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Intact proteins can bind to class II histocompatibility molecules with high affinity
H A Runnels1, D A Weber, J C Moore
1Department of Pathology and Laboratory Medicine, Emory University School of Medicine, Atlanta, Georgia 30322, U.S.A.
Molecular Immunology
|April 1, 1997
Summary
Intact protein antigens, like bovine ribonuclease (RNase) and horse myoglobin (Mb), can directly bind to purified class II histocompatibility molecules. This binding occurs within the peptide-binding groove and is enhanced by HLA-DM, supporting their role in immune responses.
Area of Science:
- Immunology
- Molecular Biology
- Protein Biochemistry
Background:
- Class II histocompatibility molecules present peptide antigens to T cells.
- The precise mechanism of initial antigen interaction with class II molecules is not fully understood.
- Investigating intact protein antigen binding is crucial for understanding antigen presentation pathways.
Purpose of the Study:
- To investigate the direct binding of intact protein antigens to purified class II histocompatibility molecules.
- To determine if intact proteins can bind via the peptide-binding groove.
- To explore the role of HLA-DM in the binding of intact protein antigens.
Main Methods:
- Inhibition assays using intact bovine ribonuclease (RNase) and horse myoglobin (Mb) to study peptide binding to DR1 and I-E(k) class II molecules.
- Direct visualization of I-E(k)-Mb complexes using SDS-PAGE.
- Binding experiments with biotin-labeled RNase and Mb to purified class II molecules.
- Assays to assess the effect of HLA-DM on biotin-RNase binding to DR1.
Main Results:
- Intact RNase and Mb potently inhibited peptide binding to purified class II molecules (DR1 and I-E(k)).
- Direct binding experiments confirmed high-affinity interaction of Mb and RNase with class II molecules through the peptide-binding groove, even without detergent.
- HLA-DM was shown to enhance the binding of intact RNase to DR1, suggesting a catalytic role.
- Complexes of I-E(k) and Mb were visualized on SDS-PAGE.
Conclusions:
- Intact, potentially partially unfolded, protein antigens can directly bind to purified class II histocompatibility molecules.
- This binding occurs with high affinity within the canonical peptide-binding groove.
- HLA-DM may play a role in facilitating the interaction between intact protein antigens and class II molecules.
- These findings support a model where intact proteins serve as initial ligands for class II molecules in antigen presentation.