Na + -channel specific scorpion toxins are peptides of 60±76 amino acid residues in length, tightly bound by four disulfide bridges. The complete amino acid sequence of 85 distinct peptides are presently known. For some toxins, the three-dimensional structure has been solved by X-ray diffraction and NMR spectroscopy. A constant structural motif has been found in all of them, consisting of one or two short segments of a-helix plus a triplestranded b-sheet, connected by variable regions forming loops (turns). Physiological experiments have shown that these toxins are modifiers of the gating mechanism of the Na + -channel function, affecting either the inactivation (a-toxins) or the activation (b-toxins) kinetics of the channels. Many functional variations of these peptides have been demonstrated, which include not only the classical a-and b-types, but also the species specificity of their action. There are peptides that bind or affect the function of Na + -channels from different species (mammals, insects or crustaceans) or are toxic to more than one group of animals. Based on functional and structural features of the known toxins, a classification containing 10 different groups of toxins is proposed in this review. Attempts have been made to correlate the presence of certain amino acid residues or`active sites' of these peptides with Na + -channel functions. Segments containing positively charged residues in special locations, such as the five-residue turn, the turn between the second and the third b-strands, the C-terminal residues and a segment of the N-terminal region from residues 2±11, seems to be implicated in the activity of these toxins. However, the uncertainty, and the limited success obtained in the search for the site through which these peptides bind to the channels, are mainly due to the lack of an easy method for expression of cloned genes to produce a well-folded, active peptide. Many scorpion toxin coding genes have been obtained from cDNA libraries and from polymerase chain reactions using fragments of scorpion DNAs, as templates. The presence of an intron at the DNA level, situated in the middle of the signal peptide, has been demonstrated.

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Scorpions are well known for their dangerous stings that can result in severe consequences for human beings, including death. Neurotoxins present in their venoms are responsible for their toxicity. Due to their medical relevance, toxins have been the driving force in the scorpion natural compounds research field. On the other hand, for thousands of years, scorpions and their venoms have been applied in traditional medicine, mainly in Asia and Africa. With the remarkable growth in the number of characterized scorpion venom components, several drug candidates have been found with the potential to tackle many of the emerging global medical threats. Scorpions have become a valuable source of biologically active molecules, from novel antibiotics to potential anticancer therapeutics. Other venom components have drawn attention as useful scaffolds for the development of drugs. This review summarizes the most promising candidates for drug development that have been isolated from scorpion venoms.

Cold allodynia, pain in response to cooling, occurs during or within hours of oxaliplatin infusion and is thought to arise from a direct effect of oxaliplatin on peripheral sensory neurons. To characterize the pathophysiological mechanisms underlying acute oxaliplatin-induced cold allodynia, we established a new intraplantar oxaliplatin mouse model that rapidly developed long-lasting cold allodynia mediated entirely through tetrodotoxin-sensitive Nav pathways. Using selective inhibitors and knockout animals, we found that Nav1.6 was the key isoform involved, while thermosensitive transient receptor potential channels were not involved. Consistent with a crucial role for delayed-rectifier potassium channels in excitability in response to cold, intraplantar administration of the K+-channel blocker 4-aminopyridine mimicked oxaliplatin-induced cold allodynia and was also inhibited by Navl.6 blockers. Intraplantar injection of the Nav1.6-activator Cn2 elicited spontaneous pain, mechanical allodynia and enhanced 4-aminopyridine-induced cold allodynia. These findings provide behavioural evidence for a crucial role of Nav1.6 in multiple peripheral pain pathways including cold allodynia.

SUMMARY The number and types of venom components that affect ion-channel function are reviewed. These are the most important venom components responsible for human intoxication, deserving medical attention, often requiring the use of specific anti-venoms. Special emphasis is given to peptides that recognize Na+-, K+- and Ca++-channels of excitable cells. Knowledge generated by direct isolation of peptides from venom and components deduced from cloned genes, whose amino acid sequences are deposited into databanks are now adays in the order of 1.5 thousands, out of an estimate biodiversity closed to 300,000. Here the diversity of components is briefly reviewed with mention to specific references. Structural characteristic are discussed with examples taken from published work. The principal mechanisms of action of the three different types of peptides are also reviewed. Na+-channel specific venom components usually are modifier of the open and closing kinetic mechanisms of the ion-channels, whereas peptides affecting K+-channels are normally pore blocking agents. The Ryanodine Ca++-channel specific peptides are known for causing sub-conducting stages of the channels conductance and some were shown to be able to internalize penetrating inside the muscle cells.

A novel peptide, scorpine, was isolated from the venom of the scorpion Pandinus imperator, with anti-bacterial activity and a potent inhibitory effect on the ookinete (ED 50 0.7 W WM) and gamete (ED 50 10 W WM) stages of Plasmodium berghei development. It has 75 amino acids, three disulfide bridges with a molecular mass of 8350 Da. Scorpine has a unique amino acid sequence, similar only to some cecropins in its N-terminal segment and to some defensins in its C-terminal region. Its gene was cloned from a cDNA library.z 2000 Federation of European Biochemical Societies.

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The goals of this study are to investigate the mechanism and site of action whereby a human ether-a-go-gorelated gene (HERG)-specific scorpion peptide toxin, ErgTx, suppresses HERG current. We apply cysteinescanning mutagenesis to the S5-P and P-S6 linkers of HERG and examine the resulting changes in ErgTx potency. Data are compared with the characteristics of charybdotoxin (ChTx, or its analogs) binding to the Shaker channel. ErgTx binds to the outer vestibule of HERG but may not physically occlude the pore. In contrast to ChTx⅐Shaker interaction, elevating [K] o (from 2 to 98 mM) does not affect ErgTx potency, and throughsolution electrostatic forces only play a minor role in influencing ErgTx⅐HERG interaction. Cysteine mutations of three positions in S5-P linker (Trp-585, Gly-590, and Ile-593) and 1 position in P-S6 linker (Pro-632) induce profound changes in ErgTx binding (⌬⌬G > 2 kcal/ mol). We propose that the long S5-P linker of the HERG channel forms an amphipathic ␣-helix that, together with the P-S6 linker, forms a hydrophobic ErgTx binding site. This study paves the way for future mutant cycle analysis of interacting residues in the ErgTx⅐HERG complex, which, in conjunction with NMR determination of the ErgTx solution structure, will yield information about the topology of HERG's outer vestibule.