Polymorphism at position 97 in MHC class I molecules affects peptide specificity, cell surface stability, and...

Area of Science:

• Immunology
• Molecular Biology
• Protein Chemistry

Background:

• Mouse MHC class I alleles L(d) and L(q) exhibit high sequence identity but distinct cell surface properties.
• L(q) shows stronger beta2-microglobulin (beta2m) association, higher expression, and longer half-life than L(d).

Purpose of the Study:

• To elucidate the molecular basis for the phenotypic differences between L(d) and L(q) MHC class I alleles.
• To identify specific amino acid residues responsible for variations in beta2m association and cell surface stability.

Main Methods:

• Construction and characterization of chimeric L(d)-L(q) alpha2 domains.
• Site-directed mutagenesis to analyze the role of residue 97 (Trp in L(d), Arg in L(q)).
• Analysis of beta2m association, cell surface expression, half-life, and peptide binding affinity.

Main Results:

• Residue 97 (L(d)Trp vs. L(q)Arg) is critical for differential beta2m association.
• The L(d)W97R mutation enhances cell surface half-life and reduces open forms, similar to L(q).
• Both L(d)W97R and L(q) exhibit reduced binding affinity for a specific peptide compared to L(d).

Conclusions:

• Substitution at residue 97 alters the peptide binding cleft, affecting endogenous peptide binding and enhancing cell surface stability.
• Residue 97 plays a key role in L(d) function within alternative MHC class I antigen presentation pathways.
• The findings provide insights into the structure-function relationships of MHC class I molecules.