Poster Presentation The 42nd Lorne Conference on Protein Structure and Function 2017

Structural basis of TIR-domain assembly formation in MyD88-dependent TLR4 signaling (#295)

Thomas Ve 1 , Parimala R Vajjhala 2 , Andrew Hedger 2 , Tristan Croll 3 , Frank DiMaio 4 , Shane Horsefield 2 , Xiong Yu 5 , Peter Lavrencic 2 , Garry P Morgan 6 , Ashley Mansell 7 , Mehdi Mobli 8 , Ailis O'Carrol 9 , Brieuc Chauvin 9 , Yann Gambin 9 , Emma Sierecki 9 , Michael J Landsberg 2 , Katryn J Stacey 2 , Edward H Egelman 5 , Bostjan Kobe 2
  1. Institute for Glycomics, Griffith University, Southport, QLD 4222, Australia
  2. School of Chemistry and Molecular Biosciences, University of Queensland, Brisbane, QLD 4072, Australia
  3. Cambridge Institute for Medical Research, University of Cambridge, Cambridge, United Kingdom
  4. Department of Biochemistry, University of Washington, Seattle, Washington, USA
  5. Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, VA 22908, USA
  6. Centre for Microscopy and Microanalysis, The University of Queensland, Brisbane, QLD 4072, Australia
  7. Centre for Innate Immunity and Infectious Diseases, Hudson Institute of Medical Research, Monash University, Melbourne, Victoria, Australia
  8. Centre for Advanced Imaging, University of Queensland, Brisbane, QLD, Australia
  9. EMBL Australia Node in Single Molecule Sciences, School of Medical Science, University of New South Wales, Sydney, NSW, Australia

MAL and MyD88 are signaling mediators for Toll-like receptors (TLRs) and form ternary complexes through TIR (Toll/interleukin-1 receptor [IL-1R]) domain interactions. We demonstrate that MAL can self-assemble or assemble with TLR4 into filaments, and that MAL induces formation of MyD88 assemblies. A 7 Å resolution cryo-electron microscopy structure of the MAL filament reveals a tube of 12 proto-filaments that consists of two parallel strands of TIR-domain subunits in a BB loop-mediated head-to-tail arrangement. Structure-guided mutagenesis, combined with cellular clustering assays, confirms that the proto-filament reproduces TIR:TIR interactions in TLR4 signaling. Our data suggest a signaling model that involves open-ended TLR4:MAL:MyD88 complexes, and explains the all-or-none TLR signaling responses. The conservation of residues involved in TIR:TIR interactions suggests analogous association modes in TLR/IL-1R signaling in general.