Tetraspanins are a group of hydrophobic membrane proteins that interact with a wide variety of proteins including intracellular signaling molecules, integrins and membrane receptors. Members of the tetraspanin family are characterized by the presence of four hydrophobic domains and play a role in cell development, activation, growth and motility. TSPAN6 (tetraspanin-6), also known as A15 homolog, putative NF-kappa-B-activating protein 321, T245 protein, tetraspanin TM4-D or TM4SF6 (transmembrane 4 superfamily member 6), is a 245 amino acid multi-pass membrane protein that belongs to the tetraspanin (TM4SF) family. TSPAN6 is expressed at high levels in brain, with lower levels of expression found in colon, lung, pancreas, prostate, retina and melanocytes, as well as fetal heart, liver and spleen. The gene encoding TSPAN6 maps to the human X chromosome.