Structural comparison of fungal tetraspanins (Pls1, Tsp2, Tsp3) and tetraspanin like proteins (Tpl1). The Pls1, Tsp2 and Tsp3 tetraspanin families display the typical structure of tetraspanin: four transmembrane domains (TM1, TM2, TM3, TM4, yellow boxes) and a small extracellular loop (ECL1, gray line), a small intracellular loop (ICL, purple line), a large extracellular loop (ECL2, orange line), intracellular N-terminal (black line) and C-terminal (brown line) tails. ECL2 contains a CCG motif and further two conserved cysteine residues (red triangles). A. The Pls1 tetraspanin family contains conserved polar/charged residues in TM1, TM2, TM3 and TM4 (blue lines) and one putative palmitoylation site is proximal to TM4 (green triangle). B. The Tsp2 tetraspanin family displays large intracellular N-terminal and C-terminal tails. One putative conserved palmitoylation site is located at the end of TM4 (green triangle). C. The Tsp3 tetraspanin family has a short ECL1 and a large C-terminal tail. D. The Tpl1 tetraspanin-like proteins lack the typical cysteine-based pattern in their ECL2 (CCG motif and further two conserved cysteine residues). Nevertheless, their ECL2 regions contain two conserved cysteine residues close to TM3 and TM4.