TIR domain polymerisation of adaptor proteins in the MyD88-independent pathway

A Hedger1, T Ve1,2, M Landsberg1,3 and B Kobe1,3

  1. School of Chemistry and Molecular Biosciences, and Australian Infectious Diseases Research Centre, University of Queensland, Brisbane, QLD 4072, Australia
  2. Institute for Glycomics, Griffith University, Southport, QLD 4222, Australia
  3. Institute for Molecular Bioscience, University of Queensland, Brisbane, QLD, 4072, Australia

Toll-like receptors (TLRs) are a family of membrane-bound pattern-recognition receptors (PRRs) that detect microbe-derived pathogen-associated molecular patterns (PAMPs) or host-derived damage-associated molecular patterns (DAMPs). Upon activation, TLRs undergo signall transduction that results in the release of transcription factors such as NF-κB, which induce expression of genes important for an innate immune response [1]. TLRs can signal through either the MyD88-dependant pathway, producing a higher-order protein complex known as the Myddosome; or alternatively through the MyD88-independent pathway, which is hypothesised to form a different higher-order complex. These adaptor proteins associate with each other via homotypic Toll-interleukin-1 receptor (TIR) interactions [2]. The TIR domains of the MyD88-dependent pathway MAL and MyD88 have already been characterised and we have observed that these proteins can form higher-order structures in vitro and in vivo (unpublished). To expand upon this work, we would like to look at higher-order assembly formation by the adaptor proteins TRAM and TRIF in the MyD88-independent pathway. TRAM has been purified and preliminary images of filaments have been taken using negative stain electron microscopy (EM). We would like to optimise TRAM polymerisation conditions and take images using cryo-EM for helical reconstruction. This would provide us a framework for understanding how TRAM undergoes polymerisation and possibly become an avenue for drug development.
References: 1. Ve, T., J. Gay, N., Mansell, A., Kobe, B. & Kellie, S. Adaptors in Toll-Like Receptor Signaling and their Potential as Therapeutic Targets. Current Drug Targets 13, 1360-1374 (2012). 2.Ve, T., Williams, S. J. & Kobe, B. Structure and function of Toll/interleukin-1 receptor/resistance protein (TIR) domains. Apoptosis 20, 250-261 (2015).