title: Experimental conversion of a defensin into a neurotoxin: implications for origin of toxic function.
abstract: Scorpion K(+) channel toxins and insect defensins share a conserved three-dimensional structure and related biological activities (defense against competitors or invasive microbes by disrupting their membrane functions), which provides an ideal system to study how functional evolution occurs in a conserved structural scaffold. Using an experimental approach, we show that the deletion of a small loop of a parasitoid venom defensin possessing the "scorpion toxin signature" (STS) can remove steric hindrance of peptide-channel interactions and result in a neurotoxin selectively inhibiting K(+) channels with high affinities. This insect defensin-derived toxin adopts a hallmark scorpion toxin fold with a common cysteine-stabilized α-helical and β-sheet motif, as determined by nuclear magnetic resonance analysis. Mutations of two key residues located in STS completely diminish or significantly decrease the affinity of the toxin on the channels, demonstrating that this toxin binds to K(+) channels in the same manner as scorpion toxins. Taken together, these results provide new structural and functional evidence supporting the predictability of toxin evolution. The experimental strategy is the first employed to establish an evolutionary relationship of two distantly related protein families.
authors.affiliation: Group of Animal Innate Immunity, State Key Laboratory of Integrated Management of Pest Insects & Rodents, Institute of Zoology, Chinese Academy of Sciences, Chaoyang District, Beijing, China.
authors.forename: Shunyi
authors.initials: S
authors.lastname: Zhu
authors.forename: Steve
authors.initials: S
authors.lastname: Peigneur
authors.forename: Bin
authors.initials: B
authors.lastname: Gao
authors.forename: Yoshitaka
authors.initials: Y
authors.lastname: Umetsu
authors.forename: Shinya
authors.initials: S
authors.lastname: Ohki
authors.forename: Jan
authors.initials: J
authors.lastname: Tytgat
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D023082:Defensins / Q000737:chemistry*; D019143:Evolution, Molecular; D007313:Insecta / Q000378:metabolism; D015640:Ion Channel Gating / Q000187:drug effects; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009498:Neurotoxins / Q000737:chemistry* / Q000378:metabolism / Q000494:pharmacology / Q000633:toxicity*; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D010455:Peptides / Q000737:chemistry / Q000378:metabolism; D010802:Phylogeny; D026902:Potassium Channel Blockers / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology / Q000633:toxicity; D015221:Potassium Channels / Q000737:chemistry / Q000378:metabolism; D011485:Protein Binding / Q000187:drug effects; D012604:Scorpion Venoms / Q000737:chemistry* / Q000378:metabolism; D014981:Xenopus
chemical_list: D023082:Defensins; D009498:Neurotoxins; D010455:Peptides; D026902:Potassium Channel Blockers; D015221:Potassium Channels; D012604:Scorpion Venoms
keywords: experimental evolution; functional diversification; parasitic wasp; potassium channel; scorpion toxin; venom