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

Short name: MHC_II-assoc_invariant_trimer

Domain relationships



This entry represents the trimerisation domain of the MHC class II-associated invariant chain (Ii). 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).

The Invariant chain contains a single transmembrane domain. Ii first assembles into a trimer and then associates with three class II alpha/beta MHC heterodimers. Although the membrane-proximal region of the Ii luminal domain is structurally disordered, the C-terminal segment of the luminal domain is largely alpha-helical and contains a major interaction site for the Ii trimer [PMID: 9843486].

GO terms

Biological Process

GO:0019882 antigen processing and presentation
GO:0006955 immune response
GO:0006886 intracellular protein transport

Molecular Function

GO:0042289 MHC class II protein binding

Cellular Component

GO:0016020 membrane

Contributing signatures

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