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On the convergent evolution of animal toxins - conservation of a diad of functional residues in potassium channel-blocking toxins with unrelated structures

Dauplais, M. and Lecoq, A. and Song, J.X. and Cotton, J. and Jamin, N. and Gilquin, B. and Rowan, E.G. and Vita, C. (1997) On the convergent evolution of animal toxins - conservation of a diad of functional residues in potassium channel-blocking toxins with unrelated structures. Journal of Biological Chemistry, 272 (7). pp. 4302-4309. ISSN 0021-9258

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Abstract

BgK is a K+ channel-blocking toxin from the sea anemone Bunodosoma granulifera It is a 37-residue protein that adopts a novel fold, as determined by NMR and modeling. An alanine-scanning-based analysis revealed the functional importance of five residues, which include a critical lysine and an aromatic residue separated by 6.6 ± 1.0 Å. The same diad is found in the three known homologous toxins from sea anemones. More strikingly, a similar functional diad is present in all K+ channel-blocking toxins from scorpions, although these toxins adopt a distinct scaffold. Moreover, the functional diads of potassium channel-blocking toxins from sea anemone and scorpions superimpose in the three-dimensional structures. Therefore, toxins that have unrelated structures but similar functions possess conserved key functional residues, organized in an identical topology, suggesting a convergent functional evolution for these small proteins.