MHC class II-associated invariant chain, trimerisation (IPR011988)

Short name: MHC_II-assoc_invariant_trimer

Overlapping homologous superfamilies

Domain relationships



Newly synthesized MHCII proteins associate with a chaperone protein called the invariant chain (Ii) and form a nonameric complex (alpha3beta3Ii3) in the endoplasmic reticulum [PMID: 1956401]. Ii plays a critical role in the assembly of the MHC, as well as in MHC II antigen processing by stabilising peptide-free class II alpha/beta heterodimers in a complex soon after their synthesis and directing transport of the complex from the endoplasmic reticulum to compartments where peptide loading of class II takes place [PMID: 16337363]. In antigen-presenting cells (APCs), loading of MHC II molecules with peptides is regulated by Ii, which blocks MHC II antigen-binding sites in pre-endosomal compartments [PMID: 16181341]. Several molecules then act upon MHC II molecules in endosomes to facilitate peptide loading: Ii-degrading proteases, the peptide exchange factor, human leukocyte antigen-DM (HLA-DM), and its modulator, HLA-DO (DO).

Ii first assembles into a trimer and then associates with three class II alpha/beta MHC heterodimers. This entry represents the trimerisation domain of Ii. Its structure has been determined by NMR [PMID: 9843486].

GO terms

Biological Process

GO:0019882 antigen processing and presentation

Molecular Function

GO:0042289 MHC class II protein binding

Cellular Component

GO:0016021 integral component of membrane

Contributing signatures

Signatures from InterPro member databases are used to construct an entry.