Self and foreign peptides interact with intact and disassembled MHC class II antigen HLA-DR via tryptophan pockets

摘要: The acid release of endogenous peptides from immunoaffinity-pure human major histocompatibility complex (MHC) class II proteins HLA-DR1 is accompanied by an 18% decrease in intrinsic tryptophan fluorescence. effect totally reversible upon readdition autologous peptide fraction. High-performance size-exclusion chromatographic (HPSEC) binding and studies with a nonfluorescent HLA-DR1-restricted influenza matrix IM(18-29) prove the fact that Trp residues HLA protein change their fluorescence intensities. Since far-UV circular dichroism spectra molecules before after release, DR1[NAT] DR1[REL], show very small differences, we can rule out breakdown secondary structural elements under conditions, although DR[REL] consists disassembled alpha- beta-subunits, as evidenced HPSEC. Quenching DR1[REL] using neutral quencher acrylamide results 20% increase total accessibility nine-residue population whereas quenching iodide yields only 5% increase. Both taken together tell us two residues, preferentially ones located apolar pockets, become accessible peptides. significantly smaller enhancement DR3[REL], exclusively lacking Trp-9(beta 1), missing tendency to reassemble influence compared suggest important role for position 9(beta 1). region around Trp-43(alpha 1) should be responsible alpha-subunits DR1 DR3, respectively, verified fluorometric HPSEC SDS-PAGE. Obviously, our findings are agreement hypothetical MHC model, whereafter besides Trp-61(beta constituents groove DR1. Extending homology I products, postulate existence three hydrophobic pockets site cited being juxtaposed contacting side chains HLA-peptide complexes. According deduced two-residue-contact model minimal consensus motif DR1-restricted antigens lying 14-16 A apart bound state peptide.