The chloroplast Rieske iron-sulfur protein. At the crossroad of electron transport and signal transduction

• Published in: The Journal of biological chemistry 2004-10, Vol.279 (43), p.44621-44627
• Main Authors: de Vitry, Catherine, Ouyang, Yexin, Finazzi, Giovanni, Wollman, Francis-André, Kallas, Toivo
• Format: Article
• Language: English
• Subjects: Amino Acid Sequence; Animals; Catalysis; Cell Membrane - metabolism; Cell Nucleus - metabolism; Cell Proliferation; Chlamydomonas reinhardtii; Chlamydomonas reinhardtii - metabolism; Chloroplasts - metabolism; Cytochrome b6f Complex - chemistry; Cytochromes f - metabolism; Electron Transport; Electron Transport Complex III - metabolism; Electrophoresis, Polyacrylamide Gel; Enzyme Activation; Gene Deletion; Iron-Sulfur Proteins - metabolism; Kinetics; Models, Molecular; Molecular Sequence Data; Mutagenesis; Mutagenesis, Site-Directed; Mutation; Oxidation-Reduction; Phenotype; Phosphorylation; Photosystem II Protein Complex - chemistry; Plasmids - metabolism; Protein Conformation; Protein Structure, Tertiary; Signal Transduction; Spectrometry, Fluorescence; Thylakoids - metabolism; Time Factors
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M406955200

We have addressed the functional and structural roles of three domains of the chloroplast Rieske iron-sulfur protein; that is, the flexible hinge that connects the transmembrane helix to the soluble cluster-bearing domain, the N-terminal stromal protruding domain, and the transmembrane helix. To this aim mutants were generated in the green alga Chlamydomonas reinhardtii. Their capacities to assemble the cytochrome b6f complex, perform plastoquinol oxidation, and signal redox-induced activation of the light-harvesting complex II kinase during state transition were tested in vivo. Deletion of one residue and extensions of up to five residues in the flexible hinge had no significant effect on complex accumulation or electron transfer efficiency. Deletion of three residues (Delta3G) dramatically decreased reaction rates by a factor of approximately 10. These data indicate that the chloroplast iron-sulfur protein-linking domain is much more flexible than that of its counterpart in mitochondria. Despite greatly slowed catalysis in the Delta3G mutant, there was no apparent delay in light-harvesting complex II kinase activation or state transitions. This indicates that conformational changes occurring in the Rieske protein did not represent a limiting step for kinase activation within the time scale tested. No phenotype could be associated with mutations in the N-terminal stromal-exposed domain. In contrast, the N17V mutation in the Rieske protein transmembrane helix resulted in a large decrease in the cytochrome f synthesis rate. This reveals that the Rieske protein transmembrane helix plays an active role in assembly-mediated control of cytochrome f synthesis. We propose a structural model to interpret this phenomenon based on the C. reinhardtii cytochrome b6f structure.