Mutagenesis of Beryllium-Specific TCRs Suggests an Unusual Binding Topology for Antigen Recognition

Unconventional Ags, such as metals, stimulate T cells in a very specific manner. To delineate the binding landscape for metal-specific T cell recognition, alanine screens were performed on a set of Be-specific TCRs derived from the lung of a chronic beryllium disease patient. These TCRs are HLA-DP2-restricted and express nearly identical TCR V beta 5.1 chains coupled with different TCR alpha-chains. Site-specific mutagenesis of all amino acids comprising the CDRs of the TCRA and TCRB genes showed a dominant role for V beta 5.1 residues in Be recognition, with little contribution from the TCR alpha-chain. Solvent-exposed residues along the alpha-helices of the HLA-DP2 alpha- and beta-chains were also mutated to alanine. Two beta-chain residues, located near the proposed Be binding site of HLA-DP2, played a dominant role in T cell recognition with no contribution from the HLA-DP2 alpha-chain. These findings suggest that Be-specific T cells recognize Ag using an unconventional binding topology, with the majority of interactions contributed by TCR V beta 5.1 residues and the HLA-DP2 beta 1-chain. Thus, unusual docking topologies are not exclusively used by autoreactive T cells, but also for the recognition of unconventional metal Ags, such as Be. The Journal of Immunology, 2011, 187: 3694-3703.