Structures of μO-conotoxins from Conus marmoreus

Abstract

The O-conotoxins are an intriguing class of conotoxins targeting various voltage-dependent sodium channels and molluscan calcium channels. In the current study, we have shown MrVIA and MrVIB to be the first known peptidic inhibitors of the transient tetrodotoxinresistant (TTX-R) Na ؉ current in rat dorsal root ganglion neurons, in addition to inhibiting tetrodotoxinsensitive Na ؉ currents. Human TTX-R sodium channels are a therapeutic target for indications such as pain, highlighting the importance of the O-conotoxins as potential leads for drug development. Furthermore, we have used NMR spectroscopy to provide the first structural information on this class of conotoxins. MrVIA and MrVIB are hydrophobic peptides that aggregate in aqueous solution but were solubilized in 50% acetonitrile/water. The three-dimensional structure of MrVIB consists of a small ␤-sheet and a cystine knot arrangement of the three-disulfide bonds. It contains four backbone "loops" between successive cysteine residues that are exposed to the solvent to varying degrees. The largest of these, loop 2, is the most disordered part of the molecule, most likely due to flexibility in solution. This disorder is the most striking difference between the structures of MrVIB and the known ␦-and -conotoxins, which along with the O-conotoxins are members of the O superfamily. Loop 2 of -conotoxins has previously been shown to contain residues critical for binding to voltage-gated calcium channels, and it is interesting to speculate that the flexibility observed in MrVIB may accommodate binding to both sodium and molluscan calcium channels.

μO-conotoxin MrVIB selectively blocks Na v 1.8 sensory neuron specific sodium channels and chronic pain behavior without motor deficits

“…The absence of Na v 1.4 in the CNS and the ability of MrVIB to inhibit only certain pain types after intraplantar injection argue against an involvement of Na v 1.4 in the reduction in pain behavior produced by MrVIB. The analgesic effect of MrVIB is also not expected to involve inhibition of voltage-gated calcium channels, because we have demonstrated that the isotoxin MrVIA is without effect on calcium currents in rat sensory neurons (14). The presence of normal neuropathic pain in Na v 1.8 or Na v 1.7͞Na v 1.8-knockout mice indicates that TTX-S channels (and other channels) are able to contribute to a greater or lesser extent to altered levels of neuronal excitability (30).…”

“…After screening crude venoms from Ϸ30 species, we identified two closely related conotoxins, O-conotoxin MrVIA and O-conotoxin MrVIB (MrVIB), which selectively inhibited the tetrodotoxin-resistant (TTX-R) sodium current without affecting calcium current in sensory neurons (14). Here, we determine the VGSC subtypeselectivity of MrVIB in rat sensory neurons and heterologous expression systems and establish its selectivity for pain pathways in rat models of persistent pain.…”

Conopressin-T from Conus tulipa Reveals an Antagonist Switch in Vasopressin-like Peptides

“…Spectra were recorded at 290 K on a Bruker AVANCE-600 spectrometer. Two-dimensional NMR spectra were recorded in phase-sensitive mode using time-proportional phase incrementation for quadrature detection in the t1 dimension (19,20). The two-dimensional experiments consisted of a TOCSY using a MLEV-17 spin lock sequence with a mixing time of 80 ms, DQF-COSY, and NOESY with mixing times of 200 -300 ms. Solvent suppression was achieved using a modified WATERGATE sequence.…”

“…The starting structures were generated using random ( , ) dihedral angles and energy-minimized to produce structures with the correct local geometry. A set of 50 structures was generated by a torsion angle simulated annealing protocol (19,20). This protocol involved a high temperature phase comprising 4000 steps of 0.015 ps of torsion angle dynamics, a cooling phase with 4000 steps of 0.015 ps of torsion angle dynamics during which the temperature was lowered to 0 K, and finally an energy minimization phase comprising 500 steps of Powell minimization.…”

Conotoxins: from the biodiversity of gastropods to new drugs

“…mО-Конотоксины mО-MrVIA и mО-MrVIB способны ингибировать потенциалзависимые натриевые каналы нейронов моллюсков, амфибий [66] и млекопитающих [44,[66][67][68][69][70]. Эти токсины ингибируют ТТХ-устойчивые натриевые каналы Nav.8 нейронов крысы значительно эффективнее, чем ТТХ-чувствительные [67,68].…”