MHC class II protein complex

Definition

Target type: cellularcomponent

A transmembrane protein complex composed of an MHC class II alpha and MHC class II beta chain, and with or without a bound peptide or polysaccharide antigen. [GOC:add, GOC:jl, ISBN:0120781859, PMID:15928678]

The MHC class II protein complex is a multi-protein assembly found primarily on the surface of antigen-presenting cells (APCs), such as macrophages, dendritic cells, and B cells. It plays a crucial role in the adaptive immune response by presenting processed peptide antigens to CD4+ T lymphocytes. The cellular component of the MHC class II complex is composed of several key components:

- **MHC Class II α and β Chains:** These are the two transmembrane glycoproteins that form the core of the complex. They have a unique structure with an extracellular domain that binds antigenic peptides, a transmembrane domain that anchors the complex to the cell membrane, and a cytoplasmic tail that interacts with intracellular signaling molecules.

- **Invariant Chain (Ii):** This is a chaperone protein that associates with MHC class II molecules in the endoplasmic reticulum (ER). It prevents the binding of peptides to MHC class II in the ER and guides the complex to the endosomal compartments for peptide loading.

- **HLA-DM:** This is another transmembrane protein found in the endosomal compartment. HLA-DM facilitates the release of Ii and the loading of peptides onto MHC class II molecules.

- **MHC Class II-Associated Invariant Chain Peptides (CLIP):** These are short peptide fragments derived from the invariant chain that remain bound to MHC class II molecules in the ER. They act as placeholders for the actual antigenic peptides.

- **LMP2 and LMP7:** These are two proteases located in the proteasome, a large protein complex responsible for degrading intracellular proteins. They generate peptides that are optimal for binding to MHC class II molecules.

- **TAP1 and TAP2:** These are two transmembrane proteins located in the ER membrane. They transport peptides generated by the proteasome from the cytoplasm to the lumen of the ER, where they can bind to MHC class II molecules.

- **Other Associated Proteins:** Several other proteins may be associated with the MHC class II complex, including chaperones, transporters, and signaling molecules. These proteins contribute to the proper assembly, trafficking, and function of the complex.

The cellular component of the MHC class II protein complex is thus a dynamic and intricate assembly that plays a crucial role in the adaptive immune response. It allows APCs to display processed peptide antigens to CD4+ T lymphocytes, initiating the immune response against foreign pathogens.'
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Proteins (1)

Compounds (2)