title: Protein trafficking to the plastid of Plasmodium falciparum is via the secretory pathway.
abstract: The plastid of Plasmodium falciparum (or 'apicoplast') is the evolutionary homolog of the plant chloroplast and represents a vestige of a photosynthetic past. Apicoplast indispensability indicates that it still provides essential functions to parasites. Similar to plant chloroplasts, the apicoplast is dependent on many nucleus-encoded genes to provide these functions. The apicoplast is surrounded by four membranes, two more than plant chloroplasts. Thus, protein targeting to the apicoplast must overcome additional membrane barriers. In P.falciparum we have analyzed apicoplast targeting using green fluorescent protein (GFP). We demonstrate that protein targeting is at least a two-step process mediated by bipartite N-terminal pre-sequences that consist of a signal peptide for entry into the secretory pathway and a plant-like transit peptide for subsequent import into the apicoplast. The P.falciparum transit peptide is exceptional compared with other known plastid transit peptides in not requiring serine or threonine residues. The pre-sequence components are removed stepwise during apicoplast targeting. Targeting GFP to the apicoplast has also provided the first opportunity to examine apicoplast morphology in live P. falciparum.
authors.affiliation: Plant Cell Biology Research Centre, School of Botany, University of Melbourne, Parkville Victoria 3052, Australia. r.waller@pgrad.u
authors.forename: R F
authors.initials: RF
authors.lastname: Waller
authors.forename: M B
authors.initials: MB
authors.lastname: Reed
authors.forename: A F
authors.initials: AF
authors.lastname: Cowman
authors.forename: G I
authors.initials: GI
authors.lastname: McFadden
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D015153:Blotting, Western; D004912:Erythrocytes / Q000469:parasitology; D049452:Green Fluorescent Proteins; D006801:Humans; D008164:Luminescent Proteins / Q000378:metabolism; D018613:Microscopy, Confocal; D008969:Molecular Sequence Data; D009154:Mutation; D010455:Peptides / Q000378:metabolism*; D010963:Plasmodium falciparum / Q000235:genetics / Q000378:metabolism*; D018087:Plastids / Q000378:metabolism*; D021382:Protein Sorting Signals / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D014170:Transformation, Genetic; D019076:Transgenes / Q000235:genetics; D014617:Vacuoles / Q000378:metabolism
chemical_list: D008164:Luminescent Proteins; D010455:Peptides; D021382:Protein Sorting Signals; D049452:Green Fluorescent Proteins