title: Plant carotene cis-trans isomerase CRTISO: a new member of the FAD(RED)-dependent flavoproteins catalyzing non-redox reactions.
abstract: The carotene cis-trans isomerase CRTISO is a constituent of the carotene desaturation pathway as evolved in cyanobacteria and prevailing in plants, in which a tetra-cis-lycopene species, termed prolycopene, is formed. CRTISO, an evolutionary descendant of the bacterial carotene desaturase CRTI, catalyzes the cis-to-trans isomerization reactions leading to all-trans-lycopene, the substrate for the subsequent lycopene cyclization to form all-trans-α/β-carotene. CRTISO and CRTI share a dinucleotide binding motif at the N terminus. Here we report that this site is occupied by FAD in CRTISO. The reduced form of this cofactor catalyzes a reaction not involving net redox changes. Results obtained with C(1)- and C(5)-deaza-FAD suggest mechanistic similarities with type II isopentenyl diphosphate: dimethylallyl diphosphate isomerase (IDI-2). CRTISO, together with lycopene cyclase CRTY and IDI-2, thus represents the third enzyme in isoprenoid metabolism belonging to the class of non-redox enzymes depending on reduced flavin for activity. The regional specificity and the kinetics of the isomerization reaction were investigated in vitro using purified enzyme and biphasic liposome-based systems carrying specific cis-configured lycopene species as substrates. The reaction proceeded from cis to trans, recognizing half-sides of the symmetrical prolycopene and was accompanied by one trans-to-cis isomerization step specific for the C(5)-C(6) double bond. Rice lycopene β-cyclase (OsLCY-b), when additionally introduced into the biphasic in vitro system used, was found to be stereospecific for all-trans-lycopene and allowed the CRTISO reaction to proceed toward completion by modifying the thermodynamics of the overall reaction.
authors.affiliation: From the Faculty of Biology, Centre for Biological Signaling Studies (Bioss), University of Freiburg, D-79104 Freiburg, Germany.
authors.forename: Qiuju
authors.initials: Q
authors.lastname: Yu
authors.affiliation: the Department of Biology, University of Konstanz, D-78457 Konstanz, Germany and.
authors.forename: Sandro
authors.initials: S
authors.lastname: Ghisla
authors.affiliation: the Department of Genetics, the Alexander Silberman Life Science Institute, Hebrew University of Jerusalem, 91904 Jerusalem, Israel.
authors.forename: Joseph
authors.initials: J
authors.lastname: Hirschberg
authors.affiliation: the Department of Genetics, the Alexander Silberman Life Science Institute, Hebrew University of Jerusalem, 91904 Jerusalem, Israel.
authors.forename: Varda
authors.initials: V
authors.lastname: Mann
authors.affiliation: From the Faculty of Biology, Centre for Biological Signaling Studies (Bioss), University of Freiburg, D-79104 Freiburg, Germany,. Electronic address: peter.beyer@biologie.uni-freiburg.de.
authors.forename: Peter
authors.initials: P
authors.lastname: Beyer
mesh_terms: D020816:Amino Acid Motifs; D002338:Carotenoids / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005182:Flavin-Adenine Dinucleotide / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D005420:Flavoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018551:Solanum lycopersicum / Q000201:enzymology* / Q000235:genetics; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D019745:cis-trans-Isomerases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D005420:Flavoproteins; D010940:Plant Proteins; D005182:Flavin-Adenine Dinucleotide; D002338:Carotenoids; D019745:cis-trans-Isomerases