaD, an acyl carrier protein, and prolyl-AnaD is then oxidized to 1-pyrroline-5-carboxyl-AnaD by a flavoprotein, AnaB. Three polyketide synthases then transform this imine into anatoxin-a or homoanatoxin-a. AnaB was crystallized in its holo form and its three-dimensional structure was determined by X-ray diffraction at 2.8 Å resolution. AnaB is a homotetramer and its fold is very similar to that of the acyl-CoA dehydrogenases (ACADs). The active-site base of AnaB, Glu244, superimposed very well with that of human isovaleryl-CoA dehydrogenase, confirming previous site-directed mutagenesis experiments and mechanistic proposals. The substrate-binding site of AnaB is small and is likely to be fitted for the pyrrolidine ring of proline. However, in contrast to ACADs, which use an electron-transport protein, AnaB uses molecular oxygen as the electron acceptor, as in acyl-CoA oxidases. Calculation of the solvent-accessible surface area around the FAD in AnaB and in several homologues showed that it is significantly larger in AnaB than in its homologues. A protonated histidine near the FAD in AnaB is likely to participate in oxygen activation. Furthermore, an array of water molecules detected in the AnaB structure suggests a possible path for molecular oxygen towards FAD. This is consistent with AnaB being an oxidase rather than a dehydrogenase. The structure of AnaB is the first to be described for a prolyl-ACP oxidase and it will contribute to defining the structural basis responsible for oxygen reactivity in flavoenzymes.
authors: CNRS, UMR 7099, Institut de Biologie Physico-Chimique, 13 Rue Pierre et Marie Curie, 75005 Paris, France.
authors: Karine
authors: K
authors: Moncoq
authors: Leslie
authors: L
authors: Regad
authors: Stéphane
authors: S
authors: Mann
authors: Annick
authors: A
authors: Méjean
authors: Olivier
authors: O
authors: Ploux
mesh_terms: D000213:Acyl Carrier Protein / Q000737:chemistry* / Q000378:metabolism; D044944:Acyl-CoA Dehydrogenases / Q000737:chemistry / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001427:Bacterial Toxins / Q000378:metabolism*; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000378:metabolism*; D018360:Crystallography, X-Ray; D000458:Cyanobacteria / Q000737:chemistry / Q000201:enzymology* / Q000378:metabolism; D000087522:Cyanobacteria Toxins; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism; D016415:Sequence Alignment; D014326:Tropanes / Q000378:metabolism*
chemical_list: D000213:Acyl Carrier Protein; D001427:Bacterial Toxins; D019086:Bridged Bicyclo Compounds, Heterocyclic; D000087522:Cyanobacteria Toxins; D014326:Tropanes; C524097:homoanatoxin-a; C509783:anatoxin a; D010088:Oxidoreductases; D044944:Acyl-CoA Dehydrogenases
keywords: acyl-CoA dehydrogenase; acyl-CoA oxidase; anatoxin-a; flavin; homoanatoxin-a; proline