Aeromonas hydrophila hemolytic component B (AhlB), and similar proteins
This model includes Aeromonas hydrophila hemolytic (Ahl) component B (AhlB) of the tripartite AhlABC toxin, a member of the cytolysin A (ClyA) family of alpha pore-forming toxins (alpha-PFTs). It consists of three proteins, AhlA, AhlB and AhlC, encoded by one operon containing the three genes. Functional and mutagenic studies support a model of pore assembly where the soluble tetrameric form of AhlC first disassociates into monomers, binds a single membrane leaflet, and then recruits AhlB to promote soluble to pore transition; AhlA then binds to form the active hydrophilic lined pore. The structure of AhlB shows an elongated, almost entirely alpha-helical protein, including a hydrophobic beta-hairpin known as a beta-tongue to shield membrane inserting hydrophobic residues. The head domain of AhlB undergoes a large conformational change involving the beta tongue becoming an extended alpha helix, and the tail domain helices sliding relative to one another as AhlB assembles into a hydrophobic pore.
Comment:each of the subunit conformations of AhlB pack together to form a dimer and five of these Type 1/Type 2 dimers assemble into the decameric oligomer
Comment:Other three-component toxins of ClyA family alpha-PFTs include Bacillus cereus Non hemolytic enterotoxin (Nhe) and Hemolysin BL (Hbl). Pore-formation by the Nhe toxin follows a pattern involving membrane binding, oligomerization and finally insertion of the transmembrane regions to form the pore.
Structure:6GRJ: Aeromonas hydrophila AhlB toxin interacts with neighboring molecules of a decameric assembly; contacts at 4.0A
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