Differential Hematotoxic Activity of Southeast Asian Pit Viper Venoms: The Cross-Neutralizing Effect of Available Antivenoms

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  Image Credit: Creative Commons (some rights reserved) CC BY-NC Photo 111998430, (c) Nicholas Hess Differential Hematotoxic Activity of Southeast Asian Pit Viper Venoms: The Cross-Neutralizing Effect of Available Antivenoms Abstract Background/Objectives : Pit vipers (subfamily Crotalinae) are responsible for a large proportion of snakebite envenoming cases in Southeast Asia. Envenomation by these snakes commonly causes hematotoxic effects, including platelet dysfunction and coagulation disturbances. Although antivenom remains the mainstay of treatment, species-specific antivenoms are not available for several regional pit viper species. This study evaluated the hematotoxic activities of selected Southeast Asian pit viper venoms and the cross-neutralizing capacity of commercially available antivenoms.  Methods : Venoms from five medically important pit viper species— Calloselasma rhodostoma ,  Trimeresurus albolabris ,  T. hageni ,  T. purpureomaculatus , ...

Spider venom phospholipase D toxin structure: Interfacial binding site, mechanism, activation, and head group preference

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Spider venom phospholipase D toxin structure: Interfacial binding site, mechanism, activation, and head group preference

Abstract

Envenomation by sicariid spiders such as the brown recluse can cause loxoscelism, a syndrome involving localized dermonecrosis and/or systemic effects like hemolysis. The causative venom toxins are unusual interfacial phospholipase D enzymes that cyclize sphingolipid and lysophospholipid substrates when bound to membrane surfaces. Crystal structures of several of these toxins have been reported, but none of them directly illuminates how lipids bind in the active site and at the interfacial binding site (IBS); indeed, as a general rule the lipid interfaces of peripheral membrane proteins resist crystallographic determination. Here, however, we report X-ray crystal structures at 1.85 to 2.6 Å resolution of a venom toxin from the Chilean six-eyed sand spider Sicarius levii (terrosus) bound to a micelle-like agglomeration of product and substrate sphingolipids. Each enzyme subunit binds three sphingolipid molecules, one in the active site and two at adjacent noncatalytic sites, generating an interface that approximates the IBS predicted by molecular dynamics. The conformations of substrate and cyclic product in the active site definitively confirm our previously proposed catalytic mechanism. Comparisons with lipid-free structures show conformational changes in two loops that suggest a mechanism for allosteric/surface activation. Docking studies suggest that the variable preference of these toxins for phosphocholine and phosphoethanolamine head groups involves subtle changes in size and shape of the active-site pocket. The structures reveal key facets of the molecular basis of loxoscelism and show that in favorable cases crystallography can illuminate the IBS of peripheral membrane proteins.

Sundman, A. K., Binford, G. J., Montfort, W. R., & Cordes, M. H. (2026). Spider venom phospholipase D toxin structure: Interfacial binding site, mechanism, activation, and head group preference. Proceedings of the National Academy of Sciences, 123(15), e2513997123. https://doi.org/10.1073/pnas.2513997123