Abstract

This communication reports the structural and functional characterization of urotoxin, the first K⁺ channel toxin isolated from the venom of the Australian scorpion Urodacus yaschenkoi. It is a basic peptide consisting of 37 amino acids with an amidated C-terminal residue. Urotoxin contains eight cysteines forming four disulfide bridges with sequence similarities resembling the α-potassium channel toxin 6 (α-KTx-6) subfamily of peptides; it was assigned the systematic number of α-KTx-6.21. Urotoxin is a potent blocker of human voltage-gated potassium channel (K_v)1.2 channels, with an IC₅₀ of 160 pM, whereas its affinity for other channels tested was in the nanomolar range (hK_v1.1, IC₅₀ = 253 nM; hK_v1.3, IC₅₀ = 91 nM; and hK_Ca3.1, IC₅₀ = 70 nM). The toxin had no effect on hK_v1.4, hK_v1.5, human ether-à-go-go–related gene type 1 (hERG1), or human ether-à-go-go–like (hELK2) channels. Multiple sequence alignments from the venom gland transcriptome showed the existence of four other new peptides similar to urotoxin. Computer modeling of urotoxin’s three-dimensional structure suggests the presence of the α/β-scaffold characteristic of other scorpion toxins, although very likely forming an uncommon disulfide pairing pattern. Using molecular dynamics, a model for the binding of this peptide to human K_v1.2 and hK_v1.1 channels is presented, along with the binding of an in silico mutant urotoxin (Lys25Ala) to both channels. Urotoxin enriches our knowledge of K⁺ channel toxins and, due to its high affinity for hK_v1.2 channels, it may be a good candidate for the development of pharmacologic tools to study the physiologic functions of K⁺ channels or related channelopathies and for restoring axonal conduction in demyelinated axons.