α-hemolysin, γ-hemolysin, and leukocidin from Staphylococcus aureus: Distant in sequence but similar in structure

α-Hemolysin from Staphylococcus aureus assembles from a water-soluble, monomeric species to a membrane-bound heptamer on the surface of target cells, creating water-filled channels that lead to cell death and lysis. Staphylococcus aureus also produces the γ-hemolysin and leukocidin toxins, which function as two component toxins in the disruption and lysis of erythrocytes and leukocytes. Analysis of the aligned sequences of α- hemolysin, γ-hemolysin, and leukocidin in the context of the α-hemolysin heptamer structure supports the conclusion that even though the level of sequence identity between α-hemolysin and the γ-hemolysin and leukocidin toxins is in the so-called twilight zone, the three-dimensional structures of the protomers are probably conserved. By analogy with α-hemolysin, γ- hemolysin and leukocidin may also form oligomeric, transmembrane channels in which an antiparallel β-barrel constitutes the primary membrane-embedded domain.