Presynaptically acting snake venom phospholipase A2 enzymes attack unique substrates

Area of Science:

• Neuroscience
• Biochemistry
• Toxicology

Background:

• Snake venom phospholipase A2 (PLA2) toxins are implicated in neurotoxicity.
• The mechanism by which presynaptic-active PLA2 toxins (PS+) stimulate acetylcholine (ACh) release remains unclear.
• Investigating the role of fatty acid liberation and bovine serum albumin (BSA) interaction is crucial.

Purpose of the Study:

• To determine if presynaptic action of snake venom PLA2 toxins is due to BSA-resistant fatty acid release or specific fatty acid types.
• To differentiate the mechanisms of PS+ and presynaptic-inactive (PS-) PLA2 enzymes.

Main Methods:

• Incubation of synaptosomes with snake venom PLA2 enzymes and BSA.
• Quantification of fatty acid production, including palmitic acid.
• Assessment of acetylcholine (ACh) release from synaptosomes.

Main Results:

• PS+ PLA2 enzymes (beta-bungarotoxin, scutoxin) stimulated ACh release, while PS- enzymes (from Naja naja atra and Naja naja kaouthia) did not in the presence of BSA.
• BSA did not differentially extract fatty acids from PS- versus PS+ enzymes.
• PS+ enzymes produced significantly more palmitic acid, but free palmitic acid levels in synaptosomes were similar for PS+ and PS- enzymes.
• BSA removed the excess palmitic acid produced by PS+ enzymes from the synaptosomes.

Conclusions:

• The total amount of palmitic acid produced does not solely account for PS+ PLA2-induced ACh release.
• BSA's ability to remove palmitic acid suggests it does not directly mediate the presynaptic effect.
• Higher palmitic acid production by PS+ enzymes may indicate access to distinct phospholipid substrates or altered substrate specificity.
• Potential mechanisms for PS+ PLA2 action include site-directed enzymatic activity and protein acylation.