posters 5th Asia-Pacific NMR Symposium 2013

Mapping subunit organisation within the T cell receptor (TCR)-CD3 complex (#154)

Logesvaran Krshnan 1 2 , Melissa Call 1 2 , Matthew Call 1 2
  1. Structural Biology Division, Walter and Eliza Hall Institute of Medical Research, Parkville, VIC, Australia
  2. Department of Medical Biology, The University of Melbourne, Parkville, VIC, Australia

T cell receptor (TCR) activation is a defining event in adaptive immunity. Yet almost 30 years after the discovery of its molecular components, the mechanism of TCR “triggering” is still unknown. This is largely due to the complexity of the receptor and a lack of structural information on the intact complex. In order to form a functional receptor, the ligand-sensing TCRαβ heterodimer must assemble with the CD3γε, CD3δε and ζζ signal-transducing modules in the endoplasmic reticulum. The spatial arrangement of these eight subunits within an intact complex is not known, but the best-characterised TCR-CD3 interactions are specific polar contacts within their transmembrane (TM) domains that are critical for assembly and surface expression. To elucidate the architecture of the TCR-CD3 complex, I have designed an in vitro translation-based disulphide scanning approach to map further points of contact between TCR and CD3 TM domains in the context of fully assembled complex. My data indicate that TCRα and β TM domains are closely associated and identify several contacts within this previously unknown interface. These observations are guiding my solution NMR-based efforts to determine a detailed structure of the TCRαβ TM domain complex. I have successfully expressed and purified TM domain constructs of TCRα and TCRβ. Reconstitution of individual peptides in lyso-lipid micelles yields high-quality 2D 15N-Heteronuclear Single Quantum Correlation (HSQC) spectra and backbone assignments are underway using a standard suite of transverse-relaxation-optimised (TROSY) triple-resonance experiments. I am also developing a protocol to produce stable, stoichiometric TCRαβ TM complexes for structure determination by taking advantage of the natural intermolecular disulphide bond in the extracellular juxtamembrane domain known as the “connecting peptide”. Elucidating the spatial arrangement of TCR-CD3 complex subunits will provide an instructive platform to understand how these components cooperate to transmit the crucial signals that activate T cells.