Laser Raman studies on cobrotoxin

Toxins' classification through Raman spectroscopy with principal component analysis

The method based on the combination of Raman spectroscopy and principal component analysis (PCA) was applied to the set of peptide and protein toxins from animal venoms and to synthetic analogues of peptides. The study demonstrated the possibility of toxin classification according to their primary and secondary structures based on Raman spectroscopy. The method described here allows discrimination of snake venom three-finger toxins from predatory marine mollusks α-conotoxins. Moreover, PCA of the Raman spectra of toxins revealed differences within the group of three-finger toxins and also within the group of conotoxins, related to their spatial structure. In particular, on the basis of the developed technique it is possible to distinguish the disulfide isomers of the same peptide toxin. The results obtained have been confirmed by bioinformatic methods. So, we have proposed a method for the rapid analysis of newly discovered venom-derived protein or peptide toxins by establishing their similarity with other already studied toxins by referring to a particular class. Taking into account a low specimen consumption by Raman spectroscopy, the proposed method could represent a first step in the study of toxins from rare and/or endangered venomous animals. The ability to distinguish configuration of disulfide bonds allows to synthesize the correct isomer of the toxin.

Label-free SERS characterization of snake venoms by exploring the cysteine environs with bone-shaped gold nanoparticles

Identification of snake venoms is a vital step in the treatment of fatal snakebites. In this study, we use the gold-thiolate interaction between a cysteine residue and gold nanoparticles to establish a SERS method for the differentiation of the venoms of Trimeresurus stejnegeri and Bungarus multicinctus. We confirm the preference of gold nanoparticles over silver for the SERS study of snake venoms by a binding experiment that also functions to differentiate the two venom samples by colorimetry and UV-vis spectroscopy. We report the SERS spectra of Trimeresurus stejnegeri and Bungarus multicinctus venoms for the first time. The spectra display distinct SERS signatures of the snake venoms on bone-shaped gold nanoparticles made with a house recipe. These signatures correlate to selected segments of the venom proteins due to the anchoring effect of the gold-cysteine bond. The method is quick as it accomplishes in situ isolation of the structure of interest to avoid tedious purification of the samples. The location of the interactive cysteine residue makes a novel characteristic of proteins in general.

Conformational properties of the neurotoxins and cytotoxins isolated from Elapid snake venoms

The review will critically assess the information available on the conformation of homologous neurotoxins and cytotoxins isolated from Elapid snakes. Particular attention will be given to the dynamics of the molecules in solution because there is the possibility that defined intramolecular rearrangements are involved at the sites of action. Such properties will be then reconciled with the known X-ray crystallographic and sequence data in order to derive likely structure-activity relationships.

Reversed unfolding-refolding process of cobra neurotoxin

Circular dichroism and nuclear magnetic resonance spectroscopies have been used to study the unfolding process of cobrotoxin upon addition of fluoro alcohols/or sodium dodecyl sulfate to its aqueous solution. In each final unfolded state, the protein had its disulfide bonds intact. The unfolding process has been found to be reversible in the case of fluoro alcohol/water mixtures, while no such reversibility was found in the case of sodium dodecyl sulfate. However, when hexafluoro-2-propanol is added to the sodium dodecyl sulfate unfolded protein, refolding is induced. The mechanism of unfolding is discussed in terms of the different interactions which govern the protein conformation in solution.

Laser Raman studies on the conformation of Pro-Leu-Gly-NH2

Laser Raman spectra of Pro-Leu-Gly-NH2, the factor that inhibits release of pituitary melanotropin, have been obtained in the solid state, in dimethylsuloxide and in aqueous solution. The amide I frequencies were observed at 1650 and 1687 cm-1 in the solid state and at 1669 cm-1 in dimethylsulfoxide. The conformation of this tripeptide has been proposed by 1H-NMR studies in [2H]-dimethylsulfoxide and revealed by X-ray analysis to be type II beta-turn. These observed amide I frequencies thus are characteristic of type II beta-turn conformation. The relatively lower amide I frequency, 1645 cm-1, observed in 2H2O indicates that the conformation of the peptide in aqueous solution could be different from those in solid state and in dimethylsulfoxide. pH changes hae no significant effect on aqueous solution spectra, except for the shape of the amide III band. The maximum of the amide III band shifted from 1259 cm-1 at pH 2.0 to 1242 cm-1 at pH 11.7. The amide III peaks in the solid state were at 1234 and 1268 cm-1.

Raman spectra of some snake venom components

The Raman spectra of aqueous solutions of cobrotoxin, erabutoxin b (short-chain neurotoxins), alpha-bungarotoxin (a long-chain neurotoxin), cardiotoxin, cytotoxin I (cardiotoxins), 6-carboxyl-modified cobrotoxin and cobrotoxin treated with 5 M guanidine-HCl (denatured neurotoxins) were investigated. The main-chain structure of the toxins was found to consist predominantly of beta-pleated sheets and random-coils. The relative amounts of the beta-conformations were estimated to be in order of: cardiotoxins approximately short-chain neurotoxins greater than long-chain neurotoxins greater than Laticauda semifasciata III (exceptionally weak neurotoxin). Most of the disulfide-bridges of every toxin take the gauche-gauche structure about the CC-SS-CC linkage. However, the number of gauche-gauche structures is not the same among the neurotoxins. Tyr-25 of cobrotoxin is found to form a strong hydrogen bond similar to that of other short-chain neurotoxins investigated earlier.