Crystal structure of a γδ T cell receptor ligand T22:: A truncated MHC-like fold

Murine T10 and T22 are highly related nonclassical major histocompatibility complex (MHC) class Ib proteins that bind to certain gamma delta T cell receptors (TCRs) in the absence of other components. The crystal structure of T22(b) at 3.1 angstroms reveals similarities to MHC class I molecules, but one side of the normal peptide-binding groove is severely truncated, which allows direct access to the beta-sheet floor. Potential gamma delta TCR-binding sites can be inferred from functional mapping of T10 and T22 point mutants and allelic variants. Thus, T22 represents an unusual variant of the MHC-like fold and indicates that gamma delta and alpha beta TCRs interact differently with their respective MHC ligands.