Pore-forming toxin

Pore-forming proteins (PFTs, also known as pore-forming toxins) are usually produced by bacteria, and include a number of protein exotoxins but may also be produced by other organisms such as apple snails that produce perivitellin-2 or earthworms, who produce lysenin. They are frequently cytotoxic (i.e., they kill cells), as they create unregulated pores in the membrane of targeted cells. PFTs can be divided into two categories, depending on the alpha-helical or beta-barrel architecture of their transmembrane channel that can consist either of Alpha-pore-forming toxins e.g., Haemolysin E family, actinoporins, Corynebacterial porin B, Cytolysin A of E. coli. Beta-barrel pore-forming toxins e.g. α-hemolysin (Fig 1), PVL – Panton-Valentine leukocidin, various insecticidal toxins. Other categories: Large beta-barrel pore-forming toxins MACPF and Cholesterol-dependent cytolysins (CDCs), gasdermin Binary toxins e.g., Anthrax toxin, Pleurotolysin Small pore-forming toxins e.g., Gramicidin A According to TCDB, there are following families of pore-forming toxins: 1.C.3 α-Hemolysin (αHL) family 1.C.4 Aerolysin family 1.C.5 ε-toxin family 1.C.11 RTX-toxin superfamily 1.C.12 Membrane attack complex/perforin superfamily 1.C.13 Leukocidin family 1.C.14 Cytohemolysin (CHL) family 1.C.39 Thiol-activated cholesterol-dependent cytolysin family 1.C.43 Lysenin family 1.C.56 Pseudomonas syringae HrpZ cation channel family 1.C.57 Clostridial cytotoxin family 1.C.74 Snake cytotoxin (SCT) family 1.C.97 Pleurotolysin pore-forming family β-PFTs are so-named because of their structural characteristics: they are composed mostly of β-strand-based domains. They have divergent sequences, and are classified by Pfam into a number of families including Leukocidins, Etx-Mtx2, Toxin-10, and aegerolysin. X-ray crystallographic structures have revealed some commonalities: α-hemolysin and Panton-Valentine leukocidin S are structurally related. Similarly, aerolysin and Clostridial Epsilon-toxin. and Mtx2 are linked in the Etx/Mtx2 family.