The tarantula toxin ß/δ-TRTX-Pre1a highlights the importance of the S1-S2 voltage-sensor region for sodium channel subtype selectivity.

Voltage-gated sodium (NaV) channels are essential for the transmission of pain signals in humans making them prime targets for the development of new analgesics. Spider venoms are a rich source of peptide modulators useful to study ion channel structure and function. Here we describe ß/δ-TRTX-Pre1a, a 35-residue tarantula peptide that selectively interacts with neuronal NaV channels inhibiting peak current of hNaV1.1, rNaV1.2, hNaV1.6, and hNaV1.7 while concurrently inhibiting fast inactivation of hNaV1.1 and rNaV1.3. The DII and DIV S3-S4 loops of NaV channel voltage sensors are important for the interaction of Pre1a with NaV channels but cannot account for its unique subtype selectivity. Through analysis of the binding regions we ascertained that the variability of the S1-S2 loops between NaV channels contributes substantially to the selectivity profile observed for Pre1a, particularly with regards to fast inactivation. A serine residue on the DIV S2 helix was found to be sufficient to explain Pre1a's potent and selective inhibitory effect on the fast inactivation process of NaV1.1 and 1.3. This work highlights that interactions with both S1-S2 and S3-S4 of NaV channels may be necessary for functional modulation, and that targeting the diverse S1-S2 region within voltage-sensing domains provides an avenue to develop subtype selective tools.

Synthesis, pharmacology, and biostructural characterization of novel α4ß2 nicotinic acetylcholine receptor agonists.

In our search for selective agonists for the α(4)ß(2) subtype of the nicotinic acetylcholine receptors (nAChRs), we have synthesized and characterized a series of novel heterocyclic analogues of 3-(dimethylamino)butyl dimethylcarbamate (DMABC, 4). All new heterocyclic analogues, especially N,N-dimethyl-4-(1-methyl-1H-imidazol-2-yloxy)butan-2-amine (7), showed an improved binding selectivity profile in favor of α(4)ß(2) over other nAChR subtypes, primarily due to impaired binding at ß(4) containing receptors. This observation can be rationalized based on cocrystal structures of (R)-4 and (R)-7 bound to acetylcholine binding protein from Lymnaea stagnalis. Functional characterization at both (α(4))(2)(ß(2))(3) and (α(4))(3)(ß(2))(2) receptors using two-electrode voltage clamp techniques in Xenopus laevis oocytes indicates that the investigated compounds interact differently with the two receptor stoichiometries. Compound 7 is an efficacious agonist at both α(4)-ß(2) and α(4)-α(4) binding sites, while the close analogue N,N-dimethyl-4-(1,4-dimethyl-1H-imidazol-2-yloxy)butan-2-amine (9) primarily activates via α(4)-ß(2) binding sites. The results suggest that it may be possible to rationally design compounds with specific stoichiometry preferences.