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| [[Image:MHC I processing.jpg|thumb|200px|right|'''MHC I presentation pathway, courtesy of B. Catchpole, 2008''']] | | [[Image:MHC I processing.jpg|thumb|200px|right|'''MHC I presentation pathway, courtesy of B. Catchpole, 2008''']] |
| ===Structure=== | | ===Structure=== |
− | * MHC class I is expressed on virtually all nucleated cells
| + | MHC class I is expressed on virtually all nucleated cells and consists of a membrane-associated heavy chain bound non-covalently with a secreted light chain. The heavy chain is made up of three distinct extracellular protein domains - &alpha1, &alpha2 and &alpha3. The heavy chain C - terminus is cytoplasmic. |
− | * MHC class I consists of a membrane-associated heavy chain bound non-covalently with a secreted light chain
| + | |
− | ** Heavy chain:
| + | The light chain is known as β2-microglobulin and is similar in structure to one of the heavy chain domains. It is not membrane associated but binds to the α3-domain of the heavy chain |
− | *** Made up of three distinct extracellular protein domains
| + | [[Image:MHC I Structure.jpg|thumb|right|175px| Structure of MHC I molecule - Copyright Prof Dirk Werling DrMedVet PhD MRCVS]] |
− | **** α1, α2 and α3
| + | |
− | *** The C- terminus is cytoplasmic
| + | The MHC class I domains are structurally and genetically related to immunoglobulin and TcR domains; the outer domains (&alpha1 and &alpha2) are like the variable domains and the &alpha3 domain and &beta2m are like the constant domains. |
− | ** Light chain:
| + | |
− | *** Known as β2-microglobulin
| + | MHC class I molecules are folded to form specific 3-dimensional structures. The α1 and α2 domains are folded to produce an antigen-binding groove which can bind molecules of a limited size only (8-10 amino acids). This limits the size of epitope seen by the T-cell receptors. |
− | *** Similar in structure to one of the heavy chain domains
| |
− | *** Not membrane associated
| |
− | **** But binds to the α3-domain of the heavy chain
| |
− | [[Image:MHC I Structure.jpg|thumb|right|150px| Structure of MHC I molecule - Copyright Prof Dirk Werling DrMedVet PhD MRCVS]] | |
− | * The MHC class I domains are structurally and genetically related to immunoglobulin and TcR domains
| |
− | ** The outer domains (α1 and α2) are like the variable domains
| |
− | ** The α3 domain and β2m are like thrconstant domains
| |
− | * MHC class I molecules are folded to form specific 3-dimensional structures
| |
− | ** The α1 and α2 domains are folded to produce an antigen-binding groove
| |
− | *** This groove can bind molecules of a limited size only (8-10 amino acids)
| |
− | **** This limits the size of epitope seen by the T-cell receptors
| |
| | | |
| ===Presentation Pathway=== | | ===Presentation Pathway=== |