Figure 1.

Formation of a switchable pore in the plasma membrane of rod photoreceptors. α-Toxin of Staphylococcus aureus is a self-assembling, pore-forming protein. Heptameric α-toxin pores are inserted in the plasma membrane of rod cells, allowing nucleotide and ion exchange between intra- and extracellular compartments. In a mutated form of the toxin (H5K8A), the amino acids 130–134 have been replaced by five histidines to facilitate pore closure by Zn²⁺ ions. This mechanism is reversible by chelation of Zn²⁺ with EDTA. Note that the depicted components are not to scale.