Mutating a critical lysine in ShK toxin alters its binding configuration in the pore-vestibule region of the voltage-gated potassium channel, Kv1.3.

The voltage-gated potassium channel in T lymphocytes, Kv1.3, an important target for immunosuppressants, is blocked by picomolar concentrations of the polypeptide ShK toxin and its analogue ShK-Dap22. ShK-Dap22 shows increased selectivity for Kv1.