BINDING OF PEPTIDES LACKING CONSENSUS ANCHOR RESIDUE ALTERS H-2L(D) SEROLOGIC RECOGNITION

CTL recognize class I MHC/peptide complexes on the surface of target c ells. Crystallographic and serologic data have indicated that peptide ligands can influence the conformation of class I molecules and hence T cell recognition. How the binding of peptides with disparate sequenc e motifs affects the conformation of distinct regions within a class I molecule remains unknown. A series of site-directed mutants of the mu rine class I molecule H-2L(d) was studied to address this question. Th ese mutants were generated by in vitro mutagenesis and used to map the serologic epitopes recognized by a panel of L(d)-reactive mAb. The in fluence of six different ligands on serologic recognition by these mAb was then examined. Of 12 mAb tested, only one, B22/249, was found to be significantly influenced by the bound peptide. Peptide discriminati on by B22/249 was observed at the cell surface and in immunoprecipitat es of L(d) after incubation with two of the six ligands. The two pepti des that caused suboptimal B22/249 recognition of L(d)/peptide lack a proline at position 2, which is present in the other four peptides and has previously been defined as an anchor residue for L(d) ligands. Th e epitope on L(d) detected by mAb B22/249 includes residues 63 to 70 o n the alpha1 domain helix. Two of these residues are in pocket B, whic h computer modeling predicts to be in contact with the second residue of L(d)-binding peptides. Therefore, these data imply that a mAb to a class I molecule can distinguish peptides with different motifs, possi bly reflecting peptide-dependent conformational changes in the class I molecule.