title: The TL29 protein is lumen located, associated with PSII and not an ascorbate peroxidase.
abstract: The TL29 protein is one of the more abundant proteins in the thylakoid lumen of plant chloroplasts. Based on its sequence homology to ascorbate peroxidases, but without any supporting biochemical evidence, TL29 was suggested to be involved in the plant defense system against reactive oxygen species and consequently renamed to APX4. Our in vivo and in vitro analyses failed to show any peroxidase activity associated with TL29; it bound neither heme nor ascorbate. Recombinant overexpressed TL29 had no ascorbate-dependent peroxidase activity, and various mutational analyses aiming to convert TL29 into an ascorbate peroxidase failed. Furthermore, in the thylakoid lumen no such activity could be associated with TL29 and, additionally, TL29 knock-out mutants did not show any decreased peroxidase activity or increased content of radical oxygen species when grown under light stress. Instead we could show that TL29 is a lumen-located component associated with PSII.
authors.affiliation: Department of Forest Genetics and Plant Physiology, Swedish University of Agricultural Sciences, SE-901 83 Umeå, Sweden.
authors.forename: Irene
authors.initials: I
authors.lastname: Granlund
authors.forename: Patrik
authors.initials: P
authors.lastname: Storm
authors.forename: Maria
authors.initials: M
authors.lastname: Schubert
authors.forename: José G
authors.initials: JG
authors.lastname: García-Cerdán
authors.forename: Christiane
authors.initials: C
authors.lastname: Funk
authors.forename: Wolfgang P
authors.initials: WP
authors.lastname: Schröder
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D060387:Ascorbate Peroxidases; D001205:Ascorbic Acid / Q000032:analysis; D004269:DNA, Bacterial / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics; D018506:Gene Expression Regulation, Plant; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D010544:Peroxidases / Q000378:metabolism; D045332:Photosystem II Protein Complex / Q000378:metabolism*; D017382:Reactive Oxygen Species / Q000032:analysis; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D020524:Thylakoids / Q000235:genetics / Q000378:metabolism*
chemical_list: D029681:Arabidopsis Proteins; D004269:DNA, Bacterial; D018076:DNA, Complementary; D008565:Membrane Proteins; D045332:Photosystem II Protein Complex; D017382:Reactive Oxygen Species; C036483:T-DNA; D010544:Peroxidases; D060387:Ascorbate Peroxidases; D001205:Ascorbic Acid