To function,<unk>  forms a dimer, consisting of a pair of<unk>  chains. The most common form of<unk>  is composed of a<unk> -α and<unk> -β chain, both members of the immunoglobulin superfamily with an immunoglobulin variable (IgV)-like extracellular domain connected to the membrane by a thin stalk, and an intracellular tail. Less-common homodimers of the<unk> -α chain are also expressed on some cells. The molecular weight of each<unk>  chain is about 34 kDa. The structure of the<unk>  molecule was determined by Leahy, D.J., Axel, R., and Hendrickson, W.A. by X-ray Diffraction at a 2.6A resolution. The structure was determined to have an immunoglobulin-like beta-sandwich folding and 114 amino acid residues. 2% of the protein is wound into α-helices and 46% into β-sheets, with the remaining 52% of the molecules remaining in the loop portions. Schematic representation of the heterodimeric<unk>  co-receptor
CD8
CD4
CD74
CD137
CD22
CD23
CDV3 
CD44