Peptide variants reveal how antibodies recognize major histocompatibility complex class I

Area of Science:

• Immunology
• Molecular Biology
• Structural Biology

Background:

• The T cell receptor (TcR) on CD8+ T lymphocytes recognizes a peptide-MHC complex.
• Major histocompatibility complex (MHC) heavy chains, beta 2-microglobulin (beta 2M), and peptides form the recognized complex.
• Antibodies recognizing the Kb MHC complex are known to be sensitive to the bound peptide.

Purpose of the Study:

• To investigate the conformational changes in MHC heavy chains induced by bound peptides.
• To determine the extent to which different peptides bound to the Kb MHC complex influence antibody recognition.
• To differentiate between steric hindrance and conformational changes as mechanisms for peptide-MHC-antibody interactions.

Main Methods:

• Utilized eight Kb-specific allo-antibodies to analyze peptide binding.
• Generated and tested 128 single-amino acid variants of an ovalbumin-derived Kb-binding peptide.
• Assessed the impact of peptide variants on antibody binding to the Kb MHC complex.

Main Results:

• Seven of the eight Kb-specific antibodies tested showed peptide sensitivity.
• For most antibodies, bulky, solvent-exposed side chains on peptide variants inhibited binding, suggesting steric hindrance.
• Two antibodies (100.30 and 34.4.20) were affected by buried peptide residues, indicating recognition of altered peptide/MHC conformations.

Conclusions:

• Peptide composition significantly influences antibody recognition of the Kb MHC complex.
• Steric hindrance by solvent-exposed peptide residues is the primary mechanism for most Kb-specific antibodies.
• A subset of antibodies recognizes conformational changes in the peptide/MHC complex induced by specific peptide residues.