|Importance of position 8 in μ-conotoxin KIIIA for voltage-gated sodium channel selectivity|Van Der Haegen, A.; Peigneur, S.; Tytgat, J. (2011). Importance of position 8 in μ-conotoxin KIIIA for voltage-gated sodium channel selectivity. The FEBS Journal 278(18): 3408-3418. dx.doi.org/10.1111/j.1742-4658.2011.08264.x
In: The FEBS Journal. Wiley-Blackwell: Oxford. ISSN 1742-464X, more
Conus kinoshitai; electrophysiology; KIIIA; sodium channels;mu-conotoxins
μ-conotoxin KIIIA from Conus kinoshitai is a 16-residue peptide that acts as a potent pore blocker of several voltage-gated sodium channels (Nav). In order to obtain more selective blockers and to investigate the role of Trp at position 8, we substituted this residue with Arg, Gln and Glu. KIIIA and analogues were tested on a range of Nav expressed in Xenopus laevis oocytes. The rank order of potency for KIIIA was: rNav1.4 ≥ rNav1.2 > mNav1.6 > rNav1.3, with IC50 values of 48 ± 6 nm, 61 ± 5 nm, 183 ± 31 nm and 3.6 ± 0.3 μm, respectively, whereas no effect was seen on hNav1.5 and hNav1.8 at a concentration of 10 μm. Replacement of Trp8 resulted in more selective blockers with a preference for neuronal sodium channels over the skeletal sodium channel. The activity on rNav1.4 was reduced about 40-, 70- and 200-fold for [W8R]KIIIA, [W8Q]KIIIA and [W8E]KIIIA, respectively. All analogues showed a completely reversible block of rNav1.2, as opposed to the partial reversibility of KIIIA. At saturating concentrations, complete block of rNav1.2 was never achieved. The residual current was lower than 10%, except for [W8E]KIIIA. KIIIA had no effect on the voltage dependence of activation of rNav1.2, whereas all analogues caused a depolarizing shift. Overall, this study shows that Trp8 is a key residue in the pharmacophore. Replacement of Trp8 enables more selective blockers to be obtained for neuronal sodium channels. Trp is a key determinant for the reversibility of block of rNav1.2.