title: Targeting of the GTPase Irgm1 to the phagosomal membrane via PtdIns(3,4)P(2) and PtdIns(3,4,5)P(3) promotes immunity to mycobacteria.
abstract: Vertebrate immunity to infection enlists a newly identified family of 47-kilodalton immunity-related GTPases (IRGs). One IRG in particular, Irgm1, is essential for macrophage host defense against phagosomal pathogens, including Mycobacterium tuberculosis (Mtb). Here we show that Irgm1 targets the mycobacterial phagosome through lipid-mediated interactions with phosphatidylinositol-3,4-bisphosphate (PtdIns(3,4)P(2)) and PtdIns(3,4,5)P(3). An isolated Irgm1 amphipathic helix conferred lipid binding in vitro and in vivo. Substitutions in this region blocked phagosome recruitment and failed to complement the antimicrobial defect in Irgm1(-/-) macrophages. Removal of PtdIns(3,4,5)P(3) or inhibition of class I phosphatidylinositol-3-OH kinase (PI(3)K) mimicked this effect in wild-type cells. Cooperation between Irgm1 and PI(3)K further facilitated the engagement of Irgm1 with its fusogenic effectors at the site of infection, thereby ensuring pathogen-directed responses during innate immunity.
authors.affiliation: Boyer Center for Molecular Medicine, Yale University School of Medicine, New Haven, Connecticut, USA.
authors.forename: Sangeeta
authors.initials: S
authors.lastname: Tiwari
authors.forename: Han-Pil
authors.initials: HP
authors.lastname: Choi
authors.forename: Takeshi
authors.initials: T
authors.lastname: Matsuzawa
authors.forename: Marc
authors.initials: M
authors.lastname: Pypaert
authors.forename: John D
authors.initials: JD
authors.lastname: MacMicking
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D019204:GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D007113:Immunity, Innate; D007371:Interferon-gamma / Q000502:physiology; D007425:Intracellular Membranes / Q000378:metabolism; D008247:Lysosomes / Q000378:metabolism; D008264:Macrophages / Q000276:immunology / Q000378:metabolism / Q000382:microbiology; D051379:Mice; D009169:Mycobacterium tuberculosis / Q000276:immunology / Q000502:physiology*; D010588:Phagosomes / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism*; D011485:Protein Binding; D017433:Protein Structure, Secondary; D021381:Protein Transport / Q000502:physiology; D050600:SNARE Proteins / Q000378:metabolism; D015398:Signal Transduction
chemical_list: C096000:Ifi1 protein, mouse; D018129:Phosphatidylinositol Phosphates; D050600:SNARE Proteins; C060974:phosphatidylinositol 3,4,5-triphosphate; C060980:phosphatidylinositol 3,4-diphosphate; D007371:Interferon-gamma; D019869:Phosphatidylinositol 3-Kinases; D019204:GTP-Binding Proteins