Murine T10 and T22 are highly related nonclassical major histocompatibility
complex (MHC) class Ib proteins that bind to certain gamma delta T cell re
ceptors (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-bi
nding sites can be inferred from functional mapping of T10 and T22 point mu
tants and allelic variants. Thus, T22 represents an unusual variant of the
MHC-like fold and indicates that gamma delta and alpha beta TCRs interact d
ifferently with their respective MHC ligands.