The mechanisms, how γδ TCRs interact with their cognate antigen remain poorly understood in spite of the rising interest in γδ T cells and their crucial role in the immune response. One of the main reasons for this gap in understanding is the limited number of identified γδ TCR / ligand pairs and the resulting small number of available structures of γδ TCRs in complex with their respective ligand.
In this project, we will structurally characterize the molecular interaction between γδ TCRs and their cognate ligand by X-ray crystallography using a specific Vγ3Vδ1+ TCR / HLA-DR (MHC class II) pair that was identified by the Prinz group in the previous funding period of FOR 2799. To this end, we will recombinantly express important amounts of soluble ectodomains from three TCR variants that are expected to bind the same ligand but with different binding affinity. We will also express important amounts of a soluble HLA-DR ectodomain in insect cells. Since HLA as MHC class II molecule requires interaction with a peptide for folding and stabilization, we will produce the latter as a fusion protein with various peptides to be presented. We will assemble complexes from the recombinant proteins, crystallize these complexes, determine the structure using X-ray crystallography and thereby identify the main determinants of this interaction. The expression of the HLA-DR in fusion with peptides also allows us to structurally characterize the role of the peptide using various HLA-DR / peptide combinations. This structural analysis will be complemented by a thorough biochemical analysis of this interaction that will provide detailed kinetic binding parameters of the TCR variants to a number of HLA /peptide combinations.
In summary, this project aims to considerably advance the understanding of how γδ TCRs interact with their cognate antigen. The scientific environment of the DFG Research Unit FOR 2799 “Receiving and Translating Signals via the γδ T Cell Receptor“ will provide optimal conditions for a sustainable exchange and we will share our complementary biochemical and structural biology expertise with all members of the consortium to potentially identify additional γδ TCR / ligand pairs.