Characterization of Glutamate Receptor by Spider Toxin

Abstract

Recent study has shown that the venom of some orb-web spiders contain potent blockers of the glutamate receptors. Joro spider toxin (JSTX) derived from Nephila clavata has been found to block excitatory postsynaptic potentials and glutamate-evoked responses in the neuromuscular synapse of crustacea, the squid giant synapse and the mammalian brain synapse. Structures of the toxins (JSTXs, NSTXs) of spiders belonging to the genus Nephila were determined and it was found that a unique 2,4-dihydroxyphenylacetyl asparaginyl cadaverine part was conserved between all toxins, indicating that this part is intimately involved in the blocking activity.

Labeling of synthesized JSTX-3 was used for histological investigation of glutamate receptors. Using autoradiography ¹²⁵I-JSTX-3 was found to bind at the lobster neuromuscular synapse. A histochemical study utilizing the interaction of biotinylated JSTX-3 with avidin showed specific binding of the toxin in rat hippocampus and cerebellum. JSTX-3 was used for isolation of glutamate receptors from brain. A crude synaptic membrane fraction from rat hippocampus and cerebellum was solubilized by Triton X-100. SDS-PAGE of the affinity purified JSTX-3 binding proteins showed at least 4 bands around 70 K daltons.