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

Investigating a common structural element in T- and B-cell antigen receptor transmembrane assembly (#225)

Samyuktha Ramesh 1 2 , Soohyung Park 3 , Wonpil Im 3 , Melissa J Call 1 2 , Matthew E Call 1 2
  1. Structural Biology Division, Walter and Eliza Hall Institute of Medical Research, Melbourne, Victoria, Australia
  2. Department of Medical Biology, University of Melbourne, Melbourne, Victoria, Australia
  3. Department of Biological Sciences and Bioengineering Program, Lehigh University, Bethlehem, Pennsylvania, USA

The antigen receptors on T and B cells, the T-cell receptor (TCR) and B-cell receptor (BCR), respectively, are the key initiators of adaptive immune responses and provide long-lasting protection against both internal and external threats to the body. Being single-spanning membrane protein complexes, structural characterisation by traditional biophysical techniques has proven challenging due to their hydrophobic transmembrane (TM) domains. As a result of this lack of high-resolution structures of intact TCR and BCR complexes, the molecular details of how these receptors assemble and function in the membrane remain poorly understood.

A recent study from our lab identified an interface between TCR αβ TM domains that is driven by highly conserved amino acids forming an inter-chain polar network and is a critical determinant of αβ TCR assembly and stability[1]. Sequence alignments and molecular dynamics simulations indicate that this structure is also present in the γδ- and pre-TCR complexes and in all vertebrate species that have conventional T cells[1, 2]. We now show that a similar structure likely exists in the homodimeric BCR ligand-sensing subunit, the membrane-bound immunoglobulin (mIg) protein. Preliminary modelling based on the TCR αβ TM structure supports this hypothesis, and the effects of targeted mutations in the mIg TM domains are consistent with a key role in mIg assembly with the BCR signalling module CD79AB. We are now using saturating mutagenesis, TM disulfide scanning, computational modelling and biophysical analyses to define the structural and functional role of this broadly conserved antigen receptor structural motif. We aim to better understand the evolution of antigen receptor structures and the structure-function relationship in these complex membrane protein assemblies.

  1. Krshnan, L., et al., A conserved alphabeta transmembrane interface forms the core of a compact T-cell receptor-CD3 structure within the membrane. Proc Natl Acad Sci U S A, 2016. 113(43): p. E6649-E6658.
  2. Park, S., et al., Structural Conservation and Effects of Alterations in T Cell Receptor Transmembrane Interfaces. Biophys J, 2018. 114(5): p. 1030-1035.