title: On the structure and function of the phytoene desaturase CRTI from Pantoea ananatis, a membrane-peripheral and FAD-dependent oxidase/isomerase.
abstract: CRTI-type phytoene desaturases prevailing in bacteria and fungi can form lycopene directly from phytoene while plants employ two distinct desaturases and two cis-tans isomerases for the same purpose. This property renders CRTI a valuable gene to engineer provitamin A-formation to help combat vitamin A malnutrition, such as with Golden Rice. To understand the biochemical processes involved, recombinant CRTI was produced and obtained in homogeneous form that shows high enzymatic activity with the lipophilic substrate phytoene contained in phosphatidyl-choline (PC) liposome membranes. The first crystal structure of apo-CRTI reveals that CRTI belongs to the flavoprotein superfamily comprising protoporphyrinogen IX oxidoreductase and monoamine oxidase. CRTI is a membrane-peripheral oxidoreductase which utilizes FAD as the sole redox-active cofactor. Oxygen, replaceable by quinones in its absence, is needed as the terminal electron acceptor. FAD, besides its catalytic role also displays a structural function by enabling the formation of enzymatically active CRTI membrane associates. Under anaerobic conditions the enzyme can act as a carotene cis-trans isomerase. In silico-docking experiments yielded information on substrate binding sites, potential catalytic residues and is in favor of single half-site recognition of the symmetrical C(40) hydrocarbon substrate.
authors: Faculty of Biology, Centre for Biological Signaling Studies, University of Freiburg, Freiburg, Germany.
authors: Patrick
authors: P
authors: Schaub
authors: Qiuju
authors: Q
authors: Yu
authors: Sandra
authors: S
authors: Gemmecker
authors: Pierre
authors: P
authors: Poussin-Courmontagne
authors: Justine
authors: J
authors: Mailliot
authors: Alastair G
authors: AG
authors: McEwen
authors: Sandro
authors: S
authors: Ghisla
authors: Salim
authors: S
authors: Al-Babili
authors: Jean
authors: J
authors: Cavarelli
authors: Peter
authors: P
authors: Beyer
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D002338:Carotenoids / Q000378:metabolism; D010088:Oxidoreductases / Q000737:chemistry* / Q000378:metabolism*; D020636:Pantoea / Q000201:enzymology*; D019745:cis-trans-Isomerases / Q000737:chemistry / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D002338:Carotenoids; C100185:(all-E) phytoene; D010088:Oxidoreductases; C022398:phytoene dehydrogenase; D019745:cis-trans-Isomerases