Molecular determinants of transport stimulation of EAAT2 are located at interface between the trimerization and substrate transport domains

Excitatory amino acid transporters (EAATs) regulate glutamatergic signal transmission by clearing extracellular glutamate. Dysfunction of these transporters has been implicated in the pathogenesis of various neurological disorders. Previous studies have shown that venom from the spider Parawixia bistriata and a purified compound (Parawixin1) stimulate EAAT2 activity and protect retinal tissue from ischemic damage. In the present study, the EAAT2 subtype specificity of this compound was explored, employing chimeric proteins between EAAT2 and EAAT3 transporter subtypes and mutants to characterize the structural region targeted by the compound. This identified a critical residue (Histidine-71 in EAAT2 and Serine-45 in EAAT3) in transmembrane domain 2 (TM2) to be important for the selectivity between EAAT2 and EAAT3 and for the activity of the venom. Using the identified residue in TM2 as a structural anchor, several neighboring amino acids within TM5 and TM8 were identified to also be important for the activity of the venom. This structural domain of the transporter lies at the interface of the rigid trimerization domain and the central substrate-binding transport domain. Our studies suggest that the mechanism of glutamate transport enhancement involves an interaction with the transporter that facilitates the movement of the transport domain. We identified a domain (purple star) in the glutamate transporter EAAT2 that is important for transport stimulation through a spider venom, and suggest a mechanism for enhanced transporter function through facilitated substrate translocation (arrow). Because the dysfunction of glutamate transporters is implicated in the pathogenesis of neurological disorders, understanding the mechanisms of enhanced transport could have therapeutic implications

Effects of the crude venom and two fractions isolated from the solitary spider Scaptocosa raptoria on gamma-aminobutyric acid and glutamate uptake in synaptosomes from rat cerebral cortex

USP, FFCLRP, Dept Biol, Ribeirao Preto, BrazilUSP, FMRP, Dept Biochem, Ribeirao Preto, BrazilUNIFESP, Dept Biophys, Sao Paulo, BrazilUSP, FFCLRP, Dept Math, Ribeirao Preto, BrazilUNIFESP, Dept Biophys, Sao Paulo, BrazilWeb of Scienc

Characterization of the actions of AvTx 7 isolated from Agelaia vicina (Hymenoptera : Vespidae) wasp venom on synaptosomal glutamate uptake and release

It has previously been shown that the denatured crude extract of Agelaia vicina wasp venom inhibits glutamate and GABA uptake in rat cerebral cortex synaptosomes. To identify the components responsible for these effects, the neurotoxin AvTx 7 (molecular weight of 1210 Da) was isolated from A. vicina venom and its effects on glutamate neurotransmission investigated. AvTx 7 inhibits glutamate uptake in a dose-dependent and uncompetitive manner. AvTx 7 was found to stimulate the glutamate release in the presence of calcium and sodium channel blockers, suggesting that its action is not mediated through these channels. AvTx 7 potentiates glutamate release in the presence of K+ channel blockers tetraethylammoniurn and 4-aminopyridine, indicating that the toxin may act through these drugs-sensible K+ channels. We suggest that AvTx 7 can be a valuable tool to enhance our understanding of K+ channels' involvement in the release of glutamate. (C) 2004 Wiley Periodicals, Inc.Univ São Paulo, Fac Philosophy Sci & Literature, Lab Neurobiol & Venoms, Ribeirao Preto, SP, BrazilUniv São Paulo, Sch Med, Lab Neurobiol & Venoms, Neurochem Lab, Ribeirao Preto, SP, BrazilOregon Hlth Sci Univ, Vollum Inst, Portland, OR 97201 USAUniversidade Federal de São Paulo, Dept Biophys, São Paulo, SP, BrazilUniversidade Federal de São Paulo, Dept Biophys, São Paulo, SP, BrazilWeb of Scienc

Anticonvulsant and GABA uptake inhibition properties of venom fractions from the spiders Parawixia bistriata and Scaptocosa raptoria

In this article we describe an in vivo anticonvulsant effect from denatured crude venom and partially isolated fractions from two spiders: Parawixia bistriata and Scaptocosa raptoria. Intracerebroventricular injections of these venoms and fractions abolished rat convulsive tonic-clonic seizures induced by picrotoxin, bicuculline and pentylenetetrazole, and also, inhibited GABA uptake in synaptosomes of rat cerebral cortex. the venoms described in this work seems to be promising tools for the study of the GABAergic system, and may be a potential source for new anticonvulsant drugs.Univ São Paulo, Lab Neurobiol & Peconhas, Dept Biol, Fac Filosofia,Ciencias & Letras Ribeirao Preto, BR-14049901 São Paulo, BrazilUniv São Paulo, Fac Med Ribeirao Preto, Lab Neuroquim, Dept Bioquim, BR-14049901 São Paulo, BrazilUniversidade Federal de São Paulo, Dept Biofis, São Paulo, BrazilUniversidade Federal de São Paulo, Dept Biofis, São Paulo, BrazilWeb of Scienc

Superficial distribution of aromatic compounds and geomicrobiology of sediments from Suruí Mangrove, Guanabara Bay, RJ, Brazil

The distribution of selected aromatic compounds and microbiology were assessed in superficial sediments from Suruí Mangrove, Guanabara Bay. Samples were collected at 23 stations, and particle size, organic matter, aromatic compounds, microbiology activity, biopolymers, and topography were determined. The concentration of aromatic compounds was distributed in patches over the entire mangrove, and their highest total concentration was determinated in the mangrove's central area. Particle size differed from most mangroves in that Suruí Mangrove has chernies on the edges and in front of the mangrove, and sand across the whole surface, which hampers the relationship between particle size and hydrocarbons. An average @ 10% p/p of organic matter was obtained, and biopolymers presented high concentrations, especially in the central and back areas of the mangrove. The biopolymers were distributed in high concentrations. The presence of fine sediments is an important factor in hydrocarbon accumulation. With high concentration of organic matter and biopolymers, and the topography with chernies and roots protecting the mangrove, calmer areas are created with the deposition of material transported by wave action. Compared to global distributions, concentrations of aromatic compounds in Suruí Mangrove may be classified from moderate to high, showing that the studied area is highly impacted