Molecular divergence of two orthologous scorpion toxins affecting potassium channels
Gao, Bin × Peigneur, Steve Dalziel, Julie Tytgat, Jan Zhu, Shunyi #
Comparative Biochemistry and Physiology A, Molecular & Integrative Physiology vol:159 issue:3 pages:313-321
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 alpha-KTx named MeuTx3B, from venom of the scorpion Mesobuthus eupeus. MeuTx3B is an orthologue of BmTx3B/Martentoxin (alpha-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 (2 mu M) 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 alpha-KTx 1 and 16 subfamilies. (C) 2011 Elsevier Inc. All rights reserved.