title: Targeting of tail-anchored membrane proteins to subcellular organelles in Toxoplasma gondii.
abstract: Proper protein localization is essential for critical cellular processes, including vesicle-mediated transport and protein translocation. Tail-anchored (TA) proteins are integrated into organellar membranes via the C-terminus, orienting the N-terminus towards the cytosol. Localization of TA proteins occurs posttranslationally and is governed by the C-terminus, which contains the integral transmembrane domain (TMD) and targeting sequence. Targeting of TA proteins is dependent on the hydrophobicity of the TMD as well as the length and composition of flanking amino acid sequences. We previously identified an unusual homologue of elongator protein, Elp3, in the apicomplexan parasite Toxoplasma gondii as a TA protein targeting the outer mitochondrial membrane. We sought to gain further insight into TA proteins and their targeting mechanisms using this early-branching eukaryote as a model. Our bioinformatics analysis uncovered 59 predicted TA proteins in Toxoplasma, 9 of which were selected for follow-up analyses based on representative features. We identified novel TA proteins that traffic to specific organelles in Toxoplasma, including the parasite endoplasmic reticulum, mitochondrion, and Golgi apparatus. Domain swap experiments elucidated that targeting of TA proteins to these specific organelles was strongly influenced by the TMD sequence, including charge of the flanking C-terminal sequence.
authors.affiliation: Department of Pharmacology and Toxicology, Indiana University School of Medicine, Indianapolis, Indiana.
authors.forename: Leah R
authors.initials: LR
authors.lastname: Padgett
authors.affiliation: Department of Pharmacology and Toxicology, Indiana University School of Medicine, Indianapolis, Indiana.|Department of Microbiology and Immunology, Indiana University School of Medicine, Indianapolis, Indiana.
authors.forename: Gustavo
authors.initials: G
authors.lastname: Arrizabalaga
authors.affiliation: Department of Pharmacology and Toxicology, Indiana University School of Medicine, Indianapolis, Indiana.|Department of Microbiology and Immunology, Indiana University School of Medicine, Indianapolis, Indiana.
authors.forename: William J
authors.initials: WJ
authors.lastname: Sullivan
mesh_terms: D000595:Amino Acid Sequence; D001692:Biological Transport / Q000502:physiology; D004721:Endoplasmic Reticulum / Q000378:metabolism; D006056:Golgi Apparatus / Q000378:metabolism; D008565:Membrane Proteins / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism; D011485:Protein Binding / Q000502:physiology; D021382:Protein Sorting Signals / Q000502:physiology; D017434:Protein Structure, Tertiary; D021381:Protein Transport / Q000502:physiology*; D015800:Protozoan Proteins / Q000378:metabolism*; D014122:Toxoplasma / Q000378:metabolism*
chemical_list: D008565:Membrane Proteins; D021382:Protein Sorting Signals; D015800:Protozoan Proteins
keywords: Golgi apparatus; endoplasmic reticulum; membrane protein; mitochondria; parasites; protein localization; protein trafficking