Identification and molecular characterization of three new K+-channel specific toxins from the Chinese scorpion Mesobuthus martensii Karsch revealing intronic number polymorphism and alternative splicing in duplicated genes

K+-channel specific toxins from scorpions are powerful probes used in the structural and functional characterization of different subfamilies of K+-channels which are thought to be the most diverse ion channels. However, only a limited number of K+-channel toxins have been identified from scorpions so far; moreover, little is known about the mechanisms for the generation of a combinatorial peptide library in a venom gland of a scorpion. Here, we identified and characterized three new K+-channel toxin-like peptides from the scorpion Mesobuthus martensii Karsch, which were referred to as BmKcug1, BmKcug2 and BmKcugx, respectively. BmKcug1 and BmKcug2 are two new members of alpha-KTx1 subfamily, and have been classified as alpha-KTx1.14 and alpha-KTx1.15, respectively. BmKcugx represents a new subfamily of K+-channel specific toxins which was classified into alpha-KTx22. BmKcugx was thus classified as alpha-KTx22.1. Genomic analysis demonstrated that BmKcugx gene has two exons interrupted by an intron inserted in the signal peptide encoding region, whereas BmKcug1a (a close homologue of BmKcug1)/BmKcug2 gene was interrupted by two introns, located within the 5'UTR of the gene and in the signal peptide encoding region, respectively. Transcriptomic analysis for the venom glands of M. martensii Karsch indicated that the abundances of the transcripts of BmKcug1a and BmKcug2 are much higher than that of BmKcugx; it suggests that the intron in 5'UTR could markedly increase the expression level of the K+-channel toxins. Alignment of the genomic sequences of BmKcug1a and BmKcug2 revealed that an alternative splicing event occurred at the intron 1-exon 2 junction in the 5'UTR of BmKcug2 transcript. (C) 2011 Elsevier Inc. All rights reserved.