title: Functional evolution of scorpion venom peptides with an inhibitor cystine knot fold.
abstract: The ICK (inhibitor cystine knot) defines a large superfamily of polypeptides with high structural stability and functional diversity. Here, we describe a new scorpion venom-derived K+ channel toxin (named λ-MeuKTx-1) with an ICK fold through gene cloning, chemical synthesis, nuclear magnetic resonance spectroscopy, Ca2+ release measurements and electrophysiological recordings. λ-MeuKTx-1 was found to adopt an ICK fold that contains a three-strand anti-parallel β-sheet and a 310-helix. Functionally, this peptide selectively inhibits the Drosophila Shaker K+ channel but is not capable of activating skeletal-type Ca2+ release channels/ryanodine receptors, which is remarkably different from the previously known scorpion venom ICK peptides. The removal of two C-terminal residues of λ-MeuKTx-1 led to the loss of the inhibitory activity on the channel, whereas the C-terminal amidation resulted in the emergence of activity on four mammalian K+ channels accompanied by the loss of activity on the Shaker channel. A combination of structural and pharmacological data allows the recognition of three putative functional sites involved in channel blockade of λ-MeuKTx-1. The presence of a functional dyad in λ-MeuKTx-1 supports functional convergence among scorpion venom peptides with different folds. Furthermore, similarities in precursor organization, exon-intron structure, 3D-fold and function suggest that scorpion venom ICK-type K+ channel inhibitors and Ca2+ release channel activators share a common ancestor and their divergence occurs after speciation between buthidae and non-buthids. The structural and functional characterizations of the first scorpion venom ICK toxin with K+ channel-blocking activity sheds light on functionally divergent and convergent evolution of this conserved scaffold of ancient origin.
authors.affiliation: Group of Animal Innate Immunity, State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences, 1 Beichen West Road, Chaoyang District, Beijing 100101, People's Republic of China.
authors.forename: Bin
authors.initials: B
authors.lastname: Gao
authors.forename: Peta J
authors.initials: PJ
authors.lastname: Harvey
authors.forename: David J
authors.initials: DJ
authors.lastname: Craik
authors.forename: Michel
authors.initials: M
authors.lastname: Ronjat
authors.forename: Michel
authors.initials: M
authors.lastname: De Waard
authors.forename: Shunyi
authors.initials: S
authors.lastname: Zhu
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002118:Calcium / Q000378:metabolism; D003001:Cloning, Molecular; D003553:Cystine / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D019143:Evolution, Molecular; D008958:Models, Molecular; D008969:Molecular Sequence Data; D010455:Peptides / Q000737:chemistry* / Q000235:genetics* / Q000494:pharmacology; D026902:Potassium Channel Blockers / Q000737:chemistry* / Q000378:metabolism* / Q000494:pharmacology; D058849:Protein Refolding; D017433:Protein Structure, Secondary; D012604:Scorpion Venoms / Q000737:chemistry* / Q000235:genetics* / Q000494:pharmacology; D012605:Scorpions / Q000737:chemistry / Q000235:genetics*; D014981:Xenopus
chemical_list: D010455:Peptides; D026902:Potassium Channel Blockers; D012604:Scorpion Venoms; D003553:Cystine; D002118:Calcium