title: Analysis of the chloroplast protein kinase Stt7 during state transitions.
abstract: State transitions allow for the balancing of the light excitation energy between photosystem I and photosystem II and for optimal photosynthetic activity when photosynthetic organisms are subjected to changing light conditions. This process is regulated by the redox state of the plastoquinone pool through the Stt7/STN7 protein kinase required for phosphorylation of the light-harvesting complex LHCII and for the reversible displacement of the mobile LHCII between the photosystems. We show that Stt7 is associated with photosynthetic complexes including LHCII, photosystem I, and the cytochrome b6f complex. Our data reveal that Stt7 acts in catalytic amounts. We also provide evidence that Stt7 contains a transmembrane region that separates its catalytic kinase domain on the stromal side from its N-terminal end in the thylakoid lumen with two conserved Cys that are critical for its activity and state transitions. On the basis of these data, we propose that the activity of Stt7 is regulated through its transmembrane domain and that a disulfide bond between the two lumen Cys is essential for its activity. The high-light-induced reduction of this bond may occur through a transthylakoid thiol-reducing pathway driven by the ferredoxin-thioredoxin system which is also required for cytochrome b6f assembly and heme biogenesis.
authors.affiliation: Department of Molecular Biology University of Geneva, Geneva, Switzerland.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Lemeille
authors.forename: Adrian
authors.initials: A
authors.lastname: Willig
authors.forename: Nathalie
authors.initials: N
authors.lastname: Depège-Fargeix
authors.forename: Christian
authors.initials: C
authors.lastname: Delessert
authors.forename: Roberto
authors.initials: R
authors.lastname: Bassi
authors.forename: Jean-David
authors.initials: JD
authors.lastname: Rochaix
mesh_terms: D000222:Adaptation, Physiological; D020418:Algal Proteins / Q000737:chemistry / Q000502:physiology*; D000818:Animals; D002696:Chlamydomonas / Q000201:enzymology / Q000502:physiology*; D002736:Chloroplasts / Q000201:enzymology / Q000502:physiology; D045346:Cytochrome b6f Complex / Q000502:physiology; D008027:Light; D045342:Light-Harvesting Protein Complexes / Q000502:physiology; D010788:Photosynthesis / Q000502:physiology*; D045331:Photosystem I Protein Complex / Q000502:physiology; D045332:Photosystem II Protein Complex / Q000502:physiology; D011487:Protein Conformation; D011494:Protein Kinases / Q000737:chemistry / Q000502:physiology*; D013329:Structure-Activity Relationship
chemical_list: D020418:Algal Proteins; D045342:Light-Harvesting Protein Complexes; D045331:Photosystem I Protein Complex; D045332:Photosystem II Protein Complex; D045346:Cytochrome b6f Complex; D011494:Protein Kinases