title: NleG Type 3 effectors from enterohaemorrhagic Escherichia coli are U-Box E3 ubiquitin ligases.
abstract: NleG homologues constitute the largest family of Type 3 effectors delivered by pathogenic E. coli, with fourteen members in the enterohaemorrhagic (EHEC) O157:H7 strain alone. Identified recently as part of the non-LEE-encoded (Nle) effector set, this family remained uncharacterised and shared no sequence homology to other proteins including those of known function. The C-terminal domain of NleG2-3 (residues 90 to 191) is the most conserved region in NleG proteins and was solved by NMR. Structural analysis of this structure revealed the presence of a RING finger/U-box motif. Functional assays demonstrated that NleG2-3 as well as NleG5-1, NleG6-2 and NleG9' family members exhibited a strong autoubiquitination activity in vitro; a characteristic usually expressed by eukaryotic ubiquitin E3 ligases. When screened for activity against a panel of 30 human E2 enzymes, the NleG2-3 and NleG5-1 homologues showed an identical profile with only UBE2E2, UBE2E3 and UBE2D2 enzymes supporting NleG activity. Fluorescence polarization analysis yielded a binding affinity constant of 56+/-2 microM for the UBE2D2/NleG5-1 interaction, a value comparable with previous studies on E2/E3 affinities. The UBE2D2 interaction interface on NleG2-3 defined by NMR chemical shift perturbation and mutagenesis was shown to be generally similar to that characterised for human RING finger ubiquitin ligases. The alanine substitutions of UBE2D2 residues Arg5 and Lys63, critical for activation of eukaryotic E3 ligases, also significantly decreased both NleG binding and autoubiquitination activity. These results demonstrate that bacteria-encoded NleG effectors are E3 ubiquitin ligases analogous to RING finger and U-box enzymes in eukaryotes.
authors.affiliation: Division of Cancer Genomics and Proteomics, Ontario Cancer Institute, Toronto, Ontario, Canada.
authors.forename: Bin
authors.initials: B
authors.lastname: Wu
authors.forename: Tatiana
authors.initials: T
authors.lastname: Skarina
authors.forename: Adelinda
authors.initials: A
authors.lastname: Yee
authors.forename: Marie-Claude
authors.initials: MC
authors.lastname: Jobin
authors.forename: Rosa
authors.initials: R
authors.lastname: Dileo
authors.forename: Anthony
authors.initials: A
authors.lastname: Semesi
authors.forename: Christophe
authors.initials: C
authors.lastname: Fares
authors.forename: Alexander
authors.initials: A
authors.lastname: Lemak
authors.forename: Brian K
authors.initials: BK
authors.lastname: Coombes
authors.forename: Cheryl H
authors.initials: CH
authors.lastname: Arrowsmith
authors.forename: Alexander U
authors.initials: AU
authors.lastname: Singer
authors.forename: Alexei
authors.initials: A
authors.lastname: Savchenko
mesh_terms: D000595:Amino Acid Sequence; D054324:Enterohemorrhagic Escherichia coli / Q000201:enzymology* / Q000235:genetics / Q000254:growth & development; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation / Q000235:genetics; D019906:Nuclear Magnetic Resonance, Biomolecular; D011487:Protein Conformation; D054829:RING Finger Domains; D017386:Sequence Homology, Amino Acid; D044763:Ubiquitin-Conjugating Enzymes / Q000235:genetics / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D029968:Escherichia coli Proteins; C097309:UBE2D2 protein, human; D044763:Ubiquitin-Conjugating Enzymes; D044767:Ubiquitin-Protein Ligases