HLA-DR3 molecules can bind peptides carrying two alternative specific submotifs

Area of Science:

• Immunology
• Molecular Biology
• Biochemistry

Background:

• Three distinct peptide binding motifs for HLA-DR3 have been proposed, differing in C-terminal anchor residues.
• Previous models suggest a primary hydrophobic anchor at the N-terminus for HLA-DR3 binding.

Purpose of the Study:

• To investigate the structural requirements for peptide binding to HLA-DR3.
• To refine existing HLA-DR3 peptide binding motifs by examining anchor residue flexibility.
• To evaluate the predictive accuracy of a refined motif using Mycobacterium tuberculosis peptides.

Main Methods:

• Quantitative HLA-DR3-specific binding assays were performed.
• Sets of single substitution analogues of known DR3 binding peptides were synthesized and tested.
• The binding capacity of overlapping peptides from Mycobacterium tuberculosis 65-kDa heat shock protein was assessed.

Main Results:

• HLA-DR3 peptide binding requirements vary; weak or absent anchors at positions n or n+3 can be compensated by a strong, positively charged anchor at position n+5.
• This flexibility explains discrepancies in previously reported DR3-specific peptide binding motifs.
• A refined DR3 motif showed a strong correlation with peptide binding to purified HLA-DR3 molecules, particularly for Mycobacterium tuberculosis peptides.

Conclusions:

• The study refines the understanding of HLA-DR3 peptide binding motifs, highlighting the importance of anchor residue flexibility.
• The refined motif demonstrates improved predictive value for identifying DR3-binding peptides.
• These findings have implications for understanding immune responses and developing peptide-based therapeutics.