title: Structure and activity analysis of two spider toxins that alter sodium channel inactivation kinetics.
abstract: In this work, Phoneutria nigriventer toxins PnTx2-5 and PnTx2-6 were shown to markedly delay the fast inactivation kinetics of neuronal-type sodium channels. Furthermore, our data show that they have significant differences in their interaction with the channel. PnTx2-6 has an affinity 6 times higher than that of PnTx2-5, and its effects are not reversible within 10-15 min of washing. PnTx2-6 partially (59%) competes with the scorpion alpha-toxin AaHII, but not with the scorpion beta-toxin CssIV, thus suggesting a mode of action similar to that of site 3 toxins. However, PnTx2-6 is not removed by strong depolarizing pulses, as in the known site 3 toxins. We have also established the correct PnTx2-5 amino acid sequence and confirmed the sequence of PnTx2-6, in both cases establishing that the cysteines are in their oxidized form. A structural model of each toxin is proposed. They show structures with poor alpha-helix content. The model is supported by experimental and theoretical tests. A likely binding region on PnTx2-5 and PnTx2-6 is proposed on the basis of their different affinities and sequence differences.
authors.affiliation: Department of Biochemistry and Immunology, Instituto de Ciências Biológicas, Universidade Federal de Minas Gerais, Belo Horizonte, MG, Brazil.
authors.forename: Alessandra
authors.initials: A
authors.lastname: Matavel
authors.forename: Cécile
authors.initials: C
authors.lastname: Fleury
authors.forename: Leida C
authors.initials: LC
authors.lastname: Oliveira
authors.forename: Franck
authors.initials: F
authors.lastname: Molina
authors.forename: Maria Elena
authors.initials: ME
authors.lastname: de Lima
authors.forename: Jader S
authors.initials: JS
authors.lastname: Cruz
authors.forename: Marta N
authors.initials: MN
authors.lastname: Cordeiro
authors.forename: Michael
authors.initials: M
authors.lastname: Richardson
authors.forename: Carlos H I
authors.initials: CH
authors.lastname: Ramos
authors.forename: Paulo S L
authors.initials: PS
authors.lastname: Beirão
mesh_terms: D007700:Kinetics; D008958:Models, Molecular; D009479:Neuropeptides / Q000737:chemistry / Q000494:pharmacology; D010455:Peptides / Q000737:chemistry / Q000494:pharmacology*; D011485:Protein Binding; D011487:Protein Conformation; D012604:Scorpion Venoms; D015222:Sodium Channels / Q000187:drug effects* / Q000378:metabolism; D013111:Spider Venoms / Q000737:chemistry / Q000494:pharmacology*; D013329:Structure-Activity Relationship
chemical_list: D009479:Neuropeptides; D010455:Peptides; D012604:Scorpion Venoms; D015222:Sodium Channels; D013111:Spider Venoms; C540366:Tx2-5 protein, Phoneutria nigriventer; C540367:Tx2-6 protein, Phoneutria nigriventer