Interaction between HLA-DM and HLA-DR involves regions that undergo conformational changes at lysosomal pH

AUTOR(ES)

Ullrich, H. Joachim

FONTE

The National Academy of Sciences of the USA

RESUMO

Antigenic peptide loading of major histocompatibility complex class II molecules is enhanced by lysosomal pH and catalyzed by the HLA-DM molecule. The physical mechanism behind the catalytic activity of DM was investigated by using time-resolved fluorescence anisotropy (TRFA) and fluorescence binding studies with the dye 8-anilino-1-naphthalenesulfonic acid (ANS). We demonstrate that the conformations of both HLA-DM and HLA-DR3, irrespective of the composition of bound peptide, are pH sensitive. Both complexes reversibly expose more nonpolar regions upon protonation. Interaction of DM with DR shields these hydrophobic domains from the aqueous environment, leading to stabilization of the DM and DR conformations. At lysosomal pH, the uncovering of additional hydrophobic patches leads to a more extensive DM–DR association. We propose that DM catalyzes class II peptide loading by stabilizing the low-pH conformation of DR, favoring peptide exchange. The DM–DR association involves a larger hydrophobic surface area with DR/class II-associated invariant chain peptides (CLIP) than with stable DR/peptide complexes, explaining the preferred association of DM with the former. The data support a release mechanism of DM from the DM–DR complex through reduction of the interactive surface, upon binding of class II molecules with antigenic peptide or upon neutralization of the DM–DR complex at the cell surface.

Documentos Relacionados

• Kinetic analysis of peptide loading onto HLA-DR molecules mediated by HLA-DM.
• In the absence of the invariant chain, HLA-DR molecules display a distinct array of peptides which is influenced by the presence or absence of HLA-DM
• HLA-DO is a lysosomal resident which requires association with HLA-DM for efficient intracellular transport.
• HLA-DR expression and soluble HLA-DR levels in septic patients after trauma.
• The kinetic basis of peptide exchange catalysis by HLA-DM