Identification of a common docking topology with substantial variation among different TCR-peptide-MHC complexes

Area of Science:

• Immunology
• Structural Biology
• Molecular Recognition

Background:

• The precise mechanism by which T-cell receptors (TCRs) bind to peptide-major histocompatibility complex (pMHC) ligands is crucial for adaptive immunity.
• Uncertainty exists regarding whether TCRs utilize conserved or variable docking strategies when interacting with pMHCs.

Purpose of the Study:

• To elucidate the structural basis of TCR-pMHC recognition by determining the crystal structure of a specific TCR-pMHC complex.
• To compare this structure with existing TCR-pMHC complex structures to identify commonalities and variations in docking modes.

Main Methods:

• X-ray crystallography was employed to determine the high-resolution structure of the N15 TCR complexed with its VSV8 peptide-H-2Kb MHC ligand.
• Comparative structural analysis was performed using previously determined structures of other TCR-pMHC complexes (2C TCR and A6 TCR).

Main Results:

• A conserved docking mode was identified where the TCR Valpha domain binds over the MHC alpha2 helix and the Vbeta domain binds over the MHC alpha1 helix.
• Complementarity-determining regions (CDRs) 1 and 3 of the TCR engage primarily with the peptide, while CDR2 loops interact mainly with the MHC molecule.
• Significant variations in TCR orientation, described as 'twist,' 'tilt,' and 'shift,' were observed, indicating fine-tuning of the interaction.

Conclusions:

• TCRs employ a common docking framework for pMHC recognition across different specificities and species.
• The observed variations in TCR orientation allow for precise modulation of the binding interaction with the peptide-MHC ligand.