Snake presynaptic neurotoxins with phospholipase A2 activity are potent inducers of paralysis through inhibition of the neuromuscular junction. These neurotoxins were recently shown to induce exocytosis of synaptic vesicles following the production of lysophospholipids and fatty acids and a sustained influx of Ca2+ from the medium. Here, we show that these toxins are able to penetrate spinal cord motor neurons and cerebellar granule neurons and selectively bind to mitochondria. As a result of this interaction, mitochondria depolarize and undergo a profound shape change from elongated and spaghetti-like to round and swollen. We show that snake presynaptic phospholipase A2 neurotoxins facilitate opening of the mitochondrial permeability transition pore, an inner membrane high-conductance channel. The relative potency of the snake neurotoxins was similar for the permeability transition pore opening and for the phospholipid hydrolysis activities, suggesting a causal relationship, which is also supported by the effect of phospholipid hydrolysis products, lysophospholipids and fatty acids, on mitochondrial pore opening. These findings contribute to define the cellular events that lead to intoxication of nerve terminals by these snake neurotoxins and suggest that mitochondrial impairment is an important determinant of their toxicity.

Results gathered to date, encompassing 18 out of the approximately 85 species of Micrurus, reveal a dichotomy of venom phenotypes regarding the relative abundance of the omnipresent phospholipases A2 (PLA2) and 'three-finger' toxins (3FTx): a group of species express a PLA2-predominant venom composition, while others display a 3FTx-predominant compositional pattern. These two divergent toxin expression phenotypes appear to be related to phylogenetic positions and geographical distributions along a North-South axis in the Americas

Concerning elapid venoms, the low immunogenicity of 3FTXs makes generating homogeneous antivenoms difficult [2]. The elapid 3FTXs are peptides with associated non-enzymatic activity, ranging from 60 to 85 amino acids. They contain eight highly conserved cysteine residues that form 4 disulfide bridges that stabilize their hydrophobic core, from which emerge three loops that bear 3–5 antiparallel beta-strands. Besides, some 3FTXs also contain an extra pair of cysteine residues that forms one more disulfide bridge located at one of the loops. 3FTXs encompass many proteins with diverse functions like cytotoxicity (e.g. cardiotoxins) [3], [4] and neurotoxicity (e.g. α-neurotoxins, fasciculins, muscarinic toxins, L-type calcium channel blockers) [5], [6], [7]. Snake venom composition from elapids and from their related colubrids show that PLA2 and 3FTXs are not only the most abundant protein families [8], [9], but also, the most toxic ones [10].

Particularly, proteins found in venoms, which can be nested in super-protein families, such as phopholipases A2 (PLA2), snake venom metalloproteinases (SVMP), serine proteinases and three-finger toxins (3FTXs), for instance, are the main toxins responsible for snake envenomation.