Hidden diversity in plain sight: four new species of Nemesia (Araneae: Mygalomorphae) from the Córdoba Province of Spain

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  Hidden diversity in plain sight: four new species of Nemesia (Araneae: Mygalomorphae) from the Córdoba Province of Spain Abstract A taxonomic revision of the species of Nemesia Audouin, 1826, distributed in the vicinity of Córdoba City, southern Spain, is presented. Four new species are described: Nemesia morana sp. nov. (female), N. kodama sp. nov. (male and female), N. rosae sp. nov. (male and female), and N. tamajoni sp. nov. (male and female). These species are distinguished by distinct morphological characters, including the shape of the spermathecae, palpal bulbs, and spinnerets, as well as by burrow architecture. Fieldwork was conducted across two of the three major habitat types in the region—the humid, forested mountains of Sierra Morena and the croplands and riparian forests of the Guadalquivir Valley—while the third, the “campiña”, which is mainly composed of agricultural landscapes, remains poorly explored. Sampling methods included pitfall trapping and the direct e...

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