Climatic and density-dependent drivers of population dynamics in a hazardous urban scorpion species over seven years

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  Climatic and density-dependent drivers of population dynamics in a hazardous urban scorpion species over seven years Abstract This link goes to a Portuguese section Tityus serrulatus Lutz & Mello (Scorpiones: Buthidae) is the most medically important scorpion in Brazil, responsible for a growing number of accidents in urban areas. Despite its relevance, the population dynamics of this species in anthropogenic habitats remain poorly understood, particularly regarding the influence of abiotic factors on its abundance and reproduction. We analysed long-term data (2006–2013) from T. serrulatus collected in an urban cemetery in the municipality of Americana, São Paulo State, Brazil. Using spatiotemporal mixed models, we evaluated the effects of temperature and humidity at the graves on the abundance of brooded and non-brooded individuals, as well as on the ratio between the two reproductive groups. A total of 21,489 individuals were recorded, including 463 brooded individuals. W...

Arg–Tyr cation–π interactions drive phase separation and β-sheet assembly in native spider dragline silk

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Arg–Tyr cation–π interactions drive phase separation and β-sheet assembly in native spider dragline silk

Abstract

Liquid–liquid phase separation (LLPS) is a fundamental principle of protein organization in intrinsically disordered proteins (IDPs) and biomaterials, yet the residue-level interactions that link condensation to structural ordering remain poorly defined. In spider dragline silk, LLPS is believed to initiate the transition from soluble spidroin dope into β-sheet–rich fibers that provide exceptional toughness, yet how sequence-specific motifs govern this process has been unclear. Here, we combine isotope-edited solution NMR, dynamic nuclear polarization (DNP)–enhanced solid-state NMR, molecular dynamics simulations, and AlphaFold3 modeling to define the molecular role of arginine and tyrosine in Latrodectus hesperus dragline silk. Phosphate triggers LLPS while preserving intrinsic disorder, with arginine exhibiting the largest chemical shift perturbations. Simulations reveal that phosphate displaces hydration water to promote Arg–Tyr cation–π interactions and weaken Arg–poly(Ala) contacts. Solid-state NMR directly detects Arg–Tyr contacts in spun fibers, demonstrating that arginine is partially incorporated into β-sheet interfaces while tyrosine frequently adopts β-turn conformations. AlphaFold3 models corroborate these interfacial geometries and reproduce experimental chemical shifts, supporting persistent Arg–Tyr interactions at structured–unstructured boundaries. Together, these results identify Arg–Tyr contacts as critical “sticker” interactions that mediate condensation, nucleate local order, and stabilize fiber architecture. More broadly, this work establishes a mechanistic link between residue-specific chemistry, LLPS, and hierarchical assembly in a structural protein. These insights highlight how weak multivalent interactions bridge disordered and ordered states, providing a general framework for condensate-driven assembly in biology and guiding biomimetic material design.

Johnson, H. R., Chalek, K., Elathram, N., Chau, A. T., Domingo, A. R., Aldana, J. E., Nguyen, H., De Loera, A., Duarte, B. A., Shapakidze, L., Onofrei, D., Debelouchina, G. T., Lorenz, C. D., & Holland, G. P. (2025). Arg–Tyr cation–π interactions drive phase separation and β-sheet assembly in native spider dragline silk. Proceedings of the National Academy of Sciences, 122(52), e2523198122. https://doi.org/10.1073/pnas.2523198122