 HLA-DR is an αβ heterodimer, cell surface receptor, each subunit of which contains two extracellular domains, a membrane-spanning domain and a cytoplasmic tail.Both α and β chains are anchored in the membrane.The N-terminal domain of the mature protein forms an alpha-helix that constitutes the exposed part of the binding groove, the C-terminal cytoplasmic region interact with the other chain forming a beta-sheet under the binding groove spanning to the cell membrane.