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1.  Structure of the analgesic μ-conotoxin KIIIA and effects on structure and function of disulfide deletion†,‡ 
Biochemistry  2009;48(6):1210-1219.
The μ-conotoxin μ-KIIIA, from Conus kinoshitai, blocks mammalian neuronal voltage-gated sodium channels (VGSCs) and is a potent analgesic following systemic administration in mice. We have determined its solution structure using NMR spectroscopy. Key residues identified previously as being important for activity against VGSCs (Lys7, Trp8, Arg10, Asp11, His12 and Arg14) all reside on an α-helix with the exception of Arg14. To further probe structure-activity relationships of this toxin against VGSC subtypes, we have characterised the analogue μ-KIIIA[C1A,C9A], in which the Cys residues involved in one of the three disulfides in μ-KIIIA were replaced with Ala. Its structure is quite similar to that of μ-KIIIA, indicating that the Cys1-Cys9 disulfide bond could be removed without any significant distortion of the α-helix bearing the key residues. Consistent with this, μ-KIIIA[C1A,C9A] retained activity against VGSCs, with its rank order of potency being essentially the same as that of μ-KIIIA, namely, NaV1.2 > NaV1.4 > NaV1.7 ≥ NaV1.1 > NaV1.3 > NaV1.5. Kinetics of block were obtained for NaV1.2, NaV1.4 and NaV1.7, and in each case both kon and koff values of μ-KIIIA[C1A,C9A] were larger than those of μ-KIIIA. Our results show that the key residues for VGSC binding lie mostly on an α-helix and that the first disulfide bond can be removed without significantly affecting the structure of this helix, although the modification accelerates the on- and off-rates of the peptide against all tested VGSC subtypes. These findings lay the groundwork for the design of minimized peptides and helical mimetics as novel analgesics.
doi:10.1021/bi801998a
PMCID: PMC4153535  PMID: 19170536
2.  Expanding Chemical Diversity of Conotoxins: Peptoid-Peptide Chimeras of the Sodium Channel Blocker µ-KIIIA and its Selenopeptide Analogues 
The µ-conotoxin KIIIA is a three disulfide-bridged blocker of voltage-gated sodium channels (VGSCs). The Lys7 residue in KIIIA is an attractive target for manipulating the selectivity and efficacy of this peptide. Here, we report the design and chemical synthesis of µ-conopeptoid analogues (peptomers) in which we replaced Lys7 with peptoid monomers of increasing side-chain size: N-methylglycine, N-butylglycine and N-octylglycine. In the first series of analogues, the peptide core contained all three disulfide bridges; whereas in the second series, a disulfide-depleted selenoconopeptide core was used to simplify oxidative folding. The analogues were tested for functional activity in blocking the Nav1.2 subtype of mammalian VGSCs exogenously expressed in Xenopus oocytes. All six analogues were active, with the N-methylglycine analogue, [Sar7]KIIIA, the most potent in blocking the channels while favoring lower efficacy. Our findings demonstrate that the use of N-substituted Gly residues in conotoxins show promise as a tool to optimize their pharmacological properties as potential analgesic drug leads.
doi:10.1016/j.ejmech.2013.04.041
PMCID: PMC4332556  PMID: 23707919
µ-conotoxins; KIIIA, peptomers; selenocysteine; diselenide; sodium channels; electrophysiology
3.  µ-Conotoxin KIIIA Derivatives with Divergent Affinities versus Efficacies in Blocking Voltage-gated Sodium Channels 
Biochemistry  2010;49(23):4804-4812.
The possibility of independently manipulating the affinity and efficacy of pore-blocking ligands of sodium channels is of interest for the development of new drugs for the treatment of pain. The analgesic µ-conotoxin KIIIA, a 16-residue peptide with three disulfide bridges, is a pore-blocker of voltage-gated sodium channels, including the neuronal subtype NaV1.2 (Kd of 5 nM). At saturating concentrations, µ-KIIIA incompletely blocks the sodium current of NaV1.2, leaving a 5% residual current (rINa). Lys7 is an important residue: the mutation K7A decreases both the efficacy (i.e., increases rINa to 23%) and the affinity of the peptide (Kd, 115 nM). In this report, various replacements of residue 7 were examined to determine whether affinity and efficacy were inexorably linked. Because of their facile chemical synthesis, KIIIA analogs were used that had as a core structure the disulfide-depleted KIIIA[C1A,C2U,C9A,C5U] (where U is selenocysteine) or ddKIIIA. The analogs ddKIIIA and ddKIIIA[K7X], where X represents one of nine different amino acids, were tested on voltage-clamped Xenopus oocytes expressing rat NaV1.2 or NaV1.4. Their affinities ranged from 0.01 to 36 µM and rINa's from 2 to 42%, and these two variables appeared uncorrelated. Instead, rINa varied inversely with side chain size, and remarkably charge and hydrophobicity appeared inconsequential. The ability to manipulate a µ-conopeptide's affinity and efficacy, as well as its capacity to interfere with subsequent tetrodotoxin-binding, greatly expands its scope as a reagent to probe sodium channel structure and function, and may also lead to the development of µ-conotoxins as safe analgesics.
doi:10.1021/bi100207k
PMCID: PMC2907105  PMID: 20459109
4.  Distinct disulfide isomers of μ-conotoxins KIIIA and KIIIB block voltage-gated sodium channels 
Biochemistry  2012;51(49):9826-9835.
In the preparation of synthetic conotoxins containing multiple disulfide bonds, oxidative folding can produce numerous permutations of disulfide bond connectivities. Establishing the native disulfide connectivities thus presents a significant challenge when the venom-derived peptide is not available, as is increasingly the case when conotoxins are identified from cDNA sequences. Here, we investigate the disulfide connectivity of μ-conotoxin KIIIA, which was predicted originally to have a [C1-C9,C2-C15,C4-C16] disulfide pattern based on homology with closely-related μ-conotoxins. The two major isomers of synthetic μ-KIIIA formed during oxidative folding were purified and their disulfide connectivities mapped by direct mass spectrometric CID fragmentation of the disulfide-bonded polypeptides. Our results show that the major oxidative folding product adopts a [C1-C15,C2-C9,C4-C16] disulfide connectivity, while the minor product adopts a [C1-C16,C2-C9,C4-C15] connectivity. Both of these peptides were potent blockers of NaV1.2 (Kd 5 and 230 nM, respectively). The solution structure for μ-KIIIA based on NMR data was recalculated with the [C1-C15,C2-C9,C4-C16] disulfide pattern; its structure was very similar to the μ-KIIIA structure calculated with the incorrect [C1-C9,C2-C15,C4-C16] disulfide pattern, with an α-helix spanning residues 7–12. In addition, the major folding isomers of μ-KIIIB, an N-terminally extended isoform of μ-KIIIA identified from its cDNA sequence, were isolated. These folding products had the same disulfide connectivities as for μ-KIIIA, and both blocked NaV1.2 (Kd 470 and 26 nM, respectively). Our results establish that the preferred disulfide pattern of synthetic μ-KIIIA/μ-KIIIB folded in vitro is 1-5/2-4/3-6 but that other disulfide isomers are also potent sodium channel blockers. These findings raise questions about the disulfide pattern(s) of μ-KIIIA in the venom of Conus kinoshitai; indeed, the presence of multiple disulfide isomers in the venom could provide a means to further expand the snail's repertoire of active peptides.
doi:10.1021/bi301256s
PMCID: PMC4131687  PMID: 23167564
5.  Structure, dynamics and selectivity of the sodium channel blocker µ-conotoxin SIIIA†,‡ 
Biochemistry  2008;47(41):10940-10949.
µ-SIIIA, a novel µ-conotoxin from Conus striatus, appeared to be a selective blocker of tetrodotoxin-sensitive sodium channels in frog preparations. It also exhibited potent analgesic activity in mice, although its selectivity profile against mammalian sodium channels remained unknown. We have determined the structure of µ-SIIIA in aqueous solution and characterized its backbone dynamics by NMR and its functional properties electrophysiologically. Consistent with the absence of hydroxyprolines, µ-SIIIA adopts a single conformation with all peptide bonds in the trans conformation. The C-terminal region contains a well-defined helix encompassing residues 11–16, while residues 3–5 in the N-terminal region form a helix-like turn resembling 310 helix. The Trp12 and His16 side chains are in close proximity, as in the related conotoxin µ-SmIIIA, but Asn2 is further away. Dynamics measurements show that the N-terminus and Ser9 have larger magnitude motions on the sub-ns timescale, while the C-terminus is more rigid. Cys4, Trp12 and Cys13 undergo significant conformational exchange on µs - ms timescales. µ-SIIIA is a potent, nearly irreversible blocker of NaV1.2, but also blocks NaV1.4 and NaV1.6 with submicromolar potency. The selectivity profile of µ-SIIIA, including poor activity against the cardiac sodium channel, NaV1.5, is similar to that of the closely related µ-KIIIA, suggesting that the C-terminal regions of both are critical for blocking neuronal NaV1.2. The structural and functional characterization described in this paper of an analgesic µ-conotoxin that targets neuronal subtypes of mammalian sodium channels provides a basis for the design of novel analogues with an improved selectivity profile.
doi:10.1021/bi801010u
PMCID: PMC4201628  PMID: 18798648
6.  Structurally-Minimized μ-Conotoxin Analogs as Sodium Channel Blockers: Implications for Designing Conopeptide-Based Therapeutics 
ChemMedChem  2009;4(3):406-414.
Disulfide bridges, which stabilize the native conformation of conotoxins impose a challenge in the synthesis of smaller analogs. In this work, we describe the synthesis of a minimized analog of the analgesic μ-conotoxin KIIIA that blocks two sodium channel subtypes, the neuronal NaV1.2 and skeletal muscle NaV1.4. Three disulfide-deficient analogs of KIIIA were initially synthesized in which the native disulfide bridge formed between either C1-C9, C2-C15 or C4-C16 was removed. Deletion of the first bridge only slightly affected the peptide’s bioactivity. To further minimize this analog, the N-terminal residue was removed and two non-essential Ser residues were replaced by a single 5-amino-3-oxapentanoic acid residue. The resulting “polytide” analog retained the ability to block sodium channels and to produce analgesia. Until now, the peptidomimetic approach applied to conotoxins has progressed only modestly at best; thus, the disulfide-deficient analogs containing backbone spacers provide an alternative advance toward the development of conopeptide-based therapeutics.
doi:10.1002/cmdc.200800292
PMCID: PMC4074532  PMID: 19107760
conopeptide; conotoxin; sodium channels; backbone spacers; disulfide bridges
7.  Disulfide-Depleted Selenoconopeptides: Simplified Oxidative Folding of Cysteine-Rich Peptides 
ACS Medicinal Chemistry Letters  2010;1(4):140-144.
Despite the therapeutic promise of disulfide-rich, peptidic natural products, their discovery and structure/function studies have been hampered by inefficient oxidative folding methods for their synthesis. Here we report that converting the three disulfide-bridged μ-conopeptide KIIIA into a disulfide-depleted selenoconopeptide (by removal of a noncritical disulfide bridge and substitution of another disulfide bridge with a diselenide bridge) dramatically simplified its oxidative folding while preserving the peptide’s ability to block voltage-gated sodium channels. The simplicity of synthesizing disulfide-depleted selenopeptide analogues containing a single disulfide bridge allowed rapid positional scanning at Lys7 of μ-KIIIA, resulting in the identification of K7L as a mutation that improved the peptide’s selectivity in blocking a neuronal (Nav1.2) over a muscle (Nav1.4) subtype of sodium channel. The disulfide-depleted selenopeptide strategy offers regioselective folding compatible with high-throughput chemical synthesis and on-resin oxidation methods, and thus shows great promise to accelerate the use of disulfide-rich peptides as research tools and drugs.
doi:10.1021/ml900017q
PMCID: PMC2911238  PMID: 20676359
Conotoxins; diselenide bridges; selenocysteines; oxidative folding; disulfide-rich peptides
8.  Systematic Study of Binding of µ-Conotoxins to the Sodium Channel NaV1.4 
Toxins  2014;6(12):3454-3470.
Voltage-gated sodium channels (NaV) are fundamental components of the nervous system. Their dysfunction is implicated in a number of neurological disorders, such as chronic pain, making them potential targets for the treatment of such disorders. The prominence of the NaV channels in the nervous system has been exploited by venomous animals for preying purposes, which have developed toxins that can block the NaV channels, thereby disabling their function. Because of their potency, such toxins could provide drug leads for the treatment of neurological disorders associated with NaV channels. However, most toxins lack selectivity for a given target NaV channel, and improving their selectivity profile among the NaV1 isoforms is essential for their development as drug leads. Computational methods will be very useful in the solution of such design problems, provided accurate models of the protein-ligand complex can be constructed. Using docking and molecular dynamics simulations, we have recently constructed a model for the NaV1.4-µ-conotoxin-GIIIA complex and validated it with the ample mutational data available for this complex. Here, we use the validated NaV1.4 model in a systematic study of binding other µ-conotoxins (PIIIA, KIIIA and BuIIIB) to NaV1.4. The binding mode obtained for each complex is shown to be consistent with the available mutation data and binding constants. We compare the binding modes of PIIIA, KIIIA and BuIIIB to that of GIIIA and point out the similarities and differences among them. The detailed information about NaV1.4-µ-conotoxin interactions provided here will be useful in the design of new NaV channel blocking peptides.
doi:10.3390/toxins6123454
PMCID: PMC4280544  PMID: 25529306
sodium channels; conotoxins; homology modeling; docking; molecular dynamics; potential of mean force; binding free energy
9.  Disulfide-Depleted Selenoconopeptides: a Minimalist Strategy to Oxidative Folding of Cysteine-Rich Peptides 
ACS medicinal chemistry letters  2010;1(4):140-144.
Despite the therapeutic promise of disulfide-rich, peptidic natural products, their discovery and structure/function studies have been hampered by inefficient oxidative folding methods for their synthesis. Here we report that converting the three disulfide-bridged μ-conopeptide KIIIA into a disulfide-depleted selenoconopeptide (by removal of a noncritical disulfide bridge and substitution of a disulfide- with a diselenide-bridge) dramatically simplified its oxidative folding while preserving the peptide’s ability to block voltage-gated sodium channels. The simplicity of synthesizing disulfide-depleted selenopeptide analogs containing a single disulfide bridge allowed rapid positional scanning at Lys7 of μ-KIIIA, resulting in the identification of K7L as a mutation that improved the peptide’s selectivity in blocking a neuronal (Nav1.2) over a muscle (Nav1.4) subtype of sodium channel. The disulfide-depleted selenopeptide strategy offers regioselective folding compatible with high throughput chemical synthesis and on-resin oxidation methods, and thus shows great promise to accelerate the use of disulfide-rich peptides as research tools and drugs.
PMCID: PMC2911238  PMID: 20676359
conotoxins; diselenide bridges; selenocysteines; oxidative folding; disulfide-rich peptides
10.  Synergistic and Antagonistic Interactions between Tetrodotoxin and μ-Conotoxin in Blocking Voltage-gated Sodium Channels 
Channels (Austin, Tex.)  2009;3(1):32-38.
Tetrodotoxin (TTX) is the quintessential ligand of voltage-gated sodium channels (NaVs). Like TTX, μ-conotoxin peptides are pore blockers, and both toxins have helped to define the properties of neurotoxin receptor Site 1 of NaVs. Here, we report unexpected results showing that the recently discovered μ-conotoxin KIIIA and TTX can simultaneously bind to Site 1 and act in concert. Results with saturating concentrations of peptide applied to voltage-clamped Xenopus oocytes expressing brain NaV1.2, and single-channel recordings from brain channels in lipid bilayers, show that KIIIA or its analog, KIIIA[K7A], block partially, with a residual current that can be completely blocked by TTX. In addition, the kinetics of block by TTX and peptide are each affected by the prior presence of the other toxin. For example, bound peptide slows subsequent binding of TTX (an antagonistic interaction) and slows TTX dissociation when both toxins are bound (a synergistic effect on block). The overall functional consequence resulting from the combined action of the toxins depends on the quantitative balance between these opposing actions. The results lead us to postulate that in the bi-liganded NaV complex, TTX is bound between the peptide and the selectivity filter. These observations refine our view of Site 1 and open new possibilities in NaV pharmacology.
PMCID: PMC2878737  PMID: 19221510
conotoxin; contratoxin; NaV1.2; oocyte; sodium channel; site 1; syntoxin; tetrodotoxin; voltage clamp
11.  The Tetrodotoxin Receptor of Voltage-Gated Sodium Channels—Perspectives from Interactions with μ-Conotoxins 
Marine Drugs  2010;8(7):2153-2161.
Neurotoxin receptor site 1, in the outer vestibule of the conducting pore of voltage-gated sodium channels (VGSCs), was first functionally defined by its ability to bind the guanidinium-containing agents, tetrodotoxin (TTX) and saxitoxin (STX). Subsequent studies showed that peptide μ-conotoxins competed for binding at site 1. All of these natural inhibitors block single sodium channels in an all-or-none manner on binding. With the discovery of an increasing variety of μ-conotoxins, and the synthesis of numerous derivatives, observed interactions between the channel and these different ligands have become more complex. Certain μ-conotoxin derivatives block single-channel currents partially, rather than completely, thus enabling the demonstration of interactions between the bound toxin and the channel’s voltage sensor. Most recently, the relatively small μ-conotoxin KIIIA (16 amino acids) and its variants have been shown to bind simultaneously with TTX and exhibit both synergistic and antagonistic interactions with TTX. These interactions raise new pharmacological possibilities and place new constraints on the possible structures of the bound complexes of VGSCs with these toxins.
doi:10.3390/md8072153
PMCID: PMC2920548  PMID: 20714429
guanidinium toxins; conopeptides; pore block
12.  The Mammalian Neuronal Sodium Channel Blocker μ-Conotoxin BuIIIB has a Structured N-terminus that Influences Potency 
ACS chemical biology  2013;8(6):1344-1351.
Among the μ-conotoxins that block vertebrate voltage-gated sodium channels (VGSCs), some have been shown to be potent analgesics following systemic administration in mice. We have determined the solution structure of a new representative of this family, μ-BuIIIB, and established its disulfide connectivities by direct mass spectrometric collision induced dissociation fragmentation of the peptide with disulfides intact. The major oxidative folding product adopts a 1-4/2-5/3-6 pattern with the following disulfide bridges: Cys5-Cys17, Cys6-Cys23 and Cys13-Cys24. The solution structure reveals that the unique N-terminal extension in μ-BuIIIB, which is also present in μ-BuIIIA and μ-BuIIIC but absent in other μ-conotoxins, forms part of a short α-helix encompassing Glu3 to Asn8. This helix is packed against the rest of the toxin and stabilized by the Cys5-Cys17 and Cys6-Cys23 disulfide bonds. As such, the side chain of Val1 is located close to the aromatic rings of Trp16 and His20, which are located on the canonical helix that displays several residues found to be essential for VGSC blockade in related μ-conotoxins. Mutations of residues 2 and 3 in the N-terminal extension enhanced the potency of μ-BuIIIB for NaV1.3. One analog, [d-Ala2]BuIIIB, showed a 40-fold increase, making it the most potent peptide blocker of this channel characterized to date and thus a useful new tool with which to characterize this channel. Based on previous results for related μ-conotoxins, the dramatic effects of mutations at the N-terminus were unanticipated, and suggest that further gains in potency might be achieved by additional modifications of this region.
doi:10.1021/cb300674x
PMCID: PMC4201638  PMID: 23557677
13.  Conotoxins Targeting Neuronal Voltage-Gated Sodium Channel Subtypes: Potential Analgesics? 
Toxins  2012;4(11):1236-1260.
Voltage-gated sodium channels (VGSC) are the primary mediators of electrical signal amplification and propagation in excitable cells. VGSC subtypes are diverse, with different biophysical and pharmacological properties, and varied tissue distribution. Altered VGSC expression and/or increased VGSC activity in sensory neurons is characteristic of inflammatory and neuropathic pain states. Therefore, VGSC modulators could be used in prospective analgesic compounds. VGSCs have specific binding sites for four conotoxin families: μ-, μO-, δ- and ί-conotoxins. Various studies have identified that the binding site of these peptide toxins is restricted to well-defined areas or domains. To date, only the μ- and μO-family exhibit analgesic properties in animal pain models. This review will focus on conotoxins from the μ- and μO-families that act on neuronal VGSCs. Examples of how these conotoxins target various pharmacologically important neuronal ion channels, as well as potential problems with the development of drugs from conotoxins, will be discussed.
doi:10.3390/toxins4111236
PMCID: PMC3509706  PMID: 23202314
voltage-gated sodium channel; Nav1.3; Nav1.7; Nav1.8; Nav1.9; μ-conotoxin; μO-conotoxin; nociception; analgesic; pain
14.  α–RgIA, a Novel Conotoxin that Blocks the α9α10 nAChR: Structure and Identification of Key Receptor Binding Residues 
Journal of molecular biology  2008;377(4):1216-1227.
α-Conotoxins are small disulfide-constrained peptides from cone snails which act as antagonists at specific subtypes of nicotinic acetylcholine receptors (nAChRs). The 13-residue peptide α-RgIA is a member of the α-4,3 family of α-conotoxins and selectively blocks the α9α10 nAChR subtype, in contrast to another well characterized member of this family, α-ImI, which is a potent inhibitor of the α7 and α3β2 nAChR subtypes. In this study, we have altered side chains in both the 4-residue and 3-residue loops of α-RgIA, and have modified its C-terminus. The effects of these changes on activity against α9α10 and α7 nAChRs were measured, the solution structures of α-RgIA and its Y10W, D5E and P6V analogues were determined from NMR data, and resonance assignments made for α-RgIA[R9A]. The structures for α-RgIA and its three analogues were well-defined except at the chain termini. Comparison of these structures with reported structures of α-ImI reveals a common two-loop backbone architecture within the α-4,3 family, but with variations in side chain solvent accessibility and orientation. Asp5, Pro6 and Arg7 in loop 1 are critical for blockade of both the α9α10 and α7 subtypes. In loop 2, α-RgIA[Y10W] had activity near that of wild-type α-RgIA, with high potency for α9α10 and low potency for α7, and had a similar structure to wild-type. By contrast, Arg9, in loop 2, is critical for specific binding to the α9α10 subtype, probably because it is larger and more solvent accessible than Ala9 in α-ImI. Our findings contribute to a better understanding of the molecular basis for antagonism of the α9α10 nAChR subtype, which is a target for the development of analgesics for treatment of chronic neuropathic pain.
doi:10.1016/j.jmb.2008.01.082
PMCID: PMC2376044  PMID: 18295795
conotoxin; structure; peptide; NMR; nicotinic acetylcholine receptor; pain
15.  Voltage-gated sodium channels were differentially expressed in human normal prostate, benign prostatic hyperplasia and prostate cancer cells 
Oncology Letters  2014;8(1):345-350.
Voltage-gated sodium channels (VGSCs) are expressed not only in excitable cells but also in numerous metastatic cells, particularly in certain types of cancer cells. In some types of cancer, including prostate cancer, the expression of VGSCs is associated with cancer migration, invasion and metastasis in vivo. However, the detailed expression profiles of VGSC α subunits in normal human prostate, in prostatic hyperplasia and prostatic cancer remain controversial. In the present study, quantitative polymerase chain reaction was used to systematically detect all subtypes of VGSC α subunits in normal human prostate, benign prostatic hyperplasia (BPH) and prostate cancer cells. The expression profile of VGSC α subunits was observed to differ between these cell types. Nav1.5 was the major isoform expressed in normal human prostate tissue, while Nav1.5 and Nav1.2 were the predominant isoforms in BPH tissue. However, in PC-3 and LNCaP cells, two typical prostate cancer cell lines, Nav1.6 and Nav1.7 were abundantly expressed. By comparing the relative expression levels of Nav1.5, Nav1.6 and Nav1.7 in these cells, the mRNA levels of Nav1.6 and Nav1.7 were identified to be 6- to 27-fold higher in PC-3 and LNCaP cells than in either normal or BPH samples (P<0.05); however, Nav1.5 mRNA levels were relatively lower compared with those of Nav1.6 or Nav1.7 in all cells analyzed. To confirm whether Nav1.6 and Nav1.7 expression in cancer cells was functional, a patch-clamp technique was used to record whole-cell currents. A tetrodotoxin-sensitive sodium current was successfully recorded in PC-3 cells, but not in LNCaP cells. It was concluded that although all types of VGSC α subunits exhibited low expression levels in normal prostate and BPH cells, both Nav1.6 and Nav1.7 were significantly upregulated in the prostate cancer cell lines, suggesting these subtypes may be potential diagnostic markers and therapeutic targets for certain types of prostate cancer in humans.
doi:10.3892/ol.2014.2110
PMCID: PMC4063587  PMID: 24959274
voltage-gated sodium channel; mRNA; prostate; cancer; benign prostatic hyperplasia
16.  An in vivo tethered toxin approach for the cell-autonomous inactivation of voltage-gated sodium channel currents in nociceptors 
The Journal of Physiology  2010;588(10):1695-1707.
Understanding information flow in sensory pathways requires cell-selective approaches to manipulate the activity of defined neurones. Primary afferent nociceptors, which detect painful stimuli, are enriched in specific voltage-gated sodium channel (VGSC) subtypes. Toxins derived from venomous animals can be used to dissect the contributions of particular ion currents to cell physiology. Here we have used a transgenic approach to target a membrane-tethered isoform of the conotoxin MrVIa (t-MrVIa) only to nociceptive neurones in mice. T-MrVIa transgenic mice show a 44 ± 7% reduction of tetrodotoxin-resistant (TTX-R) VGSC current densities. This inhibition is permanent, reversible and does not result in functional upregulation of TTX-sensitive (TTX-S) VGSCs, voltage-gated calcium channels (VGCCs) or transient receptor potential (TRP) channels present in nociceptive neurones. As a consequence of the reduction of TTX-R VGSC currents, t-MrVIa transgenic mice display decreased inflammatory mechanical hypersensitivity, cold pain insensitivity and reduced firing of cutaneous C-fibres sensitive to noxious cold temperatures. These data validate the use of genetically encoded t-toxins as a powerful tool to manipulate VGSCs in specific cell types within the mammalian nervous system. This novel genetic methodology can be used for circuit mapping and has the key advantage that it enables the dissection of the contribution of specific ionic currents to neuronal function and to behaviour.
doi:10.1113/jphysiol.2010.187112
PMCID: PMC2887988  PMID: 20308253
17.  An in vivo tethered toxin approach for the cell-autonomous inactivation of voltage-gated sodium channel currents in nociceptors 
The Journal of Physiology  2010;588(Pt 10):1695-1707.
Understanding information flow in sensory pathways requires cell-selective approaches to manipulate the activity of defined neurones. Primary afferent nociceptors, which detect painful stimuli, are enriched in specific voltage-gated sodium channel (VGSC) subtypes. Toxins derived from venomous animals can be used to dissect the contributions of particular ion currents to cell physiology. Here we have used a transgenic approach to target a membrane-tethered isoform of the conotoxin MrVIa (t-MrVIa) only to nociceptive neurones in mice. T-MrVIa transgenic mice show a 44 ± 7% reduction of tetrodotoxin-resistant (TTX-R) VGSC current densities. This inhibition is permanent, reversible and does not result in functional upregulation of TTX-sensitive (TTX-S) VGSCs, voltage-gated calcium channels (VGCCs) or transient receptor potential (TRP) channels present in nociceptive neurones. As a consequence of the reduction of TTX-R VGSC currents, t-MrVIa transgenic mice display decreased inflammatory mechanical hypersensitivity, cold pain insensitivity and reduced firing of cutaneous C-fibres sensitive to noxious cold temperatures. These data validate the use of genetically encoded t-toxins as a powerful tool to manipulate VGSCs in specific cell types within the mammalian nervous system. This novel genetic methodology can be used for circuit mapping and has the key advantage that it enables the dissection of the contribution of specific ionic currents to neuronal function and to behaviour.
doi:10.1113/jphysiol.2010.187112
PMCID: PMC2887988  PMID: 20308253
18.  Lactam Constraints Provide Insights into the Receptor-Bound Conformation of Secretin and Stabilize a Receptor Antagonist 
Biochemistry  2011;50(38):8181-8192.
The natural ligands for family B G protein-coupled receptors are moderate length linear peptides having diffuse pharmacophores. The amino-terminal regions of these ligands are critical for biological activity, with their amino-terminal truncation leading to production of orthosteric antagonists. The carboxyl-terminal regions of these peptides are thought to occupy a ligand-binding cleft within the disulfide-bonded amino-terminal domains of these receptors, with the peptides in amphipathic helical conformations. In the current work, we have characterized the binding and activity of a series of 11 truncated and lactam-constrained secretin(5-27) analogues at the prototypic member of this family, the secretin receptor. One peptide in this series with lactam connecting residues 16 and 20 (c[E16,K20][Y10]sec(5-27)) improved the binding affinity of its unconstrained parental peptide 22-fold, while retaining absence of endogenous biological activity and competitive antagonist characteristics. Homology modeling with molecular mechanics and molecular dynamics simulations established that this constrained peptide occupies the ligand-binding cleft in orientation similar to natural full-length secretin, and provided insights into why this peptide was more effective than other truncated conformationally-constrained peptides in the series. This lactam bridge is believed to stabilize an extended α-helical conformation of this peptide while in solution and to not interfere with critical residue-residue approximations while docked to the receptor.
doi:10.1021/bi2008036
PMCID: PMC3177990  PMID: 21851058
Secretin; secretin receptor; family B G protein-coupled receptor; antagonist; lactam bridge; ligand binding
19.  Molecular Surface of JZTX-V (β-Theraphotoxin-Cj2a) Interacting with Voltage-Gated Sodium Channel Subtype NaV1.4 
Toxins  2014;6(7):2177-2193.
Voltage-gated sodium channels (VGSCs; NaV1.1–NaV1.9) have been proven to be critical in controlling the function of excitable cells, and human genetic evidence shows that aberrant function of these channels causes channelopathies, including epilepsy, arrhythmia, paralytic myotonia, and pain. The effects of peptide toxins, especially those isolated from spider venom, have shed light on the structure–function relationship of these channels. However, most of these toxins have not been analyzed in detail. In particular, the bioactive faces of these toxins have not been determined. Jingzhaotoxin (JZTX)-V (also known as β-theraphotoxin-Cj2a) is a 29-amino acid peptide toxin isolated from the venom of the spider Chilobrachys jingzhao. JZTX-V adopts an inhibitory cysteine knot (ICK) motif and has an inhibitory effect on voltage-gated sodium and potassium channels. Previous experiments have shown that JZTX-V has an inhibitory effect on TTX-S and TTX-R sodium currents on rat DRG cells with IC50 values of 27.6 and 30.2 nM, respectively, and is able to shift the activation and inactivation curves to the depolarizing and the hyperpolarizing direction, respectively. Here, we show that JZTX-V has a much stronger inhibitory effect on NaV1.4, the isoform of voltage-gated sodium channels predominantly expressed in skeletal muscle cells, with an IC50 value of 5.12 nM, compared with IC50 values of 61.7–2700 nM for other heterologously expressed NaV1 subtypes. Furthermore, we investigated the bioactive surface of JZTX-V by alanine-scanning the effect of toxin on NaV1.4 and demonstrate that the bioactive face of JZTX-V is composed of three hydrophobic (W5, M6, and W7) and two cationic (R20 and K22) residues. Our results establish that, consistent with previous assumptions, JZTX-V is a Janus-faced toxin which may be a useful tool for the further investigation of the structure and function of sodium channels.
doi:10.3390/toxins6072177
PMCID: PMC4113750  PMID: 25055801
spider toxin; voltage gated sodium channels; JZTX-V; NaV1.4
20.  Modulation of Mononuclear Phagocyte Inflammatory Response by Liposome-Encapsulated Voltage Gated Sodium Channel Inhibitor Ameliorates Myocardial Ischemia/Reperfusion Injury in Rats 
PLoS ONE  2013;8(9):e74390.
Background
Emerging evidence shows that anti-inflammatory strategies targeting inflammatory monocyte subset could reduce excessive inflammation and improve cardiovascular outcomes. Functional expression of voltage-gated sodium channels (VGSCs) have been demonstrated in monocytes and macrophages. We hypothesized that mononuclear phagocyte VGSCs are a target for monocyte/macrophage phenotypic switch, and liposome mediated inhibition of mononuclear phagocyte VGSC may attenuate myocardial ischemia/reperfusion (I/R) injury and improve post-infarction left ventricular remodeling.
Methodology/Principal Findings
Thin film dispersion method was used to prepare phenytoin (PHT, a non-selective VGSC inhibitor) entrapped liposomes. Pharmacokinetic study revealed that the distribution and elimination half-life of PHT entrapped liposomes were shorter than those of free PHT, indicating a rapid uptake by mononuclear phagocytes after intravenous injection. In rat peritoneal macrophages, several VGSC α subunits (NaV1.1, NaV1.3, NaV1.4, NaV1.5, NaV1.6, NaV1.7, NaVX, Scn1b, Scn3b and Scn4b) and β subunits were expressed at mRNA level, and PHT could suppress lipopolysaccharide induced M1 polarization (decreased TNF-α and CCL5 expression) and facilitate interleukin-4 induced M2 polarization (increased Arg1 and TGF-β1 expression). In vivo study using rat model of myocardial I/R injury, demonstrated that PHT entrapped liposome could partially suppress I/R injury induced CD43+ inflammatory monocyte expansion, along with decreased infarct size and left ventricular fibrosis. Transthoracic echocardiography and invasive hemodynamic analysis revealed that PHT entrapped liposome treatment could attenuate left ventricular structural and functional remodeling, as shown by increased ejection fraction, reduced end-systolic and end-diastolic volume, as well as an amelioration of left ventricular systolic (+dP/dtmax) and diastolic (-dP/dtmin) functions.
Conclusions/Significance
Our work for the first time demonstrates the therapeutic potential of VGSC antagonism via liposome mediated monocyte/macrophage targeting in acute phase after myocardial I/R injury. These results suggest that VGSCs in mononuclear phagocyte system might be a novel target for immunomodulation and treatment of myocardial I/R injury.
doi:10.1371/journal.pone.0074390
PMCID: PMC3777990  PMID: 24069305
21.  Screening for Voltage-Gated Sodium Channel Interacting Peptides 
Scientific Reports  2014;4:4569.
The voltage-gated sodium channel (VGSC) interacting peptide is of special interest for both basic research and pharmaceutical purposes. In this study, we established a yeast-two-hybrid based strategy to detect the interaction(s) between neurotoxic peptide and the extracellular region of VGSC. Using a previously reported neurotoxin JZTX-III as a model molecule, we demonstrated that the interactions between JZTX-III and the extracellular regions of its target hNav1.5 are detectable and the detected interactions are directly related to its activity. We further applied this strategy to the screening of VGSC interacting peptides. Using the extracellular region of hNav1.5 as the bait, we identified a novel sodium channel inhibitor SSCM-1 from a random peptide library. This peptide selectively inhibits hNav1.5 currents in the whole-cell patch clamp assays. This strategy might be used for the large scale screening for target-specific interacting peptides of VGSCs or other ion channels.
doi:10.1038/srep04569
PMCID: PMC3972499  PMID: 24691553
22.  Structural Basis for the Modulation of the Neuronal Voltage-Gated Sodium Channel NaV1.6 by Calmodulin 
Scientific Reports  2013;3:2435.
The neuronal-voltage gated sodium channel (VGSC), NaV1.6, plays an important role in propagating action potentials along myelinated axons. Calmodulin (CaM) is known to modulate the inactivation kinetics of NaV1.6 by interacting with its IQ motif. Here we report the crystal structure of apo-CaM:NaV1.6IQ motif, along with functional studies. The IQ motif of NaV1.6 adopts an α-helical conformation in its interaction with the C-lobe of CaM. CaM uses different residues to interact with NaV1.6IQ motif depending on the presence or absence of Ca2+. Three residues from NaV1.6, Arg1902, Tyr1904 and Arg1905 were identified as the key common interacting residues in both the presence and absence of Ca2+. Substitution of Arg1902 and Tyr1904 with alanine showed a reduced rate of NaV1.6 inactivation in electrophysiological experiments in vivo. Compared with other CaM:NaV complexes, our results reveal a different mode of interaction for CaM:NaV1.6 and provides structural insight into the isoform-specific modulation of VGSCs.
doi:10.1038/srep02435
PMCID: PMC3743062  PMID: 23942337
23.  A Novel Inhibitor of α9α10 Nicotinic Acetylcholine Receptors from Conus vexillum Delineates a New Conotoxin Superfamily 
PLoS ONE  2013;8(1):e54648.
Conotoxins (CTxs) selectively target a range of ion channels and receptors, making them widely used tools for probing nervous system function. Conotoxins have been previously grouped into superfamilies according to signal sequence and into families based on their cysteine framework and biological target. Here we describe the cloning and characterization of a new conotoxin, from Conus vexillum, named αB-conotoxin VxXXIVA. The peptide does not belong to any previously described conotoxin superfamily and its arrangement of Cys residues is unique among conopeptides. Moreover, in contrast to previously characterized conopeptide toxins, which are expressed initially as prepropeptide precursors with a signal sequence, a ‘‘pro’’ region, and the toxin-encoding region, the precursor sequence of αB-VxXXIVA lacks a ‘‘pro’’ region. The predicted 40-residue mature peptide, which contains four Cys, was synthesized in each of the three possible disulfide arrangements. Investigation of the mechanism of action of αB-VxXXIVA revealed that the peptide is a nicotinic acetylcholine receptor (nAChR) antagonist with greatest potency against the α9α10 subtype. 1H nuclear magnetic resonance (NMR) spectra indicated that all three αB-VxXXIVA isomers were poorly structured in aqueous solution. This was consistent with circular dichroism (CD) results which showed that the peptides were unstructured in buffer, but adopted partially helical conformations in aqueous trifluoroethanol (TFE) solution. The α9α10 nAChR is an important target for the development of analgesics and cancer chemotherapeutics, and αB-VxXXIVA represents a novel ligand with which to probe the structure and function of this protein.
doi:10.1371/journal.pone.0054648
PMCID: PMC3559828  PMID: 23382933
24.  The neonatal splice variant of Nav1.5 potentiates in vitro invasive behaviour of MDA-MB-231 human breast cancer cells 
Upregulation of functional voltage-gated Na+ channels (VGSCs) occurs in metastatic human breast cancer (BCa) in vitro and in vivo. The present study aimed to ascertain the specific involvement of the ‘neonatal’ splice variant of Nav1.5 (nNav1.5), thought to be predominant, in the VGSC-dependent invasive behaviour of MDA-MB-231 cells. Functional activity of nNav1.5 was suppressed by two different methods targeting nNav1.5: (i) small interfering RNA (siRNA), and (ii) a polyclonal antibody (NESO-pAb); effects upon migration and invasion were determined. nNav1.5 mRNA, protein and signalling were measured using real-time PCR, Western blotting, and patch clamp recording, respectively. Treatment with the siRNA rapidly reduced (by ~90 %) the level of nNav1.5 (but not adult Nav1.5) mRNA, but the protein reduction was much smaller (~30 %), even after 13 days. Nevertheless, the siRNA reduced peak VGSC current density by 33 %, and significantly increased the cells’ sensitivity to nanomolar tetrodotoxin (TTX). Importantly, the siRNA suppressed in vitro migration by 43 %, and eliminated the normally inhibitory effect of TTX. Migrated MDA-MB-231 cells expressed more nNav1.5 protein at the plasma membrane than non-migrated cells. Furthermore, NESO-pAb reduced migration by up to 42 %, in a dose-dependent manner. NESO-pAb also reduced Matrigel invasion without affecting proliferation. TTX had no effect on cells already treated with NESO-pAb. It was concluded that nNav1.5 is primarily responsible for the VGSC-dependent enhancement of invasive behaviour in MDA-MB-231 cells. Accordingly, targeting nNav1.5 expression/activity may be useful in clinical management of metastatic BCa.
doi:10.1007/s10549-006-9281-1
PMCID: PMC4122814  PMID: 16838113
Antibody; breast cancer; metastasis; RNAi; voltage-gated Na+ channel
25.  Pruning Nature: Biodiversity-Derived Discovery of Novel Sodium Channel Blocking Conotoxins from Conus bullatus 
Described herein is a general approach to identify novel compounds using the biodiversity of a megadiverse group of animals; specifically, the phylogenetic lineage of the venomous gastropods that belong to the genus Conus (“cone snails”). Cone snail biodiversity was exploited to identify three new μ-conotoxins, BuIIIA, BuIIIB and BuIIIC, encoded by the fish-hunting species Conus bullatus. BuIIIA, BuIIIB and BuIIIC are strikingly divergent in their amino acid composition compared to previous μ-conotoxins known to target the voltage-gated Na channel skeletal muscle subtype Nav1.4. Our preliminary results indicate that BuIIIB and BuIIIC are potent inhibitors of Nav1.4 (average block ~96%, at a 1 μM concentration of peptide), displaying a very slow off-rate not seen in previously characterized μ-conotoxins that block Nav1.4. In addition, the three new Conus bullatus μ-conopeptides help to define a new branch of the M-superfamily of conotoxins, namely M-5. The exogene strategy used to discover these Na channel-inhibiting peptides was based on both understanding the phylogeny of Conus, as well as the molecular genetics of venom μ-conotoxin peptides previously shown to generally target voltage-gated Na channels. The discovery of BuIIIA, BuIIIB and BuIIIC Na channel blockers expands the diversity of ligands useful in determining the structure-activity relationship of voltage-gated sodium channels.
doi:10.1016/j.toxicon.2008.10.017
PMCID: PMC2677393  PMID: 18950653
Biodiversity-derived compounds; Sodium channel ligands; exogenes

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