title: Chloroplast import of four carotenoid biosynthetic enzymes in vitro reveals differential fates prior to membrane binding and oligomeric assembly.
abstract: The precursor proteins of the carotenogenic enzymes geranylgeranyl diphosphate synthase, phytoene synthase, phytoene desaturase and lycopene cyclase were imported into isolated pea chloroplasts. Geranylgeranyl diphosphate synthase remained soluble in the stroma in a free form and phytoene synthase associated to thylakoid membranes upon import, both as expected. Surprisingly, phytoene desaturase and lycopene cyclase, which strongly depend on membrane association for enzymatic activity, also remained soluble in the chloroplast stroma. The soluble forms of these enzymes were, however, still competent for membrane-association, e.g. with protein-free liposomal membranes. Indeed the soluble forms of phytoene synthase, phytoene desaturase and lycopene cyclase occurred as ATP- and cold-sensitive high-molecular-mass complexes. Gel-filtration experiments and blue native-PAGE plus autoradiography and western blot analysis indicated a participation of the chloroplast 60-kDa chaperonin (Cpn60) in the soluble high-molecular-mass complexes of imported carotenogenic enzymes. Finally, it was inferred that a membrane-bound regulatory factor plays a decisive role in membrane-binding.
authors.affiliation: Institut für Biologie II, Zellbiologie, Universität Freiburg, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Bonk
authors.forename: B
authors.initials: B
authors.lastname: Hoffmann
authors.forename: J
authors.initials: J
authors.lastname: Von Lintig
authors.forename: M
authors.initials: M
authors.lastname: Schledz
authors.forename: S
authors.initials: S
authors.lastname: Al-Babili
authors.forename: E
authors.initials: E
authors.lastname: Hobeika
authors.forename: H
authors.initials: H
authors.lastname: Kleinig
authors.forename: P
authors.initials: P
authors.lastname: Beyer
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D019883:Alkyl and Aryl Transferases; D001692:Biological Transport; D002338:Carotenoids / Q000096:biosynthesis*; D018834:Chaperonin 60 / Q000378:metabolism; D002736:Chloroplasts / Q000201:enzymology / Q000378:metabolism*; D003001:Cloning, Molecular; D003080:Cold Temperature; D051231:Farnesyltranstransferase; D051232:Geranylgeranyl-Diphosphate Geranylgeranyltransferase; D019753:Intramolecular Lyases; D007535:Isomerases / Q000378:metabolism*; D008081:Liposomes; D008969:Molecular Sequence Data; D008970:Molecular Weight; D010088:Oxidoreductases / Q000378:metabolism*; D018532:Pisum sativum / Q000378:metabolism; D014166:Transferases / Q000378:metabolism*
chemical_list: D018834:Chaperonin 60; D008081:Liposomes; D002338:Carotenoids; D000255:Adenosine Triphosphate; D010088:Oxidoreductases; C022398:phytoene dehydrogenase; D014166:Transferases; D019883:Alkyl and Aryl Transferases; D051231:Farnesyltranstransferase; D051232:Geranylgeranyl-Diphosphate Geranylgeranyltransferase; D007535:Isomerases; D019753:Intramolecular Lyases; C070925:lycopene cyclase-isomerase