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Valkov E, Stamp A, DiMaio F, Baker D, Verstak B, Roversi P, Kellie S, Sweet MJ, Mansell A, Gay NJ, Martin JL, Kobe B. Crystal structure of Toll-like receptor adaptor MAL/TIRAP reveals the molecular basis for signal transduction and disease protection. Proc Natl Acad Sci U S A 2011; 108:14879-84. [PMID: 21873236 PMCID: PMC3169156 DOI: 10.1073/pnas.1104780108] [Citation(s) in RCA: 110] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Initiation of the innate immune response requires agonist recognition by pathogen-recognition receptors such as the Toll-like receptors (TLRs). Toll/interleukin-1 receptor (TIR) domain-containing adaptors are critical in orchestrating the signal transduction pathways after TLR and interleukin-1 receptor activation. Myeloid differentiation primary response gene 88 (MyD88) adaptor-like (MAL)/TIR domain-containing adaptor protein (TIRAP) is involved in bridging MyD88 to TLR2 and TLR4 in response to bacterial infection. Genetic studies have associated a number of unique single-nucleotide polymorphisms in MAL with protection against invasive microbial infection, but a molecular understanding has been hampered by a lack of structural information. The present study describes the crystal structure of MAL TIR domain. Significant structural differences exist in the overall fold of MAL compared with other TIR domain structures: A sequence motif comprising a β-strand in other TIR domains instead corresponds to a long loop, placing the functionally important "BB loop" proline motif in a unique surface position in MAL. The structure suggests possible dimerization and MyD88-interacting interfaces, and we confirm the key interface residues by coimmunoprecipitation using site-directed mutants. Jointly, our results provide a molecular and structural basis for the role of MAL in TLR signaling and disease protection.
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Affiliation(s)
- Eugene Valkov
- School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane, QLD 4072, Australia
| | - Anna Stamp
- School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane, QLD 4072, Australia
| | - Frank DiMaio
- Department of Biochemistry, University of Washington, Seattle, WA 98195
| | - David Baker
- Department of Biochemistry, University of Washington, Seattle, WA 98195
| | - Brett Verstak
- Centre for Innate Immunity and Infectious Diseases, Monash Institute of Medical Research, Monash University, Clayton, VIC 3168, Australia
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1GA, United Kingdom
| | - Pietro Roversi
- Sir William Dunn School of Pathology, University of Oxford, Oxford OX1 3RE, United Kingdom
| | - Stuart Kellie
- School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane, QLD 4072, Australia
- Australian Infectious Diseases Research Centre, University of Queensland, Brisbane, QLD 4072, Australia; and
| | - Matthew J. Sweet
- Australian Infectious Diseases Research Centre, University of Queensland, Brisbane, QLD 4072, Australia; and
- Institute for Molecular Bioscience, Queensland Bioscience Precinct, University of Queensland, Brisbane, QLD 4072, Australia
| | - Ashley Mansell
- Centre for Innate Immunity and Infectious Diseases, Monash Institute of Medical Research, Monash University, Clayton, VIC 3168, Australia
| | - Nicholas J. Gay
- Department of Biochemistry, University of Cambridge, Cambridge CB2 1GA, United Kingdom
| | - Jennifer L. Martin
- Australian Infectious Diseases Research Centre, University of Queensland, Brisbane, QLD 4072, Australia; and
- Institute for Molecular Bioscience, Queensland Bioscience Precinct, University of Queensland, Brisbane, QLD 4072, Australia
| | - Bostjan Kobe
- School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane, QLD 4072, Australia
- Australian Infectious Diseases Research Centre, University of Queensland, Brisbane, QLD 4072, Australia; and
- Institute for Molecular Bioscience, Queensland Bioscience Precinct, University of Queensland, Brisbane, QLD 4072, Australia
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Abstract
The experimental studies of Brucei group trypanosomes presented here demonstrate that the balance of host and parasite factors, especially IFN-γ GPI-sVSG respectively, and the timing of cellular exposure to them, dictate the predominant MP and DC activation profiles present at any given time during infection and within specific tissues. The timing of changes in innate immune cell functions following infection consistently support the conclusion that the key events controlling host resistance occur within a short time following initial exposure to the parasite GPI substituents. Once the changes in MP and DC activities are initiated, there appears little that the host can do to reverse these changes and alter the final outcome of these regulatory events. Instead, despite the availability of multiple innate and adaptive immune mechanisms that can control parasites, there is an inability to control trypanosome numbers sufficiently to prevent the emergence and establishment of virulent trypanosomes that eventually kill the host. Overall it appears that trypanosomes have carefully orchestrated the host innate and adaptive immune response so that parasite survival and transmission, and alterations of host immunity, are to its ultimate benefit.
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