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Modulation of HLA-DQ binding properties by differences in class II dimer stability and pH-dependent peptide
Journal of Immunology (Baltimore, Md. : 1950)
|December 1, 1996
Summary
Human leukocyte antigen (HLA) class II molecules like HLA-DQ3.1 and HLA-DQ3.2 exhibit distinct pH-dependent peptide binding preferences. These differences, influenced by molecular structure and pH, impact autoimmune disease associations.
Area of Science:
- Immunology
- Molecular Biology
- Biochemistry
Background:
- Interactions between peptides and human leukocyte antigen (HLA) class II molecules are crucial for immune responses.
- Intracellular peptide loading occurs in endosomal compartments with varying pH levels.
- HLA-DQ alleles 3.1 and 3.2, despite structural similarities, are associated with different autoimmune disease susceptibilities.
Purpose of the Study:
- To compare the pH-dependent peptide binding profiles of HLA-DQ3.1 and HLA-DQ3.2.
- To investigate the influence of pH on the binding affinity of various peptides to these HLA-DQ alleles.
- To explore the role of molecular structure, specifically residue 57 polymorphism, in pH-dependent binding.
Main Methods:
- Comparative analysis of peptide binding to purified HLA-DQ3.1 and HLA-DQ3.2 molecules across a range of pH conditions.
- Assessment of intrinsic alphabeta dimer stability using partially denaturing gel electrophoresis after pH incubation.
- Evaluation of binding for a promiscuous peptide (34P3A) and allele-specific peptides.
Main Results:
- HLA-DQ3.2 demonstrated optimal peptide binding at a more acidic pH (around 5.5) compared to HLA-DQ3.1 (around 6.5).
- A polymorphism at residue 57 of the DQ molecule contributed to, but did not fully explain, the observed pH-dependent binding differences.
- HLA-DQ3.2 showed relative instability at neutral pH, supporting its preference for acidic conditions for peptide binding, unlike a class II-associated invariant chain peptide.
Conclusions:
- Intrinsic alphabeta dimer stability and pH optima for peptide binding are significant factors determining allelic differences in HLA-DQ binding profiles.
- The distinct pH-dependent binding characteristics of HLA-DQ3.1 and HLA-DQ3.2 may contribute to their differential associations with autoimmune diseases.
- Understanding these pH-driven interactions is vital for elucidating antigen presentation mechanisms in vivo.