title: A homolog of prokaryotic thiol disulfide transporter CcdA is required for the assembly of the cytochrome b6f complex in Arabidopsis chloroplasts.
abstract: 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 CXXCH motif of apocytochrome. Maintenance of apocytochrome sulfhydryls in a reduced state is a prerequisite for covalent ligation of heme to the CXXCH 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.
authors.affiliation: Department of Chemistry and Biochemistry, UCLA, Los Angeles, CA 90095, USA.
authors.forename: M L Dudley
authors.initials: ML
authors.lastname: Page
authors.forename: Patrice P
authors.initials: PP
authors.lastname: Hamel
authors.forename: Stéphane T
authors.initials: ST
authors.lastname: Gabilly
authors.forename: Hicham
authors.initials: H
authors.lastname: Zegzouti
authors.forename: John V
authors.initials: JV
authors.lastname: Perea
authors.forename: José M
authors.initials: JM
authors.lastname: Alonso
authors.forename: Joseph R
authors.initials: JR
authors.lastname: Ecker
authors.forename: Steven M
authors.initials: SM
authors.lastname: Theg
authors.forename: Sioux K
authors.initials: SK
authors.lastname: Christensen
authors.forename: Sabeeha
authors.initials: S
authors.lastname: Merchant
mesh_terms: D000469:Alkaline Phosphatase; D020816:Amino Acid Motifs; D017360:Arabidopsis / Q000378:metabolism*; D029681:Arabidopsis Proteins / Q000737:chemistry* / Q000378:metabolism; D001426:Bacterial Proteins / Q000737:chemistry*; D002462:Cell Membrane / Q000378:metabolism; D002736:Chloroplasts / Q000378:metabolism*; D018844:Cyclin-Dependent Kinases / Q000737:chemistry; D045346:Cytochrome b6f Complex / Q000378:metabolism*; D003580:Cytochromes / Q000737:chemistry / Q000378:metabolism; D045348:Cytochromes f / Q000737:chemistry; D004220:Disulfides / Q000737:chemistry; D007763:Lac Operon; D008565:Membrane Proteins / Q000737:chemistry* / Q000378:metabolism; D008957:Models, Genetic; D009154:Mutation; D010455:Peptides / Q000737:chemistry; D010788:Photosynthesis; D018087:Plastids / Q000378:metabolism; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000378:metabolism; D013438:Sulfhydryl Compounds; D013997:Time Factors
chemical_list: D029681:Arabidopsis Proteins; D001426:Bacterial Proteins; C489148:CcdA protein, Arabidopsis; C068355:CcdA protein, Bacteria; D003580:Cytochromes; D004220:Disulfides; D008565:Membrane Proteins; D010455:Peptides; D012333:RNA, Messenger; D013438:Sulfhydryl Compounds; D045346:Cytochrome b6f Complex; D045348:Cytochromes f; D018844:Cyclin-Dependent Kinases; D000469:Alkaline Phosphatase