Peptide binding inhibits aggregation of soluble MHC class II in solution

Area of Science:

• Immunology
• Molecular Biology
• Protein Biochemistry

Background:

• Major histocompatability complex (MHC) class II molecules bind antigenic peptides.
• Peptide binding induces structural changes in MHC class II molecules.
• Previous studies suggest a link between MHC class II structure and peptide association.

Purpose of the Study:

• To investigate the structural transition of aggregated MHC class II molecules upon high-affinity peptide binding.
• To demonstrate the conversion of aggregated human HLA-DR2 to stable heterodimers using myelin basic protein (MBP) peptide.
• To assess the biological activity of peptide-bound MHC class II heterodimers.

Main Methods:

• Purification of human HLA-DR2 and separation of aggregated (high molecular weight; HMW) from heterodimeric (low molecular weight; LMW) forms.
• Incubation of aggregated DR2 with high-affinity MBP(83-102)Y83 peptide under varying conditions (pH, temperature, reducing agent, peptide concentration).
• Assessment of biological activity using gamma-interferon production by T cells.

Main Results:

• Stable binding of high-affinity antigenic peptide induced aggregated MHC class II to transition into stable heterodimers.
• Aggregated HMW DR2 was converted to stable dimers upon incubation with MBP(83-102)Y83 peptide under optimized conditions.
• The transformed, peptide-bound heterodimers were biologically active, inducing gamma-interferon production in T cells.

Conclusions:

• MHC class II molecules may exist in an aggregated state in solution in the absence of bound peptide.
• High-affinity antigenic peptides can convert aggregated MHC class II molecules into stable, biologically active heterodimers.
• This transition mechanism is critical for the functional presentation of antigens by MHC class II molecules.