2026-08-04 アリゾナ大学
A brown recluse spider from Texas, sporting the signature “upside-down violin” mark on its back, which in and by itself does not positively identify a brown recluse. Public domain via Alex Wild and the “Insects Unlocked” Project (University of Texas at Austin)
＜関連情報＞
- https://news.arizona.edu/news/5-things-you-might-not-know-about-brown-recluse
- https://www.pnas.org/doi/10.1073/pnas.2513997123
クモ毒ホスホリパーゼD毒素の構造：界面結合部位、メカニズム、活性化、および頭部基の選択性 Spider venom phospholipase D toxin structure: Interfacial binding site, mechanism, activation, and head group preference
Alexandra K. Sundman, Greta J. Binford, William R. Montfort, and Matthew H. J. Cordes
Proceedings of the National Academy of Sciences Published:April 6, 2026
DOI:https://doi.org/10.1073/pnas.2513997123
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.
