title: The lycopene cyclase CrtY from Pantoea ananatis (formerly Erwinia uredovora) catalyzes an FADred-dependent non-redox reaction.
abstract: The cyclization of lycopene generates provitamin A carotenoids such as beta-carotene and paves the way toward the formation of cyclic xanthophylls playing distinct roles in photosynthesis and as precursors for regulatory molecules in plants and animals. The biochemistry of lycopene cyclization has been enigmatic, as the previously proposed acid-base catalysis conflicted with the possibility of redox catalysis as predicted by the presence of a dinucleotide binding site. We show that reduced FAD is the essential lycopene cyclase (CrtY) cofactor. Using flavin analogs, mass spectrometry, and mutagenesis, evidence was obtained based on which a catalytic mechanism relying on cryptic (net) electron transfer can be refuted. The role of reduced FAD is proposed to reside in the stabilization of a transition state carrying a (partial) positive charge or of a positively charged intermediate via a charge transfer interaction, acid-base catalysis serving as the underlying catalytic principle. Lycopene cyclase, thus, ranks among the novel class of non-redox flavoproteins, such as isopentenyl diphosphate:dimethylallyl diphosphate isomerase type 2 (IDI-2) that requires the reduced form of the cofactor.
authors.affiliation: Faculty of Biology, University of Freiburg, D-79104 Freiburg, Germany.
authors.forename: Qiuju
authors.initials: Q
authors.lastname: Yu
authors.forename: Patrick
authors.initials: P
authors.lastname: Schaub
authors.forename: Sandro
authors.initials: S
authors.lastname: Ghisla
authors.forename: Salim
authors.initials: S
authors.lastname: Al-Babili
authors.forename: Anja
authors.initials: A
authors.lastname: Krieger-Liszkay
authors.forename: Peter
authors.initials: P
authors.lastname: Beyer
mesh_terms: D019943:Amino Acid Substitution; D001059:Apoproteins / Q000235:genetics / Q000378:metabolism; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D002338:Carotenoids / Q000096:biosynthesis / Q000737:chemistry; D002384:Catalysis; D003067:Coenzymes / Q000737:chemistry / Q000378:metabolism; D017931:DNA Primers / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D004926:Escherichia coli / Q000201:enzymology / Q000235:genetics; D005182:Flavin-Adenine Dinucleotide / Q000031:analogs & derivatives / Q000737:chemistry / Q000378:metabolism; D019753:Intramolecular Lyases / Q000235:genetics / Q000378:metabolism*; D007700:Kinetics; D000077276:Lycopene; D008566:Membranes / Q000201:enzymology; D015394:Molecular Structure; D016297:Mutagenesis, Site-Directed; D010084:Oxidation-Reduction; D020636:Pantoea / Q000201:enzymology* / Q000235:genetics; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D001059:Apoproteins; D001426:Bacterial Proteins; D003067:Coenzymes; D017931:DNA Primers; D004269:DNA, Bacterial; D011994:Recombinant Proteins; D005182:Flavin-Adenine Dinucleotide; D002338:Carotenoids; D019753:Intramolecular Lyases; C070925:lycopene cyclase-isomerase; D000077276:Lycopene