Peptide SQY

The recognition by T-cell antigen receptors (TCR) of antigenic peptides (p) bound to major histocompatibility complex (MHC)-encoded molecules is the basis of adaptive immune responses. During intrathymic differentiation, the genes encoding the variable (V) domain of the TCRα- and β-chains are assembled by site-specific DNA recombination reactions that result in the random recombination of V, diversity (D), and joining (J) gene segments. It has been argued that each clonally distributed TCR needs to cross-react with structurally distinct pMHC ligands. This property, called TCR degeneracy, is thought to permit the recognition by the whole TCR repertoire of a universe of potential antigenic peptides estimated to be much larger than the number of T-cell clones contained in an individual at a given moment. To differentiate in the thymus and, once mature, to achieve maximal sensitivity upon recognition of peptides of foreign origin, T cells also need to recognize, with low affinity, MHC molecules bearing peptides derived from self-proteins. Therefore, binding degeneracy constitutes an important TCR property.