A homology model of the housefly voltage-gated sodium channel was developed to predict the location of binding sites for the insecticides fenvalerate, a synthetic pyrethroid, and DDT an early generation organochlorine. The model successfully addresses the state-dependent affinity of pyrethroid insecticides, their mechanism of action and the role of mutations in the channel that are known to confer insecticide resistance. The sodium channel was modelled in an open conformation with the insecticide-binding site located in a hydrophobic cavity delimited by the domain II S4-S5 linker and the IIS5 and IIIS6 helices. The binding cavity is predicted to be accessible to the lipid bilayer and therefore to lipid-soluble insecticides. The binding of insecticides and the consequent formation of binding contacts across different channel elements could stabilize the channel when in an open state, which is consistent with the prolonged sodium tail currents induced by pyrethroids and DDT. In the closed state, the predicted alternative positioning of the domain II S4-S5 linker would result in disruption of pyrethroid-binding contacts, consistent with the observation that pyrethroids have their highest affinity for the open channel. The model also predicts a key role for the IIS5 and IIIS6 helices in insecticide binding. Some of the residues on the helices that form the putative binding contacts are not conserved between arthropod and non-arthropod species, which is consistent with their contribution to insecticide species selectivity. Additional binding contacts on the II S4-S5 linker can explain the higher potency of pyrethroid insecticides compared with DDT.

Mutations in the DIIS4-S5 linker and DIIS5 have identified hotspots of pyrethroid and DDT interaction with the Drosophila para sodium channel. Wild-type and mutant channels were expressed in Xenopus oocytes and subjected to voltageclamp analysis. Substitutions L914I, M918T, L925I, T929I and C933A decreased deltamethrin potency, M918T, L925I and T929I decreased permethrin potency and T929I, L925I and I936V decreased fenfluthrin potency. DDT potency was unaffected by M918T, but abolished by T929I and reduced by L925I, L932F and I936V, suggesting that DIIS5 contains at least part of the DDT binding domain. The data support a computer model of pyrethroid and DDT binding.

Chronic pain often represents a severe, debilitating condition. Up to 10% of the worldwide population are affected, and many patients are poorly responsive to current treatment strategies. Nociceptors detect noxious conditions to produce the sensation of pain, and this signal is conveyed to the CNS by means of action potentials. The fast upstroke of action potentials is mediated by voltage-gated sodium channels, of which nine pore-forming alpha-subunits (Nav1.1-1.9) have been identified. Heterogeneous functional properties and distinct expression patterns denote specialized functions of each subunit. The Nav1.7 and Nav1.8 subunits have emerged as key molecules involved in peripheral pain processing and in the development of an increased pain sensitivity associated with inflammation and tissue injury. Several mutations in the SCN9A gene encoding for Nav1.7 have been identified as important cellular substrates for different heritable pain syndromes. This review aims to cover recent progress on our understanding of how biophysical properties of mutant Nav1.7 translate into an aberrant electrogenesis of nociceptors. We also recapitulate the role of Nav1.8 for peripheral pain processing and of additional sodium channelopathies which have been linked to disorders with pain as a significant component.

The Anopheles gambiae 1000 Genomes Consortium †This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Extramembranous domains play important roles in the structure and function of membrane proteins, contributing to protein stability, forming association domains, and binding ancillary subunits and ligands. However, these domains are generally flexible, making them difficult or unsuitable targets for obtaining highresolution X-ray and NMR structural information. In this study we show that the highly sensitive method of synchrotron radiation circular dichroism (SRCD) spectroscopy can be used as a powerful tool to investigate the structure of the extramembranous C-terminal domain (CTD) of the prokaryotic voltage-gated sodium channel (Na V ) from Bacillus halodurans, NaChBac. Sequence analyses predict its CTD will consist of an unordered region followed by an α-helix, which has a propensity to form a multimeric coiled-coil motif, and which could form an association domain in the homotetrameric NaChBac channel. By creating a number of shortened constructs we have shown experimentally that the CTD does indeed contain a stretch of ∼20 α-helical residues preceded by a nonhelical region adjacent to the final transmembrane segment and that the efficiency of assembly of channels in the membrane progressively decreases as the CTD residues are removed. Analyses of the CTDs of 32 putative prokaryotic Na V sequences suggest that a CTD helical bundle is a structural feature conserved throughout the bacterial sodium channel family.membrane protein assembly | membrane protein structure | synchrotron radiation circular dichroism (SRCD) spectroscopy | voltage-gated sodium channel | secondary structure S odium, calcium, and potassium channels form a family of integral membrane proteins that selectively regulate ion conductance across an otherwise impermeable lipid membrane. In eukaryotic voltage-gated sodium and calcium channels the functional unit is formed by assembly of four homologous domains of a single polypeptide chain. Each domain is composed of six transmembrane (TM) helices, with the four N-terminal helices forming the voltage-sensing subdomain and the two C-terminal helices comprising the pore subdomain. In contrast, in both eukaryotic and prokaryotic potassium channels the functional unit is a homo-tetramer formed from identical monomers that each correspond to one of the sodium or calcium channel domains (1). The crystal structures of a number of potassium channels have been determined (2-4), which have confirmed the tetrameric nature of the channels and details of their transmembrane (TM) regions. The structures of the extramembranous C-terminal domains of most of these channels, however, were not defined in the crystal structures, either because they had been removed after assembly (KcsA) (2) in order to improve crystallization, or because they were disordered in the crystal (KvAP and MlotiK1) (3, 4).The extramembranous termini of potassium channels appear to play important roles in channel assembly, primarily as tetramerization domains. Examples include the N-terminal T1 domain of Shaker channels (5) and C-terminal do...