Genomic structure of a potassium channel toxin from Heteractis magnifica¹

Abstract

We provide information on the gene encoding the K + channel toxin, HmK, of the sea anemone Heteractis magnified. A series of DNA amplifications by PCR, which included the amplification of the 5'-untranslated region of the gene, showed that an intron of 402 nucleotides separated the sequence that encodes the matured toxin from the signal peptide sequence. A second 264 nucleotide intron interrupted the 5'-untranslated region of the previously reported HmK cDNA. Two possible transcription-initiation sites were identified by primer extension analysis. Corresponding TATA-box consensus sequences, characteristic of a promoter region, were also located from PCR products of uncloned libraries of adaptor-ligated genomic DNA fragments. The coding region for matured HmK is intronless. The same is also true for other sea anemone toxins reported thus far. More notably, a similar intron-exon organization is present in other ion channel-blocking toxins from scorpions implying that molecules having similar functions share a similar organization at the genomic level suggesting a common path of evolution.

Sea anemone toxins affecting voltage-gated sodium channels – molecular and evolutionary features

“…3). Interestingly, this structure organization is also found in genes encoding unrelated sea anemone potassium channel blockers (Gendeh et al, 1997) and scorpion toxins (Zhu and Gao, 2006). The similar gene structures organization can be attributed to convergent evolution and may suggest that these introns have a selective value, which is corroborated by examples of critical roles of introns in gene expression (reviewed by Maniatis and Reed, 2002; Fedorova and Fedorov, 2003).…”

“…They immobilize their prey or deter their foe by using cells called nematocytes for stinging and delivery of venom. Analysis of the venom in many sea anemone species uncovered a rich repertoire of low molecular weight compounds such as serotonin and histamine (Beress, 1982), ~20 kDa pore-forming polypeptide toxins (Kem, 1988; Anderluh and Macek, 2002), 3.5–6.5 kDa polypeptide toxins active on voltage-gated potassium channels (Castaneda et al, 1995, Schweitz et al, 1995; Gendeh et al, 1997; Yeung et al, 2005) and 3–5 kDa polypeptide toxins active on voltage-gated sodium channels (Beress et al, 1975; Rathmayer et al, 1976; Honma and Shiomi, 2006). The combination combined effects of these compounds has apparently been successful over hundreds of millions of years as is evident by the success ability of sea anemones to colonize and thrive in a wide variety of ecological niches.…”

Development of a sea anemone toxin as an immunomodulator for therapy of autoimmune diseases

“…GenBank Accession numbers are listed next to each sequence. Many of these sea anemone toxin sequences have been characterized for K + channel-blocking activity (Castaneda et al, 1995; Cotton et al, 1997; Gendeh et al, 1997a; Gendeh et al, 1997b; Honma et al, 2008; Shiomi, 2009) (Yamaguchi et al, 2011). B, A phylogenetic tree based on the multiple sequence alignment and generated with the PHYLIP program (http://www.genebee.msu.su/genebee.html): ShK (ShK-Tx) and toxins from six other sea anemones (S. mertensii [SmK-Tx], S. haddoni [ShaK-Tx], S. gigantean [SgK-Tx], T. aster [TaK-Tx], C. adhaesivum [CaK-Tx], H. magnifica [HhK-Tx]) have the same number of residues as ShK, share remarkable sequence similarity, and cluster in one sub-group.…”

Sea Anemone (Cnidaria, Anthozoa, Actiniaria) Toxins: An Overview

“…The introns-exon junctions that are typical donor and acceptor splice sites have followed the GT/AG rule, in which the introns begin with GT and end with AG [131]. In the work of Gendeh and co-workers [142] on HmK, a similar organization on introns-exon junction in scorpion toxins has been reported, suggesting that molecules with similar functions have similar organization at genomic level, therefore implying a common evolutionary path.…”