title: The Legionella effector SidC defines a unique family of ubiquitin ligases important for bacterial phagosomal remodeling.
abstract: The activity of proteins delivered into host cells by the Dot/Icm injection apparatus allows Legionella pneumophila to establish a niche called the Legionella-containing vacuole (LCV), which is permissive for intracellular bacterial propagation. Among these proteins, substrate of Icm/Dot transporter (SidC) anchors to the cytoplasmic surface of the LCV and is important for the recruitment of host endoplasmic reticulum (ER) proteins to this organelle. However, the biochemical function underlying this activity is unknown. Here, we determined the structure of the N-terminal domain of SidC, which has no structural homology to any protein. Sequence homology analysis revealed a potential canonical catalytic triad formed by Cys46, His444, and Asp446 on the surface of SidC. Unexpectedly, we found that SidC is an E3 ubiquitin ligase that uses the C-H-D triad to catalyze the formation of high-molecular-weight polyubiquitin chains through multiple ubiquitin lysine residues. A C46A mutation completely abolished the E3 ligase activity and the ability of the protein to recruit host ER proteins as well as polyubiquitin conjugates to the LCV. Thus, SidC represents a unique E3 ubiquitin ligase family important for phagosomal membrane remodeling by L. pneumophila.
authors.affiliation: Weill Institute for Cell and Molecular Biology and Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853;
authors.forename: FoSheng
authors.initials: F
authors.lastname: Hsu
authors.affiliation: Weill Institute for Cell and Molecular Biology and Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853;
authors.forename: Xi
authors.initials: X
authors.lastname: Luo
authors.affiliation: Department of Biological Sciences, Purdue University, West Lafayette, IN 47907; and.
authors.forename: Jiazhang
authors.initials: J
authors.lastname: Qiu
authors.affiliation: Weill Institute for Cell and Molecular Biology and Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853;
authors.forename: Yan-Bin
authors.initials: YB
authors.lastname: Teng
authors.affiliation: Department of Biochemistry and Molecular Biology, Medical School, The University of Texas Health Science Center at Houston, Houston, TX 77030.
authors.forename: Jianping
authors.initials: J
authors.lastname: Jin
authors.affiliation: Weill Institute for Cell and Molecular Biology and Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853;
authors.forename: Marcus B
authors.initials: MB
authors.lastname: Smolka
authors.affiliation: Department of Biological Sciences, Purdue University, West Lafayette, IN 47907; and ym253@cornell.edu luoz@purdue.edu.
authors.forename: Zhao-Qing
authors.initials: ZQ
authors.lastname: Luo
authors.affiliation: Weill Institute for Cell and Molecular Biology and Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853; ym253@cornell.edu luoz@purdue.edu.
authors.forename: Yuxin
authors.initials: Y
authors.lastname: Mao
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism*; D015415:Biomarkers / Q000378:metabolism; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D004023:Dictyostelium / Q000382:microbiology; D004721:Endoplasmic Reticulum; D057809:HEK293 Cells; D006801:Humans; D042541:Intracellular Space / Q000378:metabolism; D016952:Legionella pneumophila / Q000201:enzymology* / Q000502:physiology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010588:Phagosomes / Q000378:metabolism*; D017434:Protein Structure, Tertiary; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D054875:Ubiquitination; D014617:Vacuoles / Q000382:microbiology
chemical_list: D001426:Bacterial Proteins; D015415:Biomarkers; C534216:SidC protein, Legionella pneumophila; D044767:Ubiquitin-Protein Ligases
keywords: ER vesicle; membrane trafficking; pathogen infection; type IV secretion system; ubiquitination