title: Anaplasma phagocytophilum Ats-1 is imported into host cell mitochondria and interferes with apoptosis induction.
abstract: Anaplasma phagocytophilum, the causative agent of human granulocytic anaplasmosis, infects human neutrophils and inhibits mitochondria-mediated apoptosis. Bacterial factors involved in this process are unknown. In the present study, we screened a genomic DNA library of A. phagocytophilum for effectors of the type IV secretion system by a bacterial two-hybrid system, using A. phagocytophilum VirD4 as bait. A hypothetical protein was identified as a putative effector, hereby named Anaplasmatranslocated substrate 1 (Ats-1). Using triple immunofluorescence labeling and Western blot analysis of infected cells, including human neutrophils, we determined that Ats-1 is abundantly expressed by A. phagocytophilum, translocated across the inclusion membrane, localized in the host cell mitochondria, and cleaved. Ectopically expressed Ats-1 targeted mitochondria in an N-terminal 17 residue-dependent manner, localized in matrix or at the inner membrane, and was cleaved as native protein, which required residues 55-57. In vitro-translated Ats-1 was imported in a receptor-dependent manner into isolated mitochondria. Ats-1 inhibited etoposide-induced cytochrome c release from mitochondria, PARP cleavage, and apoptosis in mammalian cells, as well as Bax-induced yeast apoptosis. Ats-1(55-57) had significantly reduced anti-apoptotic activity. Bax redistribution was inhibited in both etoposide-induced and Bax-induced apoptosis by Ats-1. Taken together, Ats-1 is the first example of a bacterial protein that traverses five membranes and prevents apoptosis at the mitochondria.
authors.affiliation: Department of Veterinary Biosciences, The Ohio State University, Columbus, Ohio, USA.
authors.forename: Hua
authors.initials: H
authors.lastname: Niu
authors.forename: Vera
authors.initials: V
authors.lastname: Kozjak-Pavlovic
authors.forename: Thomas
authors.initials: T
authors.lastname: Rudel
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Rikihisa
mesh_terms: D041081:Anaplasma phagocytophilum / Q000378:metabolism*; D017209:Apoptosis / Q000502:physiology*; D001426:Bacterial Proteins / Q000378:metabolism*; D015153:Blotting, Western; D002460:Cell Line; D016873:Ehrlichiosis / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D005798:Genes, Bacterial; D018922:HL-60 Cells; D006801:Humans; D013058:Mass Spectrometry; D008928:Mitochondria / Q000378:metabolism* / Q000382:microbiology; D009504:Neutrophils / Q000382:microbiology; D021381:Protein Transport; D020798:Two-Hybrid System Techniques
chemical_list: D001426:Bacterial Proteins