title: The Trypanosome Exocyst: A Conserved Structure Revealing a New Role in Endocytosis.
abstract: Membrane transport is an essential component of pathogenesis for most infectious organisms. In African trypanosomes, transport to and from the plasma membrane is closely coupled to immune evasion and antigenic variation. In mammals and fungi an octameric exocyst complex mediates late steps in exocytosis, but comparative genomics suggested that trypanosomes retain only six canonical subunits, implying mechanistic divergence. We directly determined the composition of the Trypanosoma brucei exocyst by affinity isolation and demonstrate that the parasite complex is nonameric, retaining all eight canonical subunits (albeit highly divergent at the sequence level) plus a novel essential subunit, Exo99. Exo99 and Sec15 knockdowns have remarkably similar phenotypes in terms of viability and impact on morphology and trafficking pathways. Significantly, both Sec15 and Exo99 have a clear function in endocytosis, and global proteomic analysis indicates an important role in maintaining the surface proteome. Taken together these data indicate additional exocyst functions in trypanosomes, which likely include endocytosis, recycling and control of surface composition. Knockdowns in HeLa cells suggest that the role in endocytosis is shared with metazoan cells. We conclude that, whilst the trypanosome exocyst has novel components, overall functionality appears conserved, and suggest that the unique subunit may provide therapeutic opportunities.
authors.affiliation: Wellcome Trust Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dow Street, Dundee, United Kingdom.
authors.forename: Cordula M
authors.initials: CM
authors.lastname: Boehm
authors.affiliation: The Rockefeller University, 1230 York Avenue, New York, NY, United States of America.
authors.forename: Samson
authors.initials: S
authors.lastname: Obado
authors.affiliation: School of Life Sciences, University of Nottingham, Nottingham, United Kingdom.
authors.forename: Catarina
authors.initials: C
authors.lastname: Gadelha
authors.affiliation: Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom.
authors.forename: Alexandra
authors.initials: A
authors.lastname: Kaupisch
authors.affiliation: Wellcome Trust Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dow Street, Dundee, United Kingdom.
authors.forename: Paul T
authors.initials: PT
authors.lastname: Manna
authors.affiliation: Institute of Molecular, Cell and Systems Biology, College of Medical, Veterinary and Life Sciences, University of Glasgow, Glasgow, United Kingdom.
authors.forename: Gwyn W
authors.initials: GW
authors.lastname: Gould
authors.affiliation: Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical School, Worcester, MA, United States of America.
authors.forename: Mary
authors.identifier: 0000-0003-2297-8053
authors.initials: M
authors.lastname: Munson
authors.affiliation: The Rockefeller University, 1230 York Avenue, New York, NY, United States of America.
authors.forename: Brian T
authors.identifier: 0000-0003-3524-557X
authors.initials: BT
authors.lastname: Chait
authors.affiliation: The Rockefeller University, 1230 York Avenue, New York, NY, United States of America.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Rout
authors.affiliation: Wellcome Trust Centre for Anti-Infectives Research, School of Life Sciences, University of Dundee, Dow Street, Dundee, United Kingdom.
authors.forename: Mark C
authors.initials: MC
authors.lastname: Field
mesh_terms: D005075:Biological Evolution; D015153:Blotting, Western; D002462:Cell Membrane / Q000378:metabolism; D004705:Endocytosis / Q000502:physiology*; D006367:HeLa Cells; D006801:Humans; D046529:Microscopy, Electron, Transmission; D008856:Microscopy, Fluorescence; D016133:Polymerase Chain Reaction; D021381:Protein Transport / Q000502:physiology; D040901:Proteomics; D015800:Protozoan Proteins / Q000378:metabolism; D014346:Trypanosoma brucei brucei / Q000472:pathogenicity*
chemical_list: D015800:Protozoan Proteins