Major histocompatibility complex: Difference between revisions

Both Class I and Class II MHC molecules are heterodimers with two extracellular subunits ( and  and one or two transmembrane helices that extend from the extracellular subunits to the cytoplasm. In Class I molecules, the  subunit is divided into three domains (and). The anddomains form a -sheet platform with two -helix rails that serve as the peptide-binding groove. The domain forms an immunoglobin-like fold that carries the peptide-binding groove with added support from with the subunit (a 2-microglobulin molecule encoded outside of the MHC Class I gene locus). In Class II molecules, both the  and subunits are divided into two domains (and). The peptide-binding groove is formed by the  and domains and the  and domains carry the peptide-binding groove. While the  subunit is polymorphic for both MHC Classes, the  subunit is polymorphic only for Class II molecules.