Poster Presentation The 44th Lorne Conference on Protein Structure and Function 2019

Investigating mechanisms of T cell receptor activation (#243)

Nick Chandler 1 2
  1. Walter and Eliza Hall Institute of medical research, Parkville, VIC, Australia
  2. Department of Medical Biology, University of Melbourne, Parkville, VIC, Australia

The T Cell Receptor (TCR) is an octameric receptor complex found on the surface of T cells responsible for binding and signalling in response to peptide antigens. The TCR octamer consists of four dimers, the ligand binding TCRαβ chains which associate with the CD3 signalling sub-units (CD3δε, CD3γε and CD3ζζ). The assembly of these sub-units is governed by a series interactions between basic and acidic residues on the transmembrane domains of the TCRαβ and CD3 sub-units, respectively. Additionally, our lab has identified a conserved interface between the TCRαβ TM subunits, shown to be vital for TCR complex assembly and stability(1, 2).

 

In addition to their role in complex assembly, these domains are thought to play an important role in TCR signal transduction. Specifically, two recent models propose that ligand-induced rearrangements of the TM helices could permit signal transduction from the ligand-binding TCRαβ to the CD3 signalling subunits(3, 4). Whether the conserved TCRαβ interface we identified experiences structural rearrangement for signalling to occur is currently unknown. To answer this question, we have utilized two protein engineering approaches aiming to restrict the conformational freedom of this interface. These involve the use of leucine zipper fusions to tether the TCRαβ TM together from the intracellular side and the introduction of an engineered disulfide bond to lock them together from the extracellular side. Both of these approaches are predicted to maintain the TCRαβ TM interface present in the inactive receptor and I have shown that both are compatible with receptor assembly and surface expression. Ongoing functional analyses promise to provide valuable insights into the structural requirements for signalling through the TCR.

 

 

  1. 1. L. Krshnan, S. Park, W. Im, M. J. Call, M. E. Call, A conserved alpha beta transmembrane interface forms the core of a compact T-cell receptor-CD3 structure within the membrane. P Natl Acad Sci USA 113, E6649-E6658 (2016).
  2. 2. S. Park, L. Krshnan, M. J. Call, M. E. Call, W. Im, Structural Conservation and Effects of Alterations in T Cell Receptor Transmembrane Interfaces. Biophys J 114, 1030-1035 (2018).
  3. 3. K. N. Brazin et al., The T Cell Antigen Receptor alpha Transmembrane Domain Coordinates Triggering through Regulation of Bilayer Immersion and CD3 Subunit Associations. Immunity 49, 829-+ (2018).
  4. 4. M. S. Lee et al., A Mechanical Switch Couples T Cell Receptor Triggering to the Cytoplasmic Juxtamembrane Regions of CD3zetazeta. Immunity 43, 227-239 (2015).