title: Molecular divergence of two orthologous scorpion toxins affecting potassium channels.
abstract: Alpha-KTxs are a diverse group of scorpion short-chain peptide toxins that affect animal potassium channels. We report the biochemical purification, gene cloning, and functional characterization of a new α-KTx named MeuTx3B, from venom of the scorpion Mesobuthus eupeus. MeuTx3B is an orthologue of BmTx3B/Martentoxin (α-KTx16 subfamily) from Mesobuthus martensii that differs by three amino acid substitutions. We found that despite their orthologous relationship, MeuTx3B and BmTx3B exhibit different post-transcriptional processing patterns due to nucleotide mutations in their untranslated regions (UTRs). Our results show that MeuTx3B also differs functionally from BmTx3B in that it lacks inhibitory activity on large conductance calcium-activated potassium channels (BK), implicating the amino acids of difference in conferring the inhibitory activity of BmTx3B. Furthermore, we show that MeuTx3B (2μM) partially inhibits human voltage-gated potassium channel Kv1.3. By using codon-substitution models, we detected signals of positive selection that could drive adaptive evolution of MeuTx3B and related toxins in the functional region associated with pharmacological diversification of toxins in the α-KTx 1 and 16 subfamilies.
authors.affiliation: Group of Animal Innate Immunity, State Key Laboratory of Integrated Management of Pest Insects & Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China.
authors.forename: Bin
authors.initials: B
authors.lastname: Gao
authors.forename: Steve
authors.initials: S
authors.lastname: Peigneur
authors.forename: Julie
authors.initials: J
authors.lastname: Dalziel
authors.forename: Jan
authors.initials: J
authors.lastname: Tytgat
authors.forename: Shunyi
authors.initials: S
authors.lastname: Zhu
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002460:Cell Line; D002851:Chromatography, High Pressure Liquid; D017931:DNA Primers; D006801:Humans; D016013:Likelihood Functions; D008969:Molecular Sequence Data; D015221:Potassium Channels / Q000187:drug effects*; D012604:Scorpion Venoms / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid; D014118:Toxins, Biological / Q000737:chemistry / Q000235:genetics / Q000633:toxicity*; D020506:Untranslated Regions
chemical_list: D017931:DNA Primers; D015221:Potassium Channels; D012604:Scorpion Venoms; D014118:Toxins, Biological; D020506:Untranslated Regions