Frontoxins, three-finger toxins from Micrurus frontalis venom, decrease miniature endplate potential amplitude at frog neuromuscular junction

Abstract

Neurotoxicity is a major symptom of envenomation caused by Brazilian coral snake Micrurus frontalis. Due to the small amount of material that can be collected, no neurotoxin has been fully sequenced from this venom. In this work we report six new three-finger like toxins isolated from the venom of the coral snake M. frontalis which we named Frontoxin (FTx) I-VI. Toxins were purified using multiple steps of RP-HPLC. Molecular masses were determined by MALDI-TOF and ESI ion-trap mass spectrometry. The complete amino acid sequence of FTx II, III, IV and V were determined by sequencing of overlapping proteolytic fragments by Edman degradation and by de novo sequencing. The amino acid sequences of FTx I, II, III and VI predict 4 conserved disulphide bonds and structural similarity to previously reported short-chain alpha-neurotoxins. FTx IV and V each contained 10 conserved cysteines and share high similarity with long-chain alpha-neurotoxins. At the frog neuromuscular junction FTx II, III and IV reduced miniature endplate potential amplitudes in a time-and concentration-dependent manner suggesting Frontoxins block nicotinic acetylcholine receptors.

Characterization of a new muscarinic toxin from the venom of the Brazilian coral snake Micrurus lemniscatus in rat hippocampus

“…Despite MT-Mlα presents similarity to FTx-III, that act on nicotinic acetylcholine receptors (Moreira et al, 2010), we demonstrated in the present work that the MT-Mlα was able to interact on mAChRs. Furthermore, it is important to point out that the ability of the Frontoxins to displace the binding of a muscarinic ligand was not investigated for the authors.…”

“…Concerning the venoms of Brazilian snakes of the genus Micrurus (belong to Elapidae family), they are particularly rich in pre-and pos-synaptic neurotoxins that have the cholinergic system as their target of action (Dal Belo et al, 2005;Moreira et al, 2010;Silva et al, 1991;Vital-Brazil, 1987;Vital-Brazil andFontana (1983/1984) However, few investigations have dealt with isolated toxins from venoms of these snakes. Some neurotoxins endowed of PLA2 activity (Oliveira et al, 2008) or neurotoxins that have high affinity to nAChRs (Olamendi-Portugal et al, 2008) have been isolated and characterized from genus Micrurus.…”

Biological characterization of the Amazon coral Micrurus spixii snake venom: Isolation of a new neurotoxic phospholipase A2

“…The range of actions and chemical compositions of venoms from the genus Micrurus is an adaptation to different habitats, which is an useful evolutionary tool for this species (Tanaka et al, 2010). This variation in proteins and actions of the venom would enable snakes to have a predatorprey type selectivity making their diet specialized (Bernarde, 2011;Moreira et al, 2010). Q2,3 In Micrurus venom there is a considerable quantity of different toxins such as C-type lectins, natriuretic peptides precursors (NPP), L-amino acid oxidase (LAAO), metalloproteinases, Kunitz-type inhibitors, serine proteases, lysosomal acid lipase, hyaluronidase and alkaline phosphomonesterases (Corrêa-Netto et al, 2011;Leão et al, 2009).…”

Novelty in three-finger toxin evolution

“…It must be noted that two of the Micrurus toxins with published α-neurotoxic activity belong to Clade B and only display 19% conservation of these sites [216,217]. This could be due to Clade B's close relationship to the Type III α-neurotoxins, a preservation of the putative ancestral activity despite these amino acid changes, or convergent evolution in function.…”

“…Those eight-cysteine Micrurus sequences that have been previously characterized are marked in neuromuscular response [215,216,218]. The distribution of α-neurotoxicity suggests that phylogenetic position alone is not enough to assign putative function to Micrurus 3FTx sequences.…”