A Homolog of Prokaryotic Thiol Disulfide Transporter CcdA Is Required for the Assembly of the Cytochrome b6f Complex in Arabidopsis Chloroplasts

• Published in: The Journal of biological chemistry Vol. 279; no. 31; pp. 32474 - 32482
• Main Authors: Page, M L Dudley, Hamel, Patrice P, Gabilly, Stéphane T, Zegzouti, Hicham, Perea, John V, Alonso, José M, Ecker, Joseph R, Theg, Steven M, Christensen, Sioux K, Merchant, Sabeeha
• Format: Journal Article
• Language: English
• Published: United States American Society for Biochemistry and Molecular Biology 30.07.2004
• Subjects: Alkaline Phosphatase; Amino Acid Motifs; Arabidopsis - metabolism; Arabidopsis Proteins - chemistry; Arabidopsis Proteins - metabolism; Bacterial Proteins - chemistry; Cell Membrane - metabolism; Chloroplasts - metabolism; Cyclin-Dependent Kinases - chemistry; Cytochrome b6f Complex - metabolism; Cytochromes - chemistry; Cytochromes - metabolism; Cytochromes f - chemistry; Disulfides - chemistry; Lac Operon; Membrane Proteins - chemistry; Membrane Proteins - metabolism; Models, Genetic; Mutation; Peptides - chemistry; Photosynthesis; Plastids - metabolism; Protein Conformation; Protein Structure, Tertiary; RNA, Messenger - metabolism; Sulfhydryl Compounds; Time Factors
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M404285200

The c -type cytochromes are defined by the occurrence of heme covalently linked to the polypeptide via thioether bonds between heme and the cysteine sulfhydryls in the C XX CH motif of apocytochrome. Maintenance of apocytochrome sulfhydryls in a reduced state is a prerequisite for covalent ligation of heme to the C XX CH motif. In bacteria, a thiol disulfide transporter and a thioredoxin are two components in a thio-reduction pathway involved in c -type cytochrome assembly. We have identified in photosynthetic eukaryotes nucleus-encoded homologs of a prokaryotic thiol disulfide transporter, CcdA, which all display an N-terminal extension with respect to their bacterial counterparts. The extension of Arabidopsis CCDA functions as a targeting sequence, suggesting a plastid site of action for CCDA in eukaryotes. Using PhoA and LacZ as topological reporters, we established that Arabidopsis CCDA is a polytopic protein with within-membrane strictly conserved cysteine residues. Insertional mutants in the Arabidopsis CCDA gene were identified, and loss-of-function alleles were shown to impair photosynthesis because of a defect in cytochrome b 6 f accumulation, which we attribute to a block in the maturation of holocytochrome f , whose heme binding domain resides in the thylakoid lumen. We postulate that plastid cytochrome c maturation requires CCDA , thioredoxin HCF164, and other molecules in a membrane-associated trans-thylakoid thiol-reducing pathway.