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Membrane interactions influence the peptide binding behavior of DR1
M A Sherman1, H A Runnels, J C Moore
1Department of Pathology, Emory University School of Medicine, Atlanta, Georgia 30322.
Abstract:
We analyzed the binding of an influenza matrix protein-derived peptide, MAT(17-31), to cell surface and purified DR1. The pH dependence of peptide binding was dramatically influenced by the membrane environment. Cell surface binding was enhanced at low pH, with little or no binding detected at neutral pH and optimal binding at pH 4. By contrast, hydrogen ion concentration had minimal effect on peptide binding to purified DR1. Exposure to low pH in the absence of peptide did not affect the peptide binding capacity of cell-associated DR1. Purified DR1 was stable at low pH, excluding the possibility that enhanced binding was offset by a competing denaturation event at low pH. The striking effect of pH on peptide binding characteristic of cell surface DR1 was recovered after reconstitution of purified DR1 in B cell membranes by detergent dialysis. This behavior was partially recovered by reconstitution of full-length, but not truncated DR1 in vesicles containing purified lipid. Our results demonstrate that interactions involving membrane components influence the peptide-binding behavior of DR1.
Insights
Membrane environment significantly impacts influenza matrix peptide binding to DR1. Cell surface DR1 binding is pH-dependent, unlike purified DR1, highlighting crucial membrane interactions.
Area of Science:
- Immunology
- Biochemistry
- Molecular Biology
Background:
- The binding of peptides to MHC class II molecules like DR1 is critical for immune response.
- Understanding the factors influencing this binding, particularly in a cellular context, is essential for dissecting immune recognition mechanisms.
Purpose of the Study:
- To investigate the influence of the membrane environment on the pH-dependent binding of an influenza matrix peptide (MAT(17-31)) to DR1.
- To determine whether membrane components modulate DR1's peptide-binding characteristics.
Main Methods:
- Analysis of MAT(17-31) peptide binding to cell surface and purified DR1 across a range of pH values.
- Assessing the stability of purified DR1 at low pH.
- Reconstitution of purified DR1 into B cell membranes and lipid vesicles to evaluate the role of membrane components.
Main Results:
- Cell surface DR1 exhibited pH-dependent MAT(17-31) binding, with enhanced binding at low pH (optimal at pH 4) and minimal binding at neutral pH.
- Purified DR1 showed minimal pH-dependent binding, indicating the membrane environment is key.
- Reconstitution of DR1 into B cell membranes restored the pH-dependent binding behavior, with partial recovery in lipid vesicles containing full-length DR1.
Conclusions:
- Membrane components play a crucial role in modulating the pH-dependent peptide-binding properties of DR1.
- These findings suggest that the cellular membrane environment influences antigen presentation by MHC class II molecules.