Postsynaptic short-chain neurotoxins from Pseudonaja textilis. cDNA cloning, expression and protein characterization.

Two lethal proteins, which specifically bind to the nAChR from Torpedo californica, were isolated from the venom of Pseudonaja textilis, the common brown snake from Australia. The isolated proteins have masses of 6236 and 6345 Da and are structurally related to short-chain neurotoxins from other elapids. Six cDNAs encoding isoforms of related neurotoxins were cloned using the RT-PCR of the venom gland mRNAs. The sequences of the corresponding proteins consist of 57-58 amino acid residues and display several unique features when compared with all known short-chain neurotoxins. Accordingly, they grouped separately in phylogenetic analysis. The six cDNAs were expressed in Escherichia coli and the recombinant proteins were characterized. They have similar masses and display similar toxicities and binding constants to the nAChR as the native toxins isolated from the venom. Thus, a new group of short-chain postsynaptic neurotoxins from the venom of an Australian elapid has been characterized.