Oral Presentation The 45th Lorne Conference on Protein Structure and Function 2020

TIR-domain-assembly formation in Toll-like receptor signaling pathways (#29)

Jeffrey D Nanson 1 2 , Thomas Ve 1 3 , Joseph Box 1 , Andrew Hedger 1 , Lou Brillault 1 2 , Edward H Egelman 4 , Michael J Landsberg 1 2 , Bostjan Kobe 1 2
  1. School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, QLD, Australia
  2. Institute for Molecular Bioscience, The University of Queensland, Brisbane, QLD, Australia
  3. Institute for Glycomics, Griffith University, Southport, QLD, Australia
  4. Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, Virginia, USA

Toll-like receptors (TLRs) detect pathogen- and endogenous danger-associated molecules, initiating innate immune responses that lead to the production of pro-inflammatory cytokines. TLR signal transduction occurs through homotypic interactions between the TLR Toll/interleukin-1 receptor (TIR) domain and TIR domains of the adaptor proteins MAL, MyD88, TRIF, and TRAM. Recruitment of these adaptors via TIR:TIR interactions orchestrates the recruitment of downstream effector enzymes, leading to immune responses1.

The MAL TIR domain (MALTIR) has been shown to self-assemble into filaments in vitro, form co-filaments with the TLR4 TIR domain (TLR4TIR), and induce the formation of MyD88 assemblies. The cryo-EM structure of the MALTIR filament reveals a proto-filament consisting of two parallel strands of TIR domains in a head-to-tail assembly2. To further elucidate the structural basis of TLR signaling and TIR:TIR domain interactions, we sought to determine the structure of TLR4TIR:MALTIR filaments using cryo-EM. Cryo-EM of TLR4TIR:MALTIR filaments revealed two filament morphologies, with reconstructions of the two TLR4TIR:MALTIR filaments resolved to resolutions of 3.8Å and 4.4Å. Modelling of TLR4TIR and MALTIR subunits within the TLR4TIR:MALTIR filaments indicates MALTIR forms proto-filaments similar to those observed in the structure of the MALTIR filament. Furthermore, TLR4TIR subunits form a single strand sandwiched between MALTIR proto-filaments. The interactions within the TLR4TIR:MALTIR filaments may reflect the biological assemblies and the molecular mechanisms of TIR:TIR interactions between TIR domains in TLR signaling pathways.

  1. Nanson, J. D., Kobe, B., & Ve, T. (2019). Death, TIR, and RHIM: Self‐assembling domains involved in innate immunity and cell‐death signaling. Journal of leukocyte biology, 105(2), 363-375.
  2. Ve, T., et al. (2017). Structural basis of TIR-domain-assembly formation in MAL-and MyD88-dependent TLR4 signaling. Nature structural & molecular biology, 24(9), 743.