title: An apicoplast localized ubiquitylation system is required for the import of nuclear-encoded plastid proteins.
abstract: Apicomplexan parasites are responsible for numerous important human diseases including toxoplasmosis, cryptosporidiosis, and most importantly malaria. There is a constant need for new antimalarials, and one of most keenly pursued drug targets is an ancient algal endosymbiont, the apicoplast. The apicoplast is essential for parasite survival, and several aspects of its metabolism and maintenance have been validated as targets of anti-parasitic drug treatment. Most apicoplast proteins are nuclear encoded and have to be imported into the organelle. Recently, a protein translocon typically required for endoplasmic reticulum associated protein degradation (ERAD) has been proposed to act in apicoplast protein import. Here, we show ubiquitylation to be a conserved and essential component of this process. We identify apicoplast localized ubiquitin activating, conjugating and ligating enzymes in Toxoplasma gondii and Plasmodium falciparum and observe biochemical activity by in vitro reconstitution. Using conditional gene ablation and complementation analysis we link this activity to apicoplast protein import and parasite survival. Our studies suggest ubiquitylation to be a mechanistic requirement of apicoplast protein import independent to the proteasomal degradation pathway.
authors.affiliation: Department of Cellular Biology, University of Georgia, Athens, Georgia, United States of America.
authors.forename: Swati
authors.initials: S
authors.lastname: Agrawal
authors.forename: Duk-Won D
authors.initials: DW
authors.lastname: Chung
authors.forename: Nadia
authors.initials: N
authors.lastname: Ponts
authors.forename: Giel G
authors.initials: GG
authors.lastname: van Dooren
authors.forename: Jacques
authors.initials: J
authors.lastname: Prudhomme
authors.forename: Carrie F
authors.initials: CF
authors.lastname: Brooks
authors.forename: Elisadra M
authors.initials: EM
authors.lastname: Rodrigues
authors.forename: John C
authors.initials: JC
authors.lastname: Tan
authors.forename: Michael T
authors.initials: MT
authors.lastname: Ferdig
authors.forename: Boris
authors.initials: B
authors.lastname: Striepen
authors.forename: Karine G
authors.initials: KG
authors.lastname: Le Roch
mesh_terms: D002460:Cell Line; D060365:Chloroplast Proteins / Q000235:genetics / Q000378:metabolism*; D060746:Endoplasmic Reticulum-Associated Degradation / Q000502:physiology*; D006801:Humans; D010963:Plasmodium falciparum / Q000235:genetics / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism; D021381:Protein Transport / Q000502:physiology; D015800:Protozoan Proteins / Q000235:genetics / Q000378:metabolism*; D014122:Toxoplasma / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination / Q000502:physiology*
chemical_list: D060365:Chloroplast Proteins; D015800:Protozoan Proteins; D046988:Proteasome Endopeptidase Complex