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Venoms comprise of complex mixtures of peptides evolved for predation and defensive purposes. Remarkably, some carnivorous cone snails can inject two distinct venoms in response to predatory or defensive stimuli, providing a unique opportunity to study separately how different ecological pressures contribute to toxin diversification. Here, we report the extraordinary defensive strategy of the Rhizoconus subgenus of cone snails. The defensive venom from this worm-hunting subgenus is unusually simple, almost exclusively composed of αD-conotoxins instead of the ubiquitous αA-conotoxins found in the more complex defensive venom of mollusc- and fish-hunting cone snails. A similarly compartmentalized venom gland as those observed in the other dietary groups facilitates the deployment of this defensive venom. Transcriptomic analysis of a Conus vexillum venom gland revealed the αD-conotoxins as the major transcripts, with lower amounts of 15 known and four new conotoxin superfamilies also detected with likely roles in prey capture. Our phylogenetic and molecular evolution analysis of the αD-conotoxins from five subgenera of cone snails suggests they evolved episodically as part of a defensive strategy in the Rhizoconus subgenus. Thus, our results demonstrate an important role for defence in the evolution of conotoxins. [ABSTRACT FROM AUTHOR]

Venom as a form of chemical prey capture is a key innovation that has underpinned the explosive radiation of the advanced snakes (Caenophidia). Small venom proteins are often rich in disulfide bonds thus facilitating stable molecular scaffolds that present key functional residues on the protein surface. New toxin types are initially developed through the venom gland over-expression of normal body proteins, their subsequent gene duplication and diversification that leads to neofunctionalisation as random mutations modify their structure and function. This process has led to preferentially selected (privileged) cysteine-rich scaffolds that enable the snake to build arrays of toxins many of which may lead to therapeutic products and research tools. This review focuses on cysteine-rich small proteins and peptides found in snake venoms spanning natriuretic peptides to phospholipase enzymes, while highlighting their three-dimensional structures and biological functions as well as their potential as therapeutic agents or research tools. [ABSTRACT FROM AUTHOR]

Background and Purpose: ω-Conotoxins CVIE and CVIF (CVIE&F) selectively inhibit Cav2.2 channels and are lead molecules in the development of novel analgesics. At physiological membrane potentials, CVIE&F block of Cav2.2 channels is weakly reversible. To improve reversibility, we designed and synthesized arginine CVIE&F analogues in which arginine was substituted for lysine at position 10 ([R10K]CVIE&F), and investigated their serum stability and pharmacological actions on voltage-gated calcium channels (VGCCs).Experimental Approach: Changes in peptide structure due to R10K substitution were assessed by NMR. Peptide stability in human serum was analysed by reversed-phase HPLC and MS over a 24 h period. Two-electrode voltage-clamp and whole-cell patch clamp techniques were used to study [R10K]CVIE&F effects on VGCC currents in Xenopus oocytes and rat dorsal root ganglion neurons respectively.Key Results: R10K substitution did not change the conserved ω-conotoxin backbone conformations of CVIE&F nor the ω-conotoxin selectivity for recombinant or native Cav2.2 channels, although the inhibitory potency of [R10K]CVIF was better than that of CVIF. At -80 mV, the R10K chemical modification significantly affected ω-conotoxin-channel interaction, resulting in faster onset kinetics than those of CVIE&F. Heterologous and native Cav2.2 channels recovered better from [R10K]CVIE&F block than CVIE&F. In human serum, the ω-conotoxin half-lives were 6-10 h. CVIE&F and [R10K]CVIE&F were more stable than CVID.Conclusions and Implications: R10K substitution in CVIE&F significantly alters the kinetics of ω-conotoxin action and improves reversibility without diminishing conotoxin potency and specificity for the Cav2.2 channel and without diminishing the serum stability. These results may help generate ω-conotoxins with optimized kinetic profiles for target binding. [ABSTRACT FROM AUTHOR]

Background and Purpose ω-Conotoxins CVIE and CVIF ( CVIE& F) selectively inhibit Cav2.2 channels and are lead molecules in the development of novel analgesics. At physiological membrane potentials, CVIE& F block of Cav2.2 channels is weakly reversible. To improve reversibility, we designed and synthesized arginine CVIE& F analogues in which arginine was substituted for lysine at position 10 ([ R10K] CVIE& F), and investigated their serum stability and pharmacological actions on voltage-gated calcium channels ( VGCCs). Experimental Approach Changes in peptide structure due to R10K substitution were assessed by NMR. Peptide stability in human serum was analysed by reversed-phase HPLC and MS over a 24 h period. Two-electrode voltage-clamp and whole-cell patch clamp techniques were used to study [ R10K] CVIE& F effects on VGCC currents in X enopus oocytes and rat dorsal root ganglion neurons respectively. Key Results R10K substitution did not change the conserved ω-conotoxin backbone conformations of CVIE& F nor the ω-conotoxin selectivity for recombinant or native Cav2.2 channels, although the inhibitory potency of [ R10K] CVIF was better than that of CVIF. At −80 mV, the R10K chemical modification significantly affected ω-conotoxin−channel interaction, resulting in faster onset kinetics than those of CVIE& F. Heterologous and native Cav2.2 channels recovered better from [ R10K] CVIE& F block than CVIE& F. In human serum, the ω-conotoxin half-lives were 6−10 h. CVIE& F and [ R10K] CVIE& F were more stable than CVID. Conclusions and Implications R10K substitution in CVIE& F significantly alters the kinetics of ω-conotoxin action and improves reversibility without diminishing conotoxin potency and specificity for the Cav2.2 channel and without diminishing the serum stability. These results may help generate ω-conotoxins with optimized kinetic profiles for target binding. [ABSTRACT FROM AUTHOR]

ABSTRACT Voltage-gated sodium (Nav) channels are responsible for generation and propagation of action potentials throughout the nervous system. Their malfunction causes several disorders and chronic conditions including neuropathic pain. Potent subtype specific ligands are essential for deciphering the molecular mechanisms of Nav channel function and development of effective therapeutics. µ-Conotoxin SIIIA is a potent mammalian Nav1.2 channel blocker that exhibits analgesic activity in rodents. We undertook to reengineer loop 1 through a strategy involving charge alterations and truncations which led to the development of µ-SIIIA mimetics with novel selectivity profiles. A novel [N5K/D15A]SIIIA(3-20) mutant with enhanced net positive charge showed a dramatic increase in its Nav1.2 potency (IC50 of 0.5 nM vs. 9.6 nM for native SIIIA) though further truncations led to loss of potency. Unexpectedly, it appears that SIIIA loop 1 significantly influences its Nav channel interactions despite loop 2 and 3 residues constituting the pharmacophore. This minimal functional conotoxin scaffold may allow further development of selective NaV blockers. © 2013 Wiley Periodicals, Inc. Biopolymers 101: 347-354, 2014. [ABSTRACT FROM AUTHOR]

Chronic pain affects approximately 20% of people worldwide and places a large economic and social burden on society. Despite the availability of a range of analgesics, this condition is inadequately treated, with complete alleviation of symptoms rarely occurring. In the past 30 years, the voltage-gated calcium channels (VGCCs) have been recognized as potential targets for analgesic development. Although the majority of the research has been focused on Ca(v) 2.2 in particular, other VGCC subtypes such as Ca(v) 3.2 have recently come to the forefront of analgesic research. Venom peptides from marine cone snails have been proven to be a valuable tool in neuroscience, playing a major role in the identification and characterization of VGCC subtypes and producing the first conotoxin-based drug on the market, the ω-conotoxin, ziconotide. This peptide potently and selectively inhibits Ca(v) 2.2, resulting in analgesia in chronic pain states. However, this drug is only available via intrathecal administration, and adverse effects and a narrow therapeutic window have limited its use in the clinic. Other Ca(v) 2.2 inhibitors are currently in development and offer the promise of an improved route of administration and safety profile. This review assesses the potential of targeting VGCCs for analgesic development, with a main focus on conotoxins that block Ca(v) 2.2 and the developments made to transform them into therapeutics. [ABSTRACT FROM AUTHOR]

Abstract: The activity of α-conotoxin (α-CTX), ImI, from the vermivorous marine snail Conus imperialis, has been studied on mammalian nicotinic receptors on bovine chromaffin cells and at the rat neuromuscular junction. Synthetic α-CTX ImI was a potent inhibitor of the neuronal nicotinic response in bovine adrenal chromaffin cells (IC50 = 2.5 μM, log IC50 = 0.4 ± 0.07), showing competitive inhibition of nicotine-evoked catecholamine secretion. α-CTX ImI also inhibited nicotine-evoked 45Ca2+ uptake but not 45Ca2+ uptake stimulated by 56 mM K+. In contrast, α-CTX ImI had no effect at the neuromuscular junction over the concentration range 1-20 μM. Bovine chromaffin cells are known to contain the α3β4, α7, and (possibly) α3β4α5 subtypes. However, the secretory response of bovine chromaffin cells is not inhibited by α-bungarotoxin, indicating that α7 nicotinic receptors are not involved. We propose that α-CTX ImI interacts selectively with the functional (α3β4 or α3β4α5) nicotinic acetylcholine receptor to inhibit the neuronal-type nicotinic response in bovine chromaffin cells. [ABSTRACT FROM AUTHOR]

The article presents an abstract of the research paper "Effect of Conantokins on the Spermine Modulation of Glutamate-NMDA Sites in Normal and Alzheimer Disease Human Cerebral Cortex." The research found that the subunit composition of NMDA sites is locally variable and selective differences between controls and Alzheimer's disease cases in key brain regions.