Figure 1. Tetraspanin structural features.

a | Shown in this ‘unfolded’ tetraspanin are membrane-proximal palmitoylations (red), hydrophilic residues within transmembrane domains (grey balls), and extracellular loops (EC1 and EC2). EC2, also called large extracellular loop (LEL) is divided into a constant region, containing A, B and E helices, and a variable region, containing the signature tetraspanin CCG motif, two conserved disulphide bonds (red) and a third loop and disulphide bond (dashed) that appears in some tetraspanins. b | This more realistic scheme emphasizes the close packing of the four transmembrane domains, the proximity of EC1 and EC2, and the overall rod shaped structure of tetraspanins. Disulphide bonds are not shown. This scheme is based on structural results seen for uroplakin tetraspanins UPK1A and UPK1B⁸, and modelled for other tetraspanins^9,10.