title: A thylakoid membrane protein harboring a DnaJ-type zinc finger domain is required for photosystem I accumulation in plants.
abstract: Photosystem I (PSI) is a large pigment-protein complex and one of the two photosystems that drive electron transfer in oxygenic photosynthesis. We identified a nuclear gene required specifically for the accumulation of PSI in a forward genetic analysis of chloroplast biogenesis in maize. This gene, designated psa2, belongs to the "GreenCut" gene set, a group of genes found in green algae and plants but not in non-photosynthetic organisms. Disruption of the psa2 ortholog in Arabidopsis likewise resulted in the specific loss of PSI proteins. PSA2 harbors a conserved domain found in DnaJ chaperones where it has been shown to form a zinc finger and to have protein-disulfide isomerase activity. Accordingly, PSA2 exhibited protein-disulfide reductase activity in vitro. PSA2 localized to the thylakoid lumen and was found in a ∼250-kDa complex harboring the peripheral PSI protein PsaG but lacking several core PSI subunits. PSA2 mRNA is coexpressed with mRNAs encoding various proteins involved in the biogenesis of the photosynthetic apparatus with peak expression preceding that of genes encoding structural components. PSA2 protein abundance was not decreased in the absence of PSI but was reduced in the absence of the PSI assembly factor Ycf3. These findings suggest that a complex harboring PSA2 and PsaG mediates thiol transactions in the thylakoid lumen that are important for the assembly of PSI.
authors.affiliation: Department of Chemistry and Biochemistry and UCLA, Los Angeles, California 90095; Institute for Genomics and Proteomics, UCLA, Los Angeles, California 90095 and.
authors.forename: Rikard
authors.initials: R
authors.lastname: Fristedt
authors.affiliation: Institute of Molecular Biology, University of Oregon, Eugene, Oregon 97403.
authors.forename: Rosalind
authors.initials: R
authors.lastname: Williams-Carrier
authors.affiliation: Department of Chemistry and Biochemistry and UCLA, Los Angeles, California 90095; Institute for Genomics and Proteomics, UCLA, Los Angeles, California 90095 and.
authors.forename: Sabeeha S
authors.initials: SS
authors.lastname: Merchant
authors.affiliation: Institute of Molecular Biology, University of Oregon, Eugene, Oregon 97403. Electronic address: abarkan@uoregon.edu.
authors.forename: Alice
authors.initials: A
authors.lastname: Barkan
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000737:chemistry / Q000502:physiology*; D001483:Base Sequence; D002734:Chlorophyll / Q000378:metabolism; D003553:Cystine / Q000737:chemistry; D055786:Gene Knockout Techniques; D007700:Kinetics; D008969:Molecular Sequence Data; D010084:Oxidation-Reduction; D010788:Photosynthesis; D045331:Photosystem I Protein Complex / Q000378:metabolism*; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism; D025941:Protein Interaction Mapping; D021381:Protein Transport; D017384:Sequence Deletion; D020524:Thylakoids / Q000378:metabolism; D003313:Zea mays / Q000235:genetics* / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D045331:Photosystem I Protein Complex; C000594047:Psa2 protein, Arabidopsis; D002734:Chlorophyll; D003553:Cystine
keywords: Arabidopsis; Chaperone DnaJ (DnaJ); Chloroplast; Maize; Membrane Biogenesis; Photosynthesis; Protein-disulfide Isomerase; Thylakoid Lumen