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.This superfamily represents MHC class I and II-like antigen-recognition domains from:MHC class II, N-terminal domains of alpha and beta chains []MHC class I, alpha-1 and alpha-2 domains []MHC class I related proteins, such as gammadelta T-cell ligand [], Ulbp3 [], Fc (IgG) receptor (alpha-1 and -2 domains) [], CD1 (alpha-1 and -2 domains) [], zinc-alpha-2-glycoprotein ZAG (fat depleting factor) []Immunomodulatory protein m144, alpha-1 and alpha-2 domains []Haemochromatosis protein Hfe, alpha-1 and alpha-2 domains []NK cell ligand RAE-1 beta []Endothelial protein C receptor (phospholipid-binding protein) []
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 [, ]. 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. This entry represents MHC antigen-recognition-like domains from:MHC class I, alpha-1 and alpha-2 domains []MHC class I homologue gammadelta T-cell ligand []MHC class I related Ulbp3 []MHC class I related Fc (IgG) receptor, alpha-1 and alpha-2 domains []MHC class I related CD1, alpha-1 and alpha-2 domains []MHC class I related zinc-alpha-2-glycoprotein ZAG (fat depleting factor) []Immunomodulatory protein m144, alpha-1 and alpha-2 domains []Haemochromatosis protein Hfe, alpha-1 and alpha-2 domains []Endothelial protein C receptor (phospholipid-binding protein) []NK cell ligand RAE-1 []. RAE-1 proteins (alpha, beta, delta, and gamma) are distant major histocompatibility complex (MHC) class I homologues, comprising isolated alpha-1 alpha-2 domains, and lack alpha3 domains [].
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 [, ]. 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. This entry represents MHC antigen-recognition-like domains from:MHC class I, alpha-1 and alpha-2 domains []MHC class I homologue gammadelta T-cell ligand []MHC class I related Ulbp3 []MHC class I related Fc (IgG) receptor, alpha-1 and alpha-2 domains []MHC class I related CD1, alpha-1 and alpha-2 domains []MHC class I related zinc-alpha-2-glycoprotein ZAG (fat depleting factor) []Immunomodulatory protein m144, alpha-1 and alpha-2 domains []Haemochromatosis protein Hfe, alpha-1 and alpha-2 domains []Endothelial protein C receptor (phospholipid-binding protein) []NK cell ligand RAE-1 []. RAE-1 proteins (alpha, beta, delta, and gamma) are distant major histocompatibility complex (MHC) class I homologues, comprising isolated alpha-1 alpha-2 domains, and lack alpha3 domains [].
