The high-resolution x-ray crystal structures of the murine major
histocompatibility complex (MHC) class II molecule, I-E(k), occupied by either
of two antigenic peptides were determined. They reveal the structural basis for
the I-E(k) peptide binding motif and suggest general principles for additional
alleles. A buried cluster of acidic amino acids in the binding groove predicted
to be conserved among all murine I-E and human DR MHC class II molecules
suggests how pH may influence MHC binding or exchange of peptides. These
structures also complement mutational studies on the importance of individual
peptide residues to T cell receptor recognition.
