Search

Voltage-gated potassium channels (VGKCs) comprise the largest and most complex families of ion channels. Approximately 70 genes encode VGKC alpha subunits, which assemble into functional tetrameric channel complexes. These subunits can also combine to form heteromeric channels, significantly expanding the potential diversity of VGKCs. The functional expression and physiological role of heteromeric K-channels have remained largely unexplored due to the lack of tools to probe their functions. Conotoxins, from predatory cone snails, have high affinity and specificity for heteromeric combinations of K-channels and show great promise for defining their physiological roles. In this work, using conotoxin kM-RIIIJ as a pharmacological probe, we explore the expression and physiological functions of heteromeric Kv1.2 channels using constellation pharmacology platform. We report that heteromers of Kv1.2/1.1 are highly expressed in proprioceptive neurons found in the dorsal root ganglion (DRG). Inhibition of Kv1.2/1.1 heteromers leads to an influx of calcium ions, suggesting that these channels regulate neuronal excitability. We also present evidence that Kv1.2/1.1 heteromers counteract persistent sodium currents, and that inhibiting these channels leads to tonic firing of action potentials. Additionally, kM-RIIIJ impaired proprioception in mice, uncovering a previously unrecognized physiological function of heteromeric Kv1.2/1.1 channels in proprioceptive sensory neurons of the DRG. [ABSTRACT FROM AUTHOR]

A novel paralytic peptide with 32 AA and a single disulfide bond purified from the venom of Conus parius, a fish-hunting species designated as [alpha]C-conotoxin PrXA with similar biochemical features as found in snake toxins known as Waglerins is reported.

Newly identified alphaA(sub s)-conotoxins was characterized from Conus pergrandis and a detailed characterization of alphaA-conotoxins was reported. The characterization of short alphaA-conotoxins revealed diverse kinetics of a block of the fetal muscle mammalian neuromuscular nicotinic acetylcholine receptor, particularly in dissociation rates.

The characterization of a 24 AA conantokin from Conus brettinghami, the first conantokin that does not have the conserved glutamate residue at position 2 is reported. The results revealed that systematic definition of key determinants in the conantokin peptides for NMDA receptor subtype selectivity is an essential component in the development of conantokin peptides that are highly selective for each specific NMDA receptor subtype.

The purification and characterization of a novel peptide from the venom of Conus radiatus with the same Cys pattern as sigma-conotoxin GVIIIA (sigma-GVIIIA) which diverges in its primary amino acid sequence, post-translational modification, and molecular targets are described. This peptide defines a new family of conotoxins within the S superfamily namely the alphaS family of conotoxins.

The vast complexity of native heteromeric K+ channels is largely unexplored. Defining the composition and subunit arrangement of individual subunits in native heteromeric K+ channels and establishing their physiological roles is experimentally challenging. Here we systematically explored this "zone of ignorance" in molecular neuroscience. Venom components, such as peptide toxins, appear to have evolved to modulate physiologically relevant targets by discriminating among closely related native ion channel complexes. We provide proof-of-principle for this assertion by demonstrating that κM-conotoxin RIIIJ (κM-RIIIJ) from Conus radiatus precisely targets "asymmetric" Kv channels composed of three Kv1.2 subunits and one Kv1.1 or Kv1.6 subunit with 100-fold higher apparent affinity compared with homomeric Kv1.2 channels. Our study shows that dorsal root ganglion (DRG) neurons contain at least two major functional Kv1.2 channel complexes: a heteromer, for which κM-RIIIJ has high affinity, and a putative Kv1.2 homomer, toward which κM-RIIIJ is less potent. This conclusion was reached by (i) covalent linkage of members of the mammalian Shaker-related Kv1 family to Kv1.2 and systematic assessment of the potency of κM-RIIIJ block of heteromeric K+ channel-mediated currents in heterologous expression systems; (ii) molecular dynamics simulations of asymmetric Kv1 channels providing insights into the molecular basis of κM-RIIIJ selectivity and potency toward its targets; and (iii) evaluation of calcium responses of a defined population of DRG neurons to κM-RIIIJ. Our study demonstrates that bioactive molecules present in venoms provide essential pharmacological tools that systematically target specific heteromeric Kv channel complexes that operate in native tissues. [ABSTRACT FROM AUTHOR]

Interactions between animals have been investigated primarily through the direct observations of field biologists. But a complementary approach is emerging from an entirely different sector of biology: characterization of molecules [...]

It has been shown previously in a number of systems that after an extended block of activity, synaptic strength is increased. We found that an extended block of synaptic activity at the mouse neuromuscular junction, using a tetrodotoxin cuff in vivo, increased synaptic strength by prolonging the evoked endplate current (EPC) decay. Prolongation of EPC decay was accompanied by only modest prolongation of spontaneous miniature EPC (MEPC) decay. Prolongation of EPC decay was reversed when quantal content was lowered by reducing extracellular calcium. These findings suggested that the cause of EPC prolongation was presynaptic in origin. However, when we acutely inhibited fetal-type acetylcholine receptors (AChRs) using a novel peptide toxin (αA-conotoxin OIVA[K15N]), prolongation of both EPC and MEPC decay were reversed. We also blocked synaptic activity in a mutant strain of mice in which persistent muscle activity prevents upregulation of fetal-type AChRs. In these mice, there was no prolongation of EPC decay. We conclude that upregulation of fetal-type AChRs after blocking synaptic activity causes modest prolongation of MEPC decay that is accompanied by much greater prolongation of EPC decay. This might occur if acetylcholine escapes from endplates and binds to extrajunctional fetal-type AChRs only during large, evoked EPCs. Our study is the first to demonstrate a functional role for upregulation of extrajunctional AChRs. [ABSTRACT FROM AUTHOR]