What Determines The Charybdotoxin Specificity Among Kv1 Potassium Channels?

Cystine knot peptides found in the venoms of predatory invertebrates have been a valuable source of potassium channels inhibitors. One of the most intensively studied inhibitory cystine knot peptides is charybdotoxin (CTX) from the scorpion Leiurus quinquestriatus. CTX binds to the outer vestibule of certain members of the mammalian Kv1 potassium channel family with high affinity, including Kv1.2 and Kv1.3. However, neither Kv1.4 nor Kv1.5 channels are inhibited by CTX. Starting with a crystal structure of the Kv1.2-CTX complex, we used Rosetta structural modeling to build homology models of the Kv1.4 and Kv1.5 homomers in complex with CTX. When the native CTX sequence was docked to the Kv1.4 and Kv1.5 receptors, Rosetta energy solvation terms for a number of residues at channel-toxin interface scored poorly. Rosetta energies were analyzed to suggest the energy barriers for CTX binding. Multiple steric and electrostatic clashes were apparent in the Kv1.4- and Kv1.5-CTX complexes that were predicted to destabilize the complexes. We used Rosetta design to redesign CTX to mitigate these clashes and energetically complement the binding surface of Kv1.4 and 1.5 channels. This approach suggests a general method for designing pore blocking peptide inhibitors selective for specific ion channel subtypes.