The structure of the Staphylococcus aureus α-hemolysin pore has been determined to 1.9 Å resolution. Contained within the mushroom-shaped homo- oligomeric heptamer is a solvent-filled channel, 100 Å in length, that runs along the sevenfold axis and ranges from 14 Å to 46 Å in diameter. The lytic, transmembrane domain comprises the lower half of a 14-strand antiparallel β barrel, to which each protomer contributes two β strands, each 65 Å long. The interior of the β barrel is primarily hydrophilic, and the exterior has a hydrophobic belt 28 Å wide. The structure proves the heptameric subunit stoichiometry of the α-hemolysin oligomer, shows that a glycine-rich and solvent-exposed region of a water-soluble protein can self- assemble to form a transmembrane pore of defined structure, and provides insight into the principles of membrane interaction and transport activity of β barrel pore-forming toxins.
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