Abstract
μ-Conotoxins are potent and highly specific peptide blockers of voltage-gated sodium channels. In this study, the solution structure of μ-conotoxin GIIIC was determined using 2D NMR spectroscopy and simulated annealing calculations. Despite high sequence similarity, GIIIC adopts a three-dimensional structure that differs from the previously observed conformation of μ-conotoxins GIIIA and GIIIB due to the presence of a bulky, non-polar leucine residue at position 18. The side chain of L18 is oriented towards the core of the molecule and consequently the N-terminus is re-modeled and located closer to L18. The functional characterization of GIIIC defines it as a canonical μ-conotoxin that displays substantial selectivity towards skeletal muscle sodium channels (NaV), albeit with ~2.5-fold lower potency than GIIIA. GIIIC exhibited a lower potency of inhibition of NaV1.4 channels, but the same NaV selectivity profile when compared to GIIIA. These observations suggest that single amino acid differences that significantly affect the structure of the peptide do in fact alter its functional properties. Our work highlights the importance of structural factors, beyond the disulfide pattern and electrostatic interactions, in the understanding of the functional properties of bioactive peptides. The latter thus needs to be considered when designing analogues for further applications.
Highlights
Voltage-gated sodium channels (VGSCs or NaV ) are responsible for the influx of sodium ions during action potentials in excitable cells [1]
Results conformation of the N-terminus in GIIIC, that may contribute to its high selectivity for the NaV1.4 subtype when compared to GIIIA and GIIIB in radioligand displacement studies [18,24]
GIIIC and GIIIA were chemically synthesized by automated solid phase peptide synthesis which afforded2.1
Summary
Voltage-gated sodium channels (VGSCs or NaV ) are responsible for the influx of sodium ions during action potentials in excitable cells [1]. The μ-conotoxin binding site on VGSCs partially overlaps that of the classical sodium channel inhibitors, tetrodotoxin (TTX) and saxitoxin (STX), and the blocking. One of the best characterised μ-conotoxins is the 22 amino acid peptide GIIIA from Conus. One of the best characterised μ-conotoxins is the 22 amino acid peptide GIIIA from Conus geographus [4,9,10,11,12]. This conotoxin potently targets the skeletal muscle subtype NaV 1.4 (IC50 : 19 nM), geographus [4,9,10,11,12].
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