Invariant chain (Ii), a membrane glycoprotein, binds class II major histocompatibility complex (MHC) glycoproteins, probably via its class II- associated Ii peptide (CLIP) segment, and escorts them toward antigen- containing endosomal compartments. We find that a soluble, trimeric ectodomain of Ii expressed and purified from Escherichia colt blocks peptide binding to soluble HLA-DR1. Proteolysis indicates that Ii contains two structural domains. The C-terminal two-thirds forms an α-helical domain that trimerizes and interacts with empty HLA-DR1 molecules, augmenting rather than blocking peptide binding. The N-terminal one-third, which inhibits peptide binding, is proteolytically susceptible over its entire length. In the trimer, the N-terminal domains act independently with each CLIP segment exposed and free to bind an MHC class II molecule, while the C-terminal domains act as a trimeric unit.
|Original language||English (US)|
|Number of pages||5|
|Journal||Proceedings of the National Academy of Sciences of the United States of America|
|State||Published - Nov 21 1995|
- antigen processing
- major histocompatibility complex class II
ASJC Scopus subject areas