title: High-resolution dissection of phagosome maturation reveals distinct membrane trafficking phases.
abstract: Molecular mechanisms of endocytosis in the genetically and biochemically tractable professional phagocyte Dictyostelium discoideum reveal a striking degree of similarity to higher eukaryotic cells. Pulse-chase feeding with latex beads allowed purification of phagosomes at different stages of maturation. Gentle ATP stripping of an actin meshwork entrapping contaminating organelles resulted in a 10-fold increase in yield and purity, as confirmed by electron microscopy. Temporal profiling of signaling, cytoskeletal, and trafficking proteins resulted in a complex molecular fingerprint of phagosome biogenesis and maturation. First, nascent phagosomes were associated with coronin and rapidly received a lysosomal glycoprotein, LmpB. Second, at least two phases of delivery of lysosomal hydrolases (cathepsin D [CatD] and cysteine protease [CPp34]) were accompanied by removal of plasma membrane components (PM4C4 and biotinylated surface proteins). Third, a phase of late maturation, preparing for final exocytosis of undigested material, included quantitative recycling of hydrolases and association with vacuolin. Also, lysosomal glycoproteins of the Lmp family showed distinct trafficking kinetics. The delivery and recycling of CatD was directly visualized by confocal microscopy. This heavy membrane traffic of cargos was precisely accompanied by regulatory proteins such as the Rab7 GTPases and the endosomal SNAREs Vti1 and VAMP7. This initial molecular description of phagocytosis demonstrates the feasibility of a comprehensive analysis of phagosomal lipids and proteins in genetically modified strains.
authors.affiliation: Department of Molecular Cell Research, Max-Planck-Institute for Medical Research, D-69120 Heidelberg, Germany.
authors.forename: Daniel
authors.initials: D
authors.lastname: Gotthardt
authors.forename: Hans Jörg
authors.initials: HJ
authors.lastname: Warnatz
authors.forename: Oliver
authors.initials: O
authors.lastname: Henschel
authors.forename: Franz
authors.initials: F
authors.lastname: Brückert
authors.forename: Michael
authors.initials: M
authors.lastname: Schleicher
authors.forename: Thierry
authors.initials: T
authors.lastname: Soldati
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001692:Biological Transport / Q000502:physiology*; D015415:Biomarkers; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000378:metabolism; D002352:Carrier Proteins / Q000378:metabolism; D002402:Cathepsin D / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry / Q000378:metabolism*; D004023:Dictyostelium / Q000166:cytology / Q000378:metabolism*; D004705:Endocytosis / Q000502:physiology; D005456:Fluorescent Dyes / Q000378:metabolism; D028884:Karyopherins / Q000378:metabolism; D050356:Lipid Metabolism; D008055:Lipids / Q000737:chemistry; D008565:Membrane Proteins / Q000378:metabolism; D008840:Microfilament Proteins / Q000378:metabolism; D010588:Phagosomes / Q000737:chemistry / Q000378:metabolism* / Q000648:ultrastructure; D011506:Proteins / Q000737:chemistry / Q000378:metabolism; D050766:Qb-SNARE Proteins; D050683:R-SNARE Proteins; D050600:SNARE Proteins; D013844:Thiazoles / Q000378:metabolism; D053778:Thiazolidines; D033921:Vesicular Transport Proteins; D020691:rab GTP-Binding Proteins / Q000378:metabolism; D000090802:rab7 GTP-Binding Proteins
chemical_list: D015415:Biomarkers; D019086:Bridged Bicyclo Compounds, Heterocyclic; D002352:Carrier Proteins; D005456:Fluorescent Dyes; D028884:Karyopherins; D008055:Lipids; D008565:Membrane Proteins; D008840:Microfilament Proteins; D011506:Proteins; D050766:Qb-SNARE Proteins; D050683:R-SNARE Proteins; D050600:SNARE Proteins; D013844:Thiazoles; D053778:Thiazolidines; C121241:VAMP7 protein, human; C491419:VTI1A protein, human; D033921:Vesicular Transport Proteins; C018589:lysosomal proteins; D000090802:rab7 GTP-Binding Proteins; C000716463:rab7 GTP-binding proteins, human; C072061:coronin proteins; D000255:Adenosine Triphosphate; D002402:Cathepsin D; D020691:rab GTP-Binding Proteins; C037068:latrunculin B