title: Chloroplast SRP54 Was Recruited for Posttranslational Protein Transport via Complex Formation with Chloroplast SRP43 during Land Plant Evolution.
abstract: In bacteria, membrane proteins are targeted cotranslationally via a signal recognition particle (SRP). During the evolution of higher plant chloroplasts from cyanobacteria, the SRP pathway underwent striking adaptations that enable the posttranslational transport of the abundant light-harvesting chlorophyll-a/b-binding proteins (LHCPs). The conserved 54-kDa SRP subunit in higher plant chloroplasts (cpSRP54) is not bound to an SRP RNA, an essential SRP component in bacteria, but forms a stable heterodimer with the chloroplast-specific cpSRP43. This heterodimeric cpSRP recognizes LHCP and delivers it to the thylakoid membrane whereby cpSRP43 plays a central role. This study shows that the cpSRP system in the green alga Chlamydomonas reinhardtii differs significantly from that of higher plants as cpSRP43 is not complexed to cpSRP54 in Chlamydomonas and cpSRP54 is not involved in LHCP recognition. This divergence is attributed to altered residues within the cpSRP54 tail and the second chromodomain of cpSRP43 that are crucial for the formation of the binding interface in Arabidopsis. These changes are highly conserved among chlorophytes, whereas all land plants contain cpSRP proteins with typical interaction motifs. These data demonstrate that the coevolution of LHCPs and cpSRP43 occurred independently of complex formation with cpSRP54 and that the interaction between cpSRP54 and cpSRP43 evolved later during the transition from chlorophytes to land plants. Furthermore, our data show that in higher plants a heterodimeric form of cpSRP is required for the formation of a low molecular weight transit complex with LHCP.
authors.affiliation: From the Molecular Biology of Plant Organelles and.
authors.forename: Beatrix
authors.initials: B
authors.lastname: Dünschede
authors.affiliation: From the Molecular Biology of Plant Organelles and.
authors.forename: Chantal
authors.initials: C
authors.lastname: Träger
authors.affiliation: From the Molecular Biology of Plant Organelles and.
authors.forename: Christine Vera
authors.initials: CV
authors.lastname: Schröder
authors.affiliation: From the Molecular Biology of Plant Organelles and.
authors.forename: Dominik
authors.initials: D
authors.lastname: Ziehe
authors.affiliation: From the Molecular Biology of Plant Organelles and.
authors.forename: Björn
authors.initials: B
authors.lastname: Walter
authors.affiliation: From the Molecular Biology of Plant Organelles and.
authors.forename: Silke
authors.initials: S
authors.lastname: Funke
authors.affiliation: Protein Crystallography, Ruhr University Bochum, 44780 Bochum, Germany.
authors.forename: Eckhard
authors.initials: E
authors.lastname: Hofmann
authors.affiliation: From the Molecular Biology of Plant Organelles and Danja.Schuenemann@rub.de.
authors.forename: Danja
authors.initials: D
authors.lastname: Schünemann
mesh_terms: D000595:Amino Acid Sequence; D029681:Arabidopsis Proteins / Q000378:metabolism; D001665:Binding Sites; D016825:Chlamydomonas reinhardtii / Q000254:growth & development / Q000378:metabolism*; D060365:Chloroplast Proteins / Q000378:metabolism*; D002736:Chloroplasts / Q000378:metabolism*; D019669:Embryophyta; D019204:GTP-Binding Proteins / Q000378:metabolism; D047468:Immunoprecipitation; D045342:Light-Harvesting Protein Complexes / Q000378:metabolism*; D008969:Molecular Sequence Data; D011485:Protein Binding; D011499:Protein Processing, Post-Translational; D021381:Protein Transport; D017386:Sequence Homology, Amino Acid; D018271:Signal Recognition Particle / Q000378:metabolism*; D020524:Thylakoids / Q000378:metabolism*; D020798:Two-Hybrid System Techniques
chemical_list: D029681:Arabidopsis Proteins; D060365:Chloroplast Proteins; D045342:Light-Harvesting Protein Complexes; C091479:SRP54A protein, Arabidopsis; D018271:Signal Recognition Particle; D019204:GTP-Binding Proteins
keywords: Chlamydomonas; LHCP; chloroplast; protein evolution; protein targeting; signal recognition particle (SRP)
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