Exploration of the P6/P7 region of the peptide-binding site of the human class II major histocompatability complex protein HLA-DR1.

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TitleExploration of the P6/P7 region of the peptide-binding site of the human class II major histocompatability complex protein HLA-DR1.
Publication TypeJournal Article
Year of Publication2003
AuthorsZavala-Ruiz, Z, Sundberg, EJ, Stone, JD, DeOliveira, DB, Chan, IC, Svendsen, J, Mariuzza, RA, Stern, LJ
JournalJ Biol Chem
Volume278
Issue45
Pagination44904-12
Date Published2003 Nov 7
ISSN0021-9258
KeywordsAlanine, Amino Acid Sequence, Binding Sites, Crystallization, HLA-DR1 Antigen, Humans, Hydrogen Bonding, Lymphocyte Activation, Methylation, Models, Molecular, Molecular Structure, Peptides, Protein Conformation, Protein Structure, Secondary, Sarcosine, Structure-Activity Relationship, T-Lymphocytes
Abstract

Crystal structures of the class II major histocompatibilty complex (MHC) protein, HLA-DR1, generally show a tight fit between MHC and bound peptide except in the P6/P7 region of the peptide-binding site. In this region, there is a shallow water-filled pocket underneath the peptide and between the pockets that accommodate the P6 and P7 side chains. We investigated the properties of this pocket with the idea of engineering substitutions into the corresponding region of peptide antigens to increase their binding affinity for HLA-DR1. We investigated d-amino acids and N-alkyl modifications at both the P6 and P7 positions of the peptide and found that binding of peptides to HLA-DR1 could be increased by incorporating an N-methyl substitution at position 7 of the peptide. The crystal structure of HLA-DR1 bound to a peptide containing a P7 N-methyl alanine was determined. The N-methyl group orients in the P6/P7 pocket, displacing one of the waters usually bound in this pocket. The structure shows that the substitution does not alter the conformation of the bound peptide, which adopts the usual polyproline type II helix. An antigenic peptide carrying the N-methyl modification is taken up by antigen-presenting cells and loaded onto endogenous class II MHC molecules for presentation, and the resultant MHC-peptide complexes activate antigen-specific T-cells. These results suggest a possible strategy for increasing the affinity of weakly immunogenic peptides that might be applicable to the development of vaccines and diagnostic reagents.

DOI10.1074/jbc.M307652200
Alternate JournalJ. Biol. Chem.
PubMed ID12952957
Grant ListF31-GM64859 / GM / NIGMS NIH HHS / United States
R01-AI369000 / AI / NIAID NIH HHS / United States
R01-AI38996 / AI / NIAID NIH HHS / United States