title: Chloroplast FtsY, chloroplast signal recognition particle, and GTP are required to reconstitute the soluble phase of light-harvesting chlorophyll protein transport into thylakoid membranes.
abstract: The integration of light-harvesting chlorophyll proteins (LHCPs) into the thylakoid membrane proceeds in two steps. First, LHCP interacts with a chloroplast signal recognition particle (cpSRP) to form a soluble targeting intermediate called the transit complex. Second, LHCP integrates into the thylakoid membrane in the presence of GTP, at least one other soluble factor, and undefined membrane components. We previously determined that cpSRP is composed of 43- and 54-kDa polypeptides. We have examined the subunit stoichiometry of cpSRP and find that it is trimeric and composed of two subunits of cpSRP43/subunit of cpSRP54. A chloroplast homologue of FtsY, an Escherichia coli protein that is critical for the function of E. coli SRP, was found largely in the stroma unassociated with cpSRP. When chloroplast FtsY was combined with cpSRP and GTP, the three factors promoted efficient LHCP integration into thylakoid membranes in the absence of stroma, demonstrating that they are all required for reconstituting the soluble phase of LHCP transport.
authors.affiliation: Department of Plant Biology, Carnegie Institution of Washington, Stanford, California 94305, USA.
authors.forename: C J
authors.initials: CJ
authors.lastname: Tu
authors.forename: D
authors.initials: D
authors.lastname: Schuenemann
authors.forename: N E
authors.initials: NE
authors.lastname: Hoffman
mesh_terms: D000595:Amino Acid Sequence; D017360:Arabidopsis; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D001693:Biological Transport, Active; D019281:Dimerization; D004926:Escherichia coli; D006160:Guanosine Triphosphate / Q000378:metabolism*; D045342:Light-Harvesting Protein Complexes; D008969:Molecular Sequence Data; D045322:Photosynthetic Reaction Center Complex Proteins / Q000235:genetics*; D010944:Plants; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism*; D016415:Sequence Alignment
chemical_list: D001426:Bacterial Proteins; C087406:FtsY protein, Bacteria; D045342:Light-Harvesting Protein Complexes; D045322:Photosynthetic Reaction Center Complex Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D006160:Guanosine Triphosphate