title: Identification of the SecA protein homolog in pea chloroplasts and its possible involvement in thylakoidal protein transport.
abstract: Recently, we identified the SecA and SecY proteins in the cyanobacterium Synechococcus PCC7942. Antibodies raised against cyanobacterial SecA specifically reacted with a 110-kDa protein of pea chloroplasts, suggesting the presence of SecA in higher plant chloroplasts. A part of the pea secA cDNA was polymerase chain reaction-amplified with degenerated oligonucleotide primers and with pea cDNA as a template. The deduced amino acid sequence shows 62% identity with cyanobacterial SecA and 52% identity with Escherichia coli SecA. Antibodies raised against the pea SecA fragment, which was expressed in E. coli cells from the obtained polymerase chain reaction-amplified cDNA, reacted with the 110-kDa chloroplast protein; the 110-kDa protein was mainly found in the stroma but partly in the thylakoid membrane. The anti-pea SecA IgG inhibited the in vitro import of the 33-kDa protein of the oxygen-evolving complex, but not of the 23-kDa protein of the oxygen-evolving complex, into thylakoids. These results suggest that SecA facilitates transport of a subset of thylakoid lumenal proteins including the 33-kDa protein into thylakoids. We propose that a bacterial-type Sec protein-dependent transport system operates for protein transport into thylakoids in higher plant chloroplasts.
authors.affiliation: Department of Chemistry, Faculty of Science, Nagoya University, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Nakai
authors.forename: A
authors.initials: A
authors.lastname: Goto
authors.forename: T
authors.initials: T
authors.lastname: Nohara
authors.forename: D
authors.initials: D
authors.lastname: Sugita
authors.forename: T
authors.initials: T
authors.lastname: Endo
mesh_terms: D000595:Amino Acid Sequence; D001692:Biological Transport; D015153:Blotting, Western; D002352:Carrier Proteins / Q000235:genetics* / Q000276:immunology / Q000378:metabolism; D002451:Cell Compartmentation; D060365:Chloroplast Proteins; D002736:Chloroplasts / Q000378:metabolism* / Q000648:ultrastructure; D003001:Cloning, Molecular; D000458:Cyanobacteria / Q000737:chemistry; D017343:Genes, Plant; D008565:Membrane Proteins; D008969:Molecular Sequence Data; D018532:Pisum sativum; D010940:Plant Proteins / Q000235:genetics* / Q000276:immunology / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
chemical_list: D002352:Carrier Proteins; D060365:Chloroplast Proteins; D008565:Membrane Proteins; D010940:Plant Proteins; D011506:Proteins