Peptide-induced conformational changes in class I molecules. Direct detection by flow cytometry

Area of Science:

• Immunology
• Structural Biology
• Molecular Interactions

Background:

• T cell activation relies on interactions between the T cell receptor (TCR), peptide, and MHC class I molecules.
• Previous studies suggest peptide modifications can influence T cell responses, hinting at indirect effects within the peptide-MHC complex.

Purpose of the Study:

• To investigate the conformational changes in mouse MHC class I molecule Kb when bound to ovalbumin peptide and its analogues.
• To determine if alterations at peptide position 2 (P2) affect MHC conformation and subsequent T cell stimulation.

Main Methods:

• Utilized monoclonal antibodies (mAbs) to probe the conformation of the alpha 1 and alpha 2 domains of the Kb molecule.
• Analyzed crystallographic data of Kb bound to ovalbumin peptide and 19 analogues differing at P2.
• Correlated conformational changes with T cell stimulation data.

Main Results:

• Substitution of peptide residue at P2, which is buried within the antigen-binding cleft, induced measurable conformational changes in the MHC class I molecule.
• These conformational changes directly correlated with the ability of the peptide-MHC complex to stimulate T cells.
• Side chains at P2 are not directly accessible to the TCR.

Conclusions:

• Peptide binding to MHC class I can induce indirect conformational effects on the MHC molecule.
• T cell activation can occur through direct TCR-MHC or TCR-peptide interactions, as well as indirectly via TCR recognition of MHC conformational changes induced by the peptide.
• This provides a new model for understanding the multifaceted nature of T cell activation by peptide-MHC complexes.