Family

MHC class I alpha chain (IPR027648)

Short name: MHC_I_a

Family relationships

None.

Description

Major Histocompatibility Complex (MHC) glycoproteins are heterodimeric cell surface receptors that function to present antigen peptide fragments to T cells responsible for cell-mediated immune responses. MHC molecules can be subdivided into two groups on the basis of structure and function: class I molecules present intracellular antigen peptide fragments (~10 amino acids) on the surface of the host cells to cytotoxic T cells; class II molecules present exogenously derived antigenic peptides (~15 amino acids) to helper T cells. MHC class I and II molecules are assembled and loaded with their peptide ligands via different mechanisms. However, both present peptide fragments rather than entire proteins to T cells, and are required to mount an immune response.

Class I MHC glycoproteins are expressed on the surface of all somatic nucleated cells, with the exception of neurons. MHC class I receptors present peptide antigens that are synthesised in the cytoplasm, which includes self-peptides (presented for self-tolerance) as well as foreign peptides (such as viral proteins). These antigens are generated from degraded protein fragments that are transported to the endoplasmic reticulum by TAP proteins (transporter of antigenic peptides), where they can bind MHC I molecules, before being transported to the cell surface via the Golgi apparatus [PMID: 9485452, PMID: 15526153]. MHC class I receptors display antigens for recognition by cytotoxic T cells, which have the ability to destroy viral-infected or malignant (surfeit of self-peptides) cells.

MHC class I molecules are comprised of two chains: a MHC alpha chain (heavy chain), and a beta2-microglobulin chain (light chain), where only the alpha chain spans the membrane. The alpha chain has three extracellular domains (alpha 1-3, with alpha1 being at the N terminus), a transmembrane region and a C-terminal cytoplasmic tail. The soluble extracellular beta-2 microglobulin chain associates primarily with the alpha-3 domain and is necessary for MHC stability. The alpha1 and alpha2 domains of the alpha chain are referred to as the recognition region, because the peptide antigen binds in a deep groove between these two domains.

GO terms

Biological Process

GO:0002474 antigen processing and presentation of peptide antigen via MHC class I
GO:0006955 immune response
GO:0001916 positive regulation of T cell mediated cytotoxicity

Molecular Function

GO:0042605 peptide antigen binding

Cellular Component

GO:0042612 MHC class I protein complex

Contributing signatures

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