Kv1.2 channel-specific blocker from Mesobuthus eupeus scorpion venom: Structural basis of selectivity

Scorpion venom is an unmatched source of selective high-affinity ligands of potassium channels. There is a high demand for such compounds to identify and manipulate the activity of particular channel isoforms. The objective of this study was to obtain and characterize a specific ligand of voltage-gated potassium channel K(v)1.2. As a result, we report the remarkable selectivity of the peptide MeKTx11-1 (alpha-KTx 1.16) from Mesobuthus eupeus scorpion venom to this channel isoform. MeKTx11-1 is a high-affinity blocker of Kv1.2 (IC50 similar to 0.2 nM), while its activity against K(v)1.1, K(v)1.3, and K(v)1.6 is 10 000, 330 and 45 000 fold lower, respectively, as measured using the voltage-clamp technique on mammalian channels expressed in Xenopus oocytes. Two substitutions, G9V and P37S, convert MeKTx11-1 to its natural analog MeKTx11-3 (alpha-KTx 1.17) having 15 times lower activity and reduced selectivity to Kv1.2. We produced MeKTx11-1 and MeKTx11-3 as well as their mutants MeKTx11-1(G9V) and MeKTx11-1(P37S) recombinantly and demonstrated that point mutations provide an intermediate effect on selectivity. Key structural elements that explain MeKTx11-1 specificity were identified by molecular modeling of the toxin-channel complexes. Confirming our molecular modeling predictions, site-directed transfer of these elements from the pore region of K(v)1.2 to K(v)1.3 resulted in the enhanced sensitivity of mutant K(v)1.3 channels to MeKTx11-1. We conclude that MeKTx11-1 may be used as a selective tool in neurobiology.