Subunit stoichiometry of staphylococcal alpha-hemolysin in crystals and on membranes: a heptameric transmembrane pore

摘要: Elucidation of the accurate subunit stoichiometry oligomeric membrane proteins is fraught with complexities. The interpretations chemical cross-linking, analytical ultracentrifugation, gel filtration, and low-resolution electron microscopy studies are often ambiguous. Staphylococcal alpha-hemolysin (alpha HL), a homooligomeric toxin that forms channels in cell membranes, was believed to possess six subunits arranged around sixfold axis symmetry. Here, we report analysis x-ray diffraction data modification experiments indicate alpha HL oligomer heptamer. Self-rotation functions calculated using from single crystals oligomers show sevenfold rotational pore formed on rabbit erythrocyte membranes determined be heptamer by electrophoretic separation heteromers charge wild-type additional negative generated targeted single-cysteine mutant. These establish heptameric oligomerization state transmembrane both three-dimensional biological membrane.