title: PnTx4-3, a new insect toxin from Phoneutria nigriventer venom elicits the glutamate uptake inhibition exhibited by PhTx4 toxic fraction.
abstract: Several pools of neurotoxic peptides obtained from fractionated Phoneutria nigriventer venom induce different toxicological effects. One of them, PhTx4, is highly toxic towards insects and displays only a slight toxicity when injected in mice. Also, this fraction contains a class of peptides that are able to inhibit glutamate uptake in preparations of mammalian central nervous systems (CNS). In this work a new toxin called PnTx4-3 was isolated from the PhTx4 fraction by reverse phase and anion exchange steps using high performance liquid chromatography (HPLC). Edman sequencing of PnTx4-3 revealed that it was a polypeptide of 48 amino acid residues, containing 10 cysteines cross-linked by five disulfide bridges. The molecular mass measured by ES-Q-TOF mass spectrometry was 5199.49+/-0.64 Da, which is very close to the calculated mass from amino acid sequence (5199.99 Da). This toxin induces immediate excitatory effects when injected intrathoracically in house flies and cockroaches. Intracerebroventricular injections of 30 microg of PnTx4-3 in mice resulted in no apparent signs of intoxication. In order to make an orthologous comparison, pharmacological characterisation were carried out in rat brain synaptosomes by using [3H]-L-glutamate, showed that the whole PhTx4 fraction as well as the pure toxins PnTx4-3, Tx4(6-1) and Tx4(5-5) obtained of this fraction, were able to inhibit the glutamate uptake in the micromolar concentration range. PnTx4-3 inhibits the glutamate uptake in a dose dependent manner, with an IC50 of approximately 1 microM. PnTx4-3 is highly homologous to the Tx4(6-1) and Tx4(5-5) toxins previously described from the same fraction.
authors.affiliation: Departamento de Fisiologia e Farmacologia, Instituto de Ciencias Biologicas, UFMG Av. Antônio Carlos, 6627-Pampulha Caixa Postal 486-31270-901, Belo Horizonte, MG, Brazil.
authors.forename: Leida Calegário
authors.initials: LC
authors.lastname: Oliveira
authors.forename: Maria Elena
authors.initials: ME
authors.lastname: De Lima
authors.forename: Adriano M C
authors.initials: AM
authors.lastname: Pimenta
authors.forename: Pascal
authors.initials: P
authors.lastname: Mansuelle
authors.forename: Hervé
authors.initials: H
authors.lastname: Rochat
authors.forename: Marta N
authors.initials: MN
authors.lastname: Cordeiro
authors.forename: Michael
authors.initials: M
authors.lastname: Richardson
authors.forename: Suely G
authors.initials: SG
authors.lastname: Figueiredo
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism; D004175:Diptera; D018698:Glutamic Acid / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D051379:Mice; D008969:Molecular Sequence Data; D009479:Neuropeptides / Q000737:chemistry / Q000633:toxicity*; D009498:Neurotoxins / Q000737:chemistry / Q000633:toxicity*; D051381:Rats; D017208:Rats, Wistar; D013111:Spider Venoms / Q000737:chemistry / Q000633:toxicity*; D013112:Spiders
chemical_list: D009479:Neuropeptides; D009498:Neurotoxins; C482175:PnTx4-3; D013111:Spider Venoms; D018698:Glutamic Acid