title: Mechanism of bacterial interference with TLR4 signaling by Brucella Toll/interleukin-1 receptor domain-containing protein TcpB.
abstract: Upon activation of Toll-like receptors (TLRs), cytoplasmic Toll/interleukin-1 receptor (TIR) domains of the receptors undergo homo- or heterodimerization. This in turn leads to the recruitment of adaptor proteins, activation of transcription factors, and the secretion of pro-inflammatory cytokines. Recent studies have described the TIR domain-containing protein from Brucella melitensis, TcpB (BtpA/Btp1), to be involved in virulence and suppression of host innate immune responses. TcpB interferes with TLR4 and TLR2 signaling pathways by a mechanism that remains controversial. In this study, we show using co-immunoprecipitation analyses that TcpB interacts with MAL, MyD88, and TLR4 but interferes only with the MAL-TLR4 interaction. We present the crystal structure of the TcpB TIR domain, which reveals significant structural differences in the loop regions compared with other TIR domain structures. We demonstrate that TcpB forms a dimer in solution, and the crystal structure reveals the dimerization interface, which we validate by mutagenesis and biophysical studies. Our study advances the understanding of the molecular mechanisms of host immunosuppression by bacterial pathogens.
authors.affiliation: From the School of Chemistry and Molecular Biosciences.
authors.forename: Mohammed
authors.initials: M
authors.lastname: Alaidarous
authors.forename: Thomas
authors.initials: T
authors.lastname: Ve
authors.forename: Lachlan W
authors.initials: LW
authors.lastname: Casey
authors.forename: Eugene
authors.initials: E
authors.lastname: Valkov
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Ericsson
authors.forename: M Obayed
authors.initials: MO
authors.lastname: Ullah
authors.forename: Mark A
authors.initials: MA
authors.lastname: Schembri
authors.forename: Ashley
authors.initials: A
authors.lastname: Mansell
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Sweet
authors.forename: Bostjan
authors.initials: B
authors.lastname: Kobe
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001665:Binding Sites / Q000235:genetics; D017347:Brucella melitensis / Q000235:genetics / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D062806:Myelin and Lymphocyte-Associated Proteolipid Proteins / Q000235:genetics / Q000378:metabolism; D053594:Myeloid Differentiation Factor 88 / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D011487:Protein Conformation; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D017472:Receptors, Interleukin-1 / Q000378:metabolism; D053838:Scattering, Small Angle; D017386:Sequence Homology, Amino Acid; D015398:Signal Transduction; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000378:metabolism*; D037521:Virulence Factors / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D014961:X-Ray Diffraction
chemical_list: D001426:Bacterial Proteins; C569026:MAL protein, human; D062806:Myelin and Lymphocyte-Associated Proteolipid Proteins; D053594:Myeloid Differentiation Factor 88; D017472:Receptors, Interleukin-1; C495345:TLR4 protein, human; C587630:TcpB protein, Brucella melitensis; D051197:Toll-Like Receptor 4; D037521:Virulence Factors
keywords: Adaptor Proteins; Innate Immunity; Protein Structure; Toll IL-1 Receptor (TIR) Domain; Toll-like Receptors (TLR)