title: Light stress-induced one-helix protein of the chlorophyll a/b-binding family associated with photosystem I.
abstract: The superfamily of light-harvesting chlorophyll a/b-binding (Lhc) proteins in higher plants and green algae is composed of more than 20 different antenna proteins associated either with photosystem I (PSI) or photosystem II (PSII). Several distant relatives of this family with conserved chlorophyll-binding residues and proposed photoprotective functions are induced transiently under various stress conditions. Whereas "classical" Lhc proteins contain three-transmembrane alpha-helices, their distant relatives span the membrane with between one and four transmembrane segments. Here, we report the identification and isolation of a novel member of the Lhc family from Arabidopsis with one predicted transmembrane alpha-helix closely related to helix I of Lhc protein from PSI (Lhca4) that we named Ohp2 (for a second one-helix protein of Lhc family described from higher plants). We showed that the Ohp2 gene expression is triggered by light stress and that the Ohp2 transcript and protein accumulated in a light intensity-dependent manner. Other stress conditions did not up-regulate the expression of the Ohp2 gene. Localization studies revealed that Ohp2 is associated with PSI under low- or high-light conditions. Because all stress-induced Lhc relatives reported so far were found in PSII, we propose that the accumulation of Ohp2 might represent a novel photoprotective strategy induced within PSI in response to light stress.
authors.affiliation: Department of Biochemistry and Biophysics, Arrhenius Laboratories for Natural Sciences, Stockholm University, Sweden.
authors.forename: Ulrica
authors.initials: U
authors.lastname: Andersson
authors.forename: Mounia
authors.initials: M
authors.lastname: Heddad
authors.forename: Iwona
authors.initials: I
authors.lastname: Adamska
mesh_terms: D000595:Amino Acid Sequence; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002736:Chloroplasts / Q000235:genetics / Q000378:metabolism; D003001:Cloning, Molecular; D018506:Gene Expression Regulation, Plant / Q000528:radiation effects; D008027:Light; D045342:Light-Harvesting Protein Complexes; D008969:Molecular Sequence Data; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics / Q000378:metabolism*; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D014176:Protein Biosynthesis; D011487:Protein Conformation; D018749:RNA, Plant / Q000235:genetics / Q000302:isolation & purification; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic
chemical_list: D029681:Arabidopsis Proteins; D045342:Light-Harvesting Protein Complexes; C476764:Ohp2 protein, Arabidopsis; D045322:Photosynthetic Reaction Center Complex Proteins; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D018749:RNA, Plant; D011994:Recombinant Proteins