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To function, CD8 forms a dimer, consisting of a pair of CD8 chains. The most common form of CD8 is composed of a CD8-α and CD8-β chain, both members of the [[ immunoglobulin superfamily]] with an [[Immunoglobulin domain|immunoglobulin variable (IgV) -like extracellular domain]] connected to the membrane by a thin stalk, and an intracellular tail. Less-common homodimers of the CD8-α chain are also expressed on some cells. The molecular weight of CD8 is about 13 ,463.2 Da. The structure of the CD8 molecule was determined by Leahy, D.J., Axel, R., and Hendrickson, W.A. by X-ray Diffraction at a 2 .6A resolution.<ref name="pmid1547508"/> 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.
Image:CD8_receptor.PNG| thumb| none| left|Schematic representation of the heterodimeric CD8 [[co-receptor]]]]