[Show abstract][Hide abstract] ABSTRACT: Scorpion toxins are important pharmacological tools for probing the physiological roles of ion channels which are involved in many physiological processes and as such have significant therapeutic potential. The discovery of new scorpion toxins with different specificities and affinities is needed to further characterize the physiology of ion channels. In this regard, a new short polypeptide called Kbot21 has been purified to homogeneity from the venom of Buthus occitanus tunetanus scorpion. Kbot21 is structurally related to BmBKTx1 from the venom of the Asian scorpion Buthus martensii Karsch. These two toxins differ by only two residues at position 13 (R /V) and 24 (D/N).Despite their very similar sequences, Kbot21 and BmBKTx1 differ in their electrophysiological activities. Kbot21 targets KV channel subtypes whereas BmBKTx1 is active on both big conductance (BK) and small conductance (SK) Ca2+-activated K+ channel subtypes, but has no effects on Kv channel subtypes. The docking model of Kbot21 with the Kv1.2 channel shows that the D24 and R13 side-chain of Kbot21 are critical for its interaction with KV channels.
PLoS ONE 09/2015; 10(9):e0137611. DOI:10.1371/journal.pone.0137611 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In this study, a validated method using a thermal desorber combined with a gas chromatograph coupled to mass spectrometry was used to identify the volatile organic compounds released during decomposition of 6 human and 26 animal remains in a laboratory environment during a period of 6 months. 452 compounds were identified. Among them a human specific marker was sought using principle component analysis. We found a combination of 8 compounds (ethyl propionate, propyl propionate, propyl butyrate, ethyl pentanoate, pyridine, diethyl disulfide, methyl(methylthio)ethyl disulfide and 3-methylthio-1-propanol) that led to the distinction of human and pig remains from other animal remains. Furthermore, it was possible to separate the pig remains from human remains based on 5 esters (3-methylbutyl pentanoate, 3-methylbutyl 3-methylbutyrate, 3-methylbutyl 2-methylbutyrate, butyl pentanoate and propyl hexanoate). Further research in the field with full bodies has to corroborate these results and search for one or more human specific markers. These markers would allow a more efficiently training of cadaver dogs or portable detection devices could be developed.
PLoS ONE 09/2015; 10(9):e0137341. DOI:10.1371/journal.pone.0137341 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The toxin, previously described as a "non-toxic" toxin, was isolated from the scorpion venom of Tityus serrulatus (Ts), responsible for the most severe and the highest number of accidents in Brazil. In this study, the subtype specificity and selectivity of Ts4 was investigated using six mammalian Nav channels (Nav1.2→Nav1.6 and Nav1.8) and two insect Nav channels (DmNav1 and BgNav). The electrophysiological assays showed that Ts4 specifically inhibited the fast inactivation of Nav1.6 channels, the most abundant sodium channel expressed in the adult central nervous system, and can no longer be classified as a "non-toxic peptide". Based on the results, we could classify the Ts4 as a classical α-toxin. The Ts4 3D-structural model was built based on the solved X-ray Ts1 3D-structure, the major toxin from Ts venom with which it shares high sequence identity (65.57%). The Ts4 model revealed a flattened triangular shape constituted by three-stranded antiparallel β-sheet and one α-helix stabilized by four disulfide bonds. The absence of a Lys in the first amino acid residue of the N-terminal of Ts4 is probably the main responsible for its low toxicity. Other key amino acid residues important to the toxicity of α- and β-toxins are discussed here.
[Show abstract][Hide abstract] ABSTRACT: Sponges of the genus Agelas produce compounds that modulate the activity of voltage-gated sodium ion channels and contribute novel scaffolds for the development of compounds with activity against a plethora of biological targets. In particular, clathrodin and dibromosceptrin were reported to decrease the average maximum amplitude of inward sodium currents in isolated chick embryo sympathetic ganglia cells; we envisaged these compounds as a starting point to design novel Nav channel modulators. This endeavor was part of our long-term goal of designing a comprehensive library of Agelas alkaloid analogs that would cover a broader chemical space and allow us to examine the activity of such compounds on Nav channels. Our series of compounds was designed by maintaining the terminal structural features found in clathrodin while rigidizing the central part of the molecule and replacing the 3-aminopropene linker with a 4-methylenepiperazine moiety. Synthesised compounds were screened for inhibitory action against the human voltage-gated sodium channel isoforms Nav 1.3, Nav 1.4, cardiac Nav 1.5, and Nav 1.7 using an automated patch clamp electrophysiology technique. The results demonstrate that we have obtained a series of compounds with a modest but selective inhibitory activity against the Nav 1.3 channel isoform. The most potent compound showed selective activity against the Nav 1.3 channel isoform with an IC50 of 19 μM and is a suitable starting point for further development of selective Nav 1.3 channel modulators. Such compounds could prove to be beneficial as a pharmacological tool towards the development of novel therapeutically useful compounds in the treatment of pain.
Medicinal Chemistry Research 06/2015; 24(6):2366-2380. DOI:10.1007/s00044-014-1300-x · 1.40 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Cyclic nucleotide-sensitive ion channels are molecular pores that open in response to cAMP or cGMP, which are universal second messengers. Binding of a cyclic nucleotide to the carboxyterminal cyclic nucleotide binding domain (CNBD) of these channels is thought to cause a conformational change that promotes channel opening. The C-linker domain, which connects the channel pore to this CNBD, plays an important role in coupling ligand binding to channel opening. Current structural insight into this mechanism mainly derives from X-ray crystal structures of the C-linker/CNBD from hyperpolarization-activated cyclic nucleotide-modulated (HCN) channels. However, these structures reveal little to no conformational changes upon comparison of the ligand-bound and unbound form. In this study, we take advantage of a recently identified prokaryote ion channel, SthK, which has functional properties that strongly resemble cyclic nucleotide-gated (CNG) channels and is activated by cAMP, but not by cGMP. We determined X-ray crystal structures of the C-linker/CNBD of SthK in the presence of cAMP or cGMP. We observe that the structure in complex with cGMP, which is an antagonist, is similar to previously determined HCN channel structures. In contrast, the structure in complex with cAMP, which is an agonist, is in a more open conformation. We observe that the CNBD makes an outward swinging movement, which is accompanied by an opening of the C-linker. This conformation mirrors the open gate structures of the Kv1.2 channel or MthK channel, which suggests that the cAMP-bound C-linker/CNBD from SthK represents an activated conformation. These results provide a structural framework for better understanding cyclic nucleotide modulation of ion channels, including HCN and CNG channels.
PLoS ONE 01/2015; 10(1):e0116369. DOI:10.1371/journal.pone.0116369 · 3.23 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Conotoxins are venom peptides from cone snails with multiple disulfide bridges that provide a rigid structural scaffold. Typically
acting on ion channels implicated in neurotransmission, conotoxins are of interest both as tools for pharmacological studies
and as potential new medicines. δ-Conotoxins act by inhibiting inactivation of voltage-gated sodium channels (Nav). Their pharmacology has not been extensively studied because their highly hydrophobic character makes them difficult targets
for chemical synthesis. Here we adopted an acid-cleavable solubility tag strategy that facilitated synthesis, purification,
and directed disulfide bridge formation. Using this approach we readily produced three native δ-conotoxins from Conus consors plus two rationally designed hybrid peptides. We observed striking differences in Nav subtype selectivity across this group of compounds, which differ in primary structure at only three positions: 12, 23, and
25. Our results provide new insights into the structure-activity relationships underlying the Nav subtype selectivity of δ-conotoxins. Use of the acid-cleavable solubility tag strategy should facilitate synthesis of other
hydrophobic peptides with complex disulfide bridge patterns.