Background: Phospholipase D toxins from brown spider venoms can cause disease in humans. Results: Different toxin family members show specificity for lipid substrates with choline or ethanolamine headgroups or can be ambiguous. Conclusion: Spider phospholipase D toxins have evolved diverse substrate preferences. Significance: The diverse substrate preference may be significant for predation and the mammalian toxicity of venom.

Venoms of brown spiders in the genus Loxosceles contain phospholipase D enzyme toxins that can cause severe dermonecrosis and even death in humans. These toxins cleave the substrates sphingomyelin and lysophosphatidylcholine in mammalian tissues, releasing the choline head group. The other products of substrate cleavage have previously been reported to be monoester phospholipids, which would result from substrate hydrolysis. Using 31P NMR and mass spectrometry we demonstrate that recombinant toxins, as well as whole venoms from diverse Loxosceles species, exclusively catalyze transphosphatidylation rather than hydrolysis, forming cyclic phosphate products from both major substrates. Cyclic phosphates have vastly different biological properties from their monoester counterparts, and they may be relevant to the pathology of brown spider envenomation.

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