Five amphipathic peptides with antimicrobial, hemolytic, and insecticidal activity were isolated from the crude venom of the wolf spider Oxyopes kitabensis. The peptides, named oxyopinins, are the largest linear cationic amphipathic peptides from the venom of a spider that have been chemically characterized at present. According to their primary structure Oxyopinin 1 is composed of 48 amino acid residues showing extended sequence similarity to the ant insecticidal peptide ponericinL2 and to the frog antimicrobial peptide dermaseptin. Oxyopinins 2a, 2b, 2c, and 2d have highly similar sequences. At least 27 out of 37 amino acid residues are conserved. They also show a segment of sequence similar to ponericinL2. Circular dichroism analyses showed that the secondary structure of the five peptides is essentially ␣-helical. Oxyopinins showed disrupting activities toward both biological membranes and artificial vesicles, particularly to those rich in phosphatidylcholine. Electrophysiological recordings performed on insect cells (Sf9) showed that the oxyopinins produce a drastic reduction of cell membrane resistance by opening non-selective ion channels. Additionally, a new paralytic neurotoxin named Oxytoxin 1 was purified from the same spider venom. It contains 69 amino acid residue cross-linked by five disulfide bridges. Application of mixtures containing oxyopinins and Oxytoxin 1 to insect larvae showed a potentiation phenomenon, by which an increase lethality effect is observed. These results suggest that the linear amphipathic peptides in spider venoms and neuropeptides cooperate to capture insects efficiently.Amphipathic and cationic ␣-helical peptides are broadly found in animals as a part of their biological defense system (1).Since the discovery of melittins (2) and cecropins (3) a large number of amphiphilic and cationic peptides have been characterized in invertebrates, especially from the phyla Arthropoda and in vertebrates from the class Amphibia. Linear cationic peptides with ␣-helical conformation share some common characteristics such as antimicrobial activities at low micromolar concentrations and ␣-helix formation in hydrophobic environments. However, other features distinguish them such as their disruptive activity toward eukaryotic cells, particularly red blood cells, and their hydrophilic/hydrophobic amino acid distribution along the structure. In arthropods, based on the source of the antimicrobial peptides, these molecules could be roughly classified in two types. The first type is cecropin-like peptides, which are antimicrobial with low hemolytic activity acting as a part of the insect immune defense system against the invasion of pathogenic microorganisms. This type of molecule is mainly found in the hemolymph of various arthropods such as sarcotoxin A in house fly (4), cecropins in lepidoptera (3), and spinigerin in termites (5). The second type is melittinlike peptides, which are antimicrobial with hemolytic activity higher than that of the first type acting mainly as weapons for capturing pr...

SummarySeveral hundred disulfide-bridged neurotoxic peptides have been characterized from scorpion venom; however, only few scorpion venom peptides without disulfide bridges have been identified and characterized. These non-disulfide-bridged peptides (NDBPs) are a novel class of molecules because of their unique antimicrobial, immunological or cellular signaling activities. This review provides an overview of their structural simplicity, precursor processing, biological activities and evolution, and sheds insight into their potential clinical and agricultural applications. Based on their pharmacological activities and peptide size similarity, we have classified these peptides into six subfamilies. IUBMB Life, 57: 13 -21, 2005

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Scorpion ␤-toxins affect the activation of voltage-sensitive sodium channels (NaChs). Although these toxins have been instrumental in the study of channel gating and architecture, little is known about their active sites. By using an efficient system for the production of recombinant toxins, we analyzed by point mutagenesis the entire surface of the ␤-toxin, Bj-xtrIT, an anti-insect selective excitatory toxin from the scorpion Buthotus judaicus. Each toxin mutant was purified and analyzed using toxicity and binding assays, as well as by circular dichroism spectroscopy to discern the differences among mutations that caused structural changes and those that specifically affected bioactivity. This analysis highlighted a functional discontinuous surface of 1405 Å 2 , which was composed of a number of non-polar and three charged amino acids clustered around the main ␣-helical motif and the C-tail. Among the charged residues, Glu 30 is a center of a putative "hot spot" in the toxin-receptor binding-interface and is shielded from bulk solvent by a hydrophobic "gasket" (Tyr 26 and Val 34 ). Comparison of the Bj-xtrIT structure with that of other ␤-toxins that are active on mammals suggests that the hot spot and an adjacent non-polar region are spatially conserved. These results highlight for the first time structural elements that constitute a putative "pharmacophore" involved in the interaction of ␤-toxins with receptor site-4 on NaChs. Furthermore, the unique structure of the C-terminal region most likely determines the specificity of excitatory toxins for insect NaChs.

Six peptide toxins (Magi 1^6) were isolated from the Hexathelidae spider Macrothele gigas. The amino acid sequences of Magi 1, 2, 5 and 6 have low similarities to the amino acid sequences of known spider toxins. The primary structure of Magi 3 is similar to the structure of the palmitoylated peptide named PlTx-II from the North American spider Plectreurys tristis (Plectreuridae). Moreover, the amino acid sequence of Magi 4, which was revealed by cloning of its cDNA, displays similarities to the Na + channel modi¢er N N-atracotoxin from the Australian spider Atrax robustus (Hexathelidae). Competitive binding assays using several 125 I-labelled peptide toxins clearly demonstrated the speci¢c binding a⁄nity of Magi 1^5 to site 3 of the insect sodium channel and also that of Magi 5 to site 4 of the rat sodium channel. Only Magi 6 did not compete with the scorpion toxin LqhK KIT in binding to site 3 despite high toxicity on lepidoptera larvae of 3.1 nmol/g. The K i s of other toxins were between 50 pM for Magi 4 and 1747 nM for Magi 1. In addition, only Magi 5 binds to both site 3 in insects (K i = 267 nM) and site 4 in rat brain synaptosomes (K i = 1.2 nM), whereas it showed no a⁄nities for either mammal binding site 3 or insect binding site 4. Magi 5 is the ¢rst spider toxin with binding a⁄nity to site 4 of a mammalian sodium channel. ß