title: Identification of UBact, a ubiquitin-like protein, along with other homologous components of a conjugation system and the proteasome in different gram-negative bacteria.
abstract: Systems analogous to the eukaryotic ubiquitin-proteasome system have been previously identified in Archaea, and Actinobacteria (gram-positive), but not in gram-negative bacteria. Here, we report the bioinformatic identification of a novel prokaryotic ubiquitin-like protein, which we name UBact. The phyletic distribution of UBact covers at least five gram-negative bacterial phyla, including Nitrospirae, Armatimonadetes, Verrucomicroba, Nitrospinae, and Planctomycetes. Additionally, it was identified in seven candidate (uncultured) phyla and one Archaeon. UBact might have been overlooked because only few species in the phyla where it is found have been sequenced. In most of the species where we identified UBact, its neighbors in the genome code for proteins homologous to those involved in conjugation and/or degradation of Pup and Pup-tagged substrates. Among them are PafA-, Dop-, Mpa- and proteasome-homologous proteins. This gene association as well as UBact's size and conserved C-terminal G[E/Q] motif, strongly suggest that UBact is used as a conjugatable tag for degradation. With regard to its C-terminus, UBact differs from ubiquitin and most ubiquitin-like proteins (including the mycobacterial Pup) in that it lacks the characteristic C-terminal di-glycine motif, and it usually ends with the sequence R[T/S]G[E/Q]. The phyla that contain UBact are thought to have diverged over 3000 million years ago, indicating that either this ubiquitin-like conjugation system evolved early in evolution or that its occurrence in distant gram-negative phyla is due to multiple instances of horizontal gene transfer.
authors.affiliation: The Technion Integrated Cancer Center (TICC), The Rappaport Faculty of Medicine and Research Institute, Technion-Israel Institute of Technology, Haifa 31096, Israel.
authors.forename: Gilad
authors.initials: G
authors.lastname: Lehmann
authors.affiliation: The Technion Integrated Cancer Center (TICC), The Rappaport Faculty of Medicine and Research Institute, Technion-Israel Institute of Technology, Haifa 31096, Israel.
authors.forename: Ronald G
authors.initials: RG
authors.lastname: Udasin
authors.affiliation: The Technion Integrated Cancer Center (TICC), The Rappaport Faculty of Medicine and Research Institute, Technion-Israel Institute of Technology, Haifa 31096, Israel.
authors.forename: Ido
authors.initials: I
authors.lastname: Livneh
authors.affiliation: The Technion Integrated Cancer Center (TICC), The Rappaport Faculty of Medicine and Research Institute, Technion-Israel Institute of Technology, Haifa 31096, Israel. Electronic address: aaroncie@tx.technion.ac.il.
authors.forename: Aaron
authors.initials: A
authors.lastname: Ciechanover
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D019295:Computational Biology; D017124:Conserved Sequence; D019143:Evolution, Molecular; D006090:Gram-Negative Bacteria / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D010802:Phylogeny; D046988:Proteasome Endopeptidase Complex / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D014452:Ubiquitins / Q000235:genetics / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D014452:Ubiquitins; D046988:Proteasome Endopeptidase Complex
keywords: Bacteria; Proteasome; Pup; UBact; Ubiquitin