Phospholipid binding activity of the spider venom peptides ProTx-I and ProTx-II

E. Deplazes,^1,2,3 S.T. Henriques,³ N. Lawrence,³ G.F. King,³ A.E. Mark,^2,3 D.J. Craik³ and C.I. Schroeder,³ ¹School of Biomedical Sciences, Curtin University, Perth, WA 6109, Australia, ²School of Chemistry & Molecular Biosciences, The University of Queensland, St Lucia, QLD 4072, Australia and ³Institute for Molecular Bioscience, The University of Queensland, St Lucia, QLD 4072, Australia.

ProTx-I and ProTx-II are disulfide-rich, amphipathic peptides isolated from tarantula venom. They are able to inhibit the human voltage-gated sodium channel 1.7 (hNa_V1.7), a channel involved in pain sensation, and are thus promising lead molecules for the development of new analgesics. Both ProTx-I and ProTx-II inhibit the channel by binding to the membrane-embedded voltage sensor domain. However, the membrane-binding properties and its the importance in the inhibition of hNa_V1.7 by ProTx-I and ProTx-II remain poorly understood. In this study we examined the membrane-binding activities of ProTx-I and ProTx-II and analogues using unrestrained molecular dynamics (MD) simulations combined with surface plasmon resonance (SPR) and fluorescence spectroscopy experiments (Deplazes et al., 2016; Henriques et al., 2016).

Results from SPR experiments indicate that both ProTx-I and ProTx-II bind to neutral and anionic phospholipid bilayers with a preference for membranes that contain anionic lipids. The fluorescence spectroscopy experiments and MD simulations showed that the peptides do not partition into the hydrophobic core of the lipid bilayer but remain at the water-lipid interface when bound to the membrane. Results from MD simulations also revealed that both peptides exhibit a distinct lipid-interaction surface composed of a number of residues on or near the hydrophobic face of the peptides. Despite limited sequence identity (26%) between ProTx-I and ProTx-II the lipid-interaction surface of both peptides is dominated by Trp. This is consistent with the significantly reduced membrane-binding activity of [Trp/Tyr] mutants of ProTx-II. The combined data support a model whereby a hydrophobic patch on the peptide surface anchors the molecule at the cell surface.

Deplazes E, Henriques ST, Smith JJ, King GF, Craik DJ, Mark AE, Schroeder CI. (2016) BBA Biomembranes 1858: 872-82.

Henriques ST, Deplazes E, Lawrence N, Cheneval O, Chaousis S, Inserra M, Thongyoo P, King GF, Mark AE, Vetter I, Craik DJ, Schroeder CI. (2016) J Biol Chem 291: 17049-65.