title: Ubiquitination independent of E1 and E2 enzymes by bacterial effectors.
abstract: Signalling by ubiquitination regulates virtually every cellular process in eukaryotes. Covalent attachment of ubiquitin to a substrate is catalysed by the E1, E2 and E3 three-enzyme cascade, which links the carboxy terminus of ubiquitin to the ε-amino group of, in most cases, a lysine of the substrate via an isopeptide bond. Given the essential roles of ubiquitination in the regulation of the immune system, it is not surprising that the ubiquitination network is a common target for diverse infectious agents. For example, many bacterial pathogens exploit ubiquitin signalling using virulence factors that function as E3 ligases, deubiquitinases or as enzymes that directly attack ubiquitin. The bacterial pathogen Legionella pneumophila utilizes approximately 300 effectors that modulate diverse host processes to create a permissive niche for its replication in phagocytes. Here we demonstrate that members of the SidE effector family of L. pneumophila ubiquitinate multiple Rab small GTPases associated with the endoplasmic reticulum. Moreover, we show that these proteins are capable of catalysing ubiquitination without the need for the E1 and E2 enzymes. A putative mono-ADP-ribosyltransferase motif critical for the ubiquitination activity is also essential for the role of the SidE family in intracellular bacterial replication in a protozoan host. The E1/E2-independent ubiquitination catalysed by these enzymes is energized by nicotinamide adenine dinucleotide, which activates ubiquitin by the formation of ADP-ribosylated ubiquitin. These results establish that ubiquitination can be catalysed by a single enzyme, the activity of which does not require ATP.
authors.affiliation: Purdue Institute for Inflammation, Immunology and Infectious Disease and Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, USA.
authors.forename: Jiazhang
authors.initials: J
authors.lastname: Qiu
authors.affiliation: Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, USA.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Sheedlo
authors.affiliation: Institute of Analytical Chemistry and Synthetic and Functional Biomolecules Center, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China.
authors.forename: Kaiwen
authors.initials: K
authors.lastname: Yu
authors.affiliation: Purdue Institute for Inflammation, Immunology and Infectious Disease and Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, USA.
authors.forename: Yunhao
authors.initials: Y
authors.lastname: Tan
authors.affiliation: Biological Science Division, Pacific Northwest National Laboratory, Richland, Washington 99352, USA.
authors.forename: Ernesto S
authors.initials: ES
authors.lastname: Nakayasu
authors.affiliation: Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, Indiana 47907, USA.
authors.forename: Chittaranjan
authors.initials: C
authors.lastname: Das
authors.affiliation: Institute of Analytical Chemistry and Synthetic and Functional Biomolecules Center, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China.
authors.forename: Xiaoyun
authors.initials: X
authors.lastname: Liu
authors.affiliation: Purdue Institute for Inflammation, Immunology and Infectious Disease and Department of Biological Sciences, Purdue University, West Lafayette, Indiana 47907, USA.
authors.forename: Zhao-Qing
authors.initials: ZQ
authors.lastname: Luo
mesh_terms: D036002:ADP Ribose Transferases / Q000737:chemistry / Q000378:metabolism; D000246:Adenosine Diphosphate Ribose / Q000378:metabolism; D000255:Adenosine Triphosphate; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D058491:Bacterial Load; D001426:Bacterial Proteins / Q000378:metabolism*; D055162:Biocatalysis; D004721:Endoplasmic Reticulum / Q000201:enzymology / Q000378:metabolism; D016952:Legionella pneumophila / Q000737:chemistry* / Q000166:cytology / Q000201:enzymology / Q000472:pathogenicity; D008565:Membrane Proteins / Q000378:metabolism; D008969:Molecular Sequence Data; D009243:NAD / Q000378:metabolism; D025801:Ubiquitin / Q000737:chemistry / Q000378:metabolism; D044764:Ubiquitin-Activating Enzymes; D044763:Ubiquitin-Conjugating Enzymes; D054875:Ubiquitination; D037521:Virulence Factors / Q000378:metabolism; D020691:rab GTP-Binding Proteins / Q000737:chemistry / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D008565:Membrane Proteins; C503174:SdeA protein, Legionella pneumophila; D025801:Ubiquitin; D037521:Virulence Factors; D009243:NAD; D000246:Adenosine Diphosphate Ribose; D000255:Adenosine Triphosphate; D044763:Ubiquitin-Conjugating Enzymes; D036002:ADP Ribose Transferases; D020691:rab GTP-Binding Proteins; D044764:Ubiquitin-Activating Enzymes