Beneath the surface: A new northern species of Trogloraptor (Araneae: Trogloraptoridae), genetic diversity and natural history

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  Beneath the surface: A new northern species of Trogloraptor (Araneae: Trogloraptoridae), genetic diversity and natural history Abstract We present a morphological description of a recently discovered species of spider in the family Trogloraptoridae from the Columbia River Gorge in northwestern Oregon. The family was previously monotypic (Trogloraptor marchingtoni) and only known from populations near the southwestern Oregon—northern California border. Trogloraptor tulishpun sp. nov. retains the key family synapomorphy, distinctive subsegmented raptorial tarsi, and an oblique membranous division of the basal segment of the anterior lateral spinnerets. Trogloraptor tulishpun is distinguished from T. marchingtoni by its color pattern, clypeal height, vulvar and palp structure. We have found T. tulishpun in four localities in the Columbia River Gorge, which show little mitochondrial sequence divergence from one another, but are highly genetically distinct from T. marchingtoni. Troglo...

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