title: Differential phospholipid binding by site 3 and site 4 toxins. Implications for structural variability between voltage-sensitive sodium channel domains.
abstract: It has been shown recently that polypeptide toxins that modulate the gating properties of voltage-sensitive cation channels are able to bind to phospholipid membranes, leading to the suggestion that these toxins are able to access a channel-binding site that remains membrane-restricted (Lee, S.-Y., and MacKinnon, R. (2004) Nature 430, 232-235). We therefore examined the ability of anthopleurin B (ApB), a sea anemone toxin that selectively modifies inactivation kinetics of Na(V)1.x channels, and ProTx-II, a spider toxin that modifies activation kinetics of the same channels, to bind to liposomes. Whereas ProTx-II can be quantitatively depleted from solution upon incubation with phosphatidylcholine/phosphatidylserine liposomes, ApB displays no discernible phospholipid binding activity. We therefore examined the activities of structurally unrelated site 3 and site 4 toxins derived from Leiurus and Centruroides venoms, respectively, in the same assay. Like ApB, the site 3 toxin LqqV shows no lipid binding activity, whereas the site 4 toxin Centruroides toxin II, like ProTx-II, is completely bound. We conclude that toxins that modify inactivation kinetics via binding to Na(V)1.x site 3 lack the ability to bind phospholipids, whereas site 4 toxins, which modify activation, have this activity. This inherent difference suggests that the conformation of domain II more closely resembles that of the K(V)AP channel than does the conformation of domain IV.
authors.affiliation: Department of Biochemistry, School of Medicine and Biomedical Sciences, State University of New York, Buffalo, New York 14214, USA.
authors.forename: Jaime J
authors.initials: JJ
authors.lastname: Smith
authors.forename: Sujith
authors.initials: S
authors.lastname: Alphy
authors.forename: Anna L
authors.initials: AL
authors.lastname: Seibert
authors.forename: Kenneth M
authors.initials: KM
authors.lastname: Blumenthal
mesh_terms: D001665:Binding Sites; D002478:Cells, Cultured; D006801:Humans; D036341:Intercellular Signaling Peptides and Proteins; D009124:Muscle Proteins / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism; D062554:NAV1.5 Voltage-Gated Sodium Channel; D010455:Peptides / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism*; D024642:Potassium Channels, Voltage-Gated / Q000378:metabolism; D011487:Protein Conformation; D012604:Scorpion Venoms / Q000378:metabolism*; D015222:Sodium Channels / Q000737:chemistry* / Q000187:drug effects / Q000378:metabolism; D013111:Spider Venoms / Q000378:metabolism*
chemical_list: D036341:Intercellular Signaling Peptides and Proteins; D009124:Muscle Proteins; D062554:NAV1.5 Voltage-Gated Sodium Channel; D010455:Peptides; D010743:Phospholipids; D024642:Potassium Channels, Voltage-Gated; C470626:ProTx-II peptide; C568320:SCN5A protein, human; D012604:Scorpion Venoms; D015222:Sodium Channels; D013111:Spider Venoms; C072990:toxin 2, Centruroides noxius; C026132:anthopleurin B