title: Conservative sorting in a primitive plastid. The cyanelle of Cyanophora paradoxa.
abstract: Higher plant chloroplasts possess at least four different pathways for protein translocation across and protein integration into the thylakoid membranes. It is of interest with respect to plastid evolution, which pathways have been retained as a relic from the cyanobacterial ancestor ('conservative sorting'), which ones have been kept but modified, and which ones were developed at the organelle stage, i.e. are eukaryotic achievements as (largely) the Toc and Tic translocons for envelope import of cytosolic precursor proteins. In the absence of data on cyanobacterial protein translocation, the cyanelles of the glaucocystophyte alga Cyanophora paradoxa for which in vitro systems for protein import and intraorganellar sorting were elaborated can serve as a model: the cyanelles are surrounded by a peptidoglycan wall, their thylakoids are covered with phycobilisomes and the composition of their oxygen-evolving complex is another feature shared with cyanobacteria. We demonstrate the operation of the Sec and Tat pathways in cyanelles and show for the first time in vitro protein import across cyanobacteria-like thylakoid membranes and protease protection of the mature protein.
authors.affiliation: Max F. Perutz Laboratories, University Departments at the Vienna Biocenter, Department of Biochemistry and Molecular Cell Biology and Ludwig Boltzmann Research Unit for Biochemistry, Vienna, Austria.
authors.forename: Juergen M
authors.initials: JM
authors.lastname: Steiner
authors.forename: Juergen
authors.initials: J
authors.lastname: Berghöfer
authors.forename: Fumie
authors.initials: F
authors.lastname: Yusa
authors.forename: Johannes A
authors.initials: JA
authors.lastname: Pompe
authors.forename: Ralf B
authors.initials: RB
authors.lastname: Klösgen
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Löffelhardt
mesh_terms: D020418:Algal Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D000595:Amino Acid Sequence; D002736:Chloroplasts / Q000378:metabolism*; D044424:Cyanophora / Q000187:drug effects / Q000378:metabolism*; D045365:Cytochromes c6 / Q000378:metabolism; D014450:Electron Transport Complex III / Q000378:metabolism; D007506:Iron-Sulfur Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D021381:Protein Transport / Q000502:physiology; D011506:Proteins / Q000378:metabolism; D016415:Sequence Alignment; D019810:Sodium Azide / Q000494:pharmacology; D020524:Thylakoids / Q000378:metabolism
chemical_list: D020418:Algal Proteins; D045365:Cytochromes c6; D007506:Iron-Sulfur Proteins; D011506:Proteins; C037989:Rieske iron-sulfur protein; D019810:Sodium Azide; D014450:Electron Transport Complex III