Abstract
The class II-associated in variant chain peptide (CLIP) region of invariant chain (Ii) is believed to play a critical role in the assembly and transport of MHC class II αβIi complexes through its interaction with the class II peptide-binding site. The role of the CLIP sequence was investigated by using mutant Ii molecules with altered affinity for the DR1 peptide- binding site. Both high- and low-affinity mutants were observed to efficiently assemble with DR1 and mediate transport to endosomal compartments in COS cell transfectants. Using N- and C-terminal truncations, a region adjacent to CLIP within Ii(103-118) was identified that can complement loss of affinity for the peptide-binding site in mediating efficient assembly of αβIi. A C-terminal fragment completely lacking the CLIP region, Ii(103- 216), was observed binding stably to class II molecules in immunoprecipitation studies and experiments with purified proteins. The Ii(103-118) region was required for this binding, which occurs through interactions outside of the αβ peptide-binding groove. We conclude that strong interactions involving Ii(103-118) and other regions of Ii cooperate in the assembly of functional αβIi under conditions where CLIP has little or no affinity for the class II peptide-binding site. Our results support the hypothesis that the CLIP sequence has evolved to avoid high-stability interactions with the peptide-binding sites of MHC class II molecules rather than as a promiscuous binder with moderate affinity for all class II molecules.
Original language | English (US) |
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Pages (from-to) | 1502-1509 |
Number of pages | 8 |
Journal | Journal of Immunology |
Volume | 162 |
Issue number | 3 |
State | Published - Feb 1 1999 |
ASJC Scopus subject areas
- Immunology and Allergy
- Immunology