Broad-Scale Climatic Gradients Drive Multiple Facets of Scorpion Beta Diversity in Northeastern Brazil

Posted by
  Broad-Scale Climatic Gradients Drive Multiple Facets of Scorpion Beta Diversity in Northeastern Brazil ABSTRACT Aim Beta diversity analyses clarify mechanisms structuring ecological communities, but their multidimensional facets remain poorly explored in arthropods. Here, we quantified taxonomic, phylogenetic, and functional beta diversity in scorpions, partitioned these facets into species replacement and richness differences, and evaluated the relative importance of spatial structure and environmental conditions in driving community assembly. Location Northeastern Brazil, South America. Taxon Scorpions (Arachnida: Scorpiones). Methods Taxonomic beta diversity was estimated using species presence across 70 sites in northeastern Brazil. Phylogenetic turnover was calculated from a multi-locus molecular tree, and functional beta diversity was derived from morphometric and ecological traits. All beta diversity facets were decomposed into replacement and richness-difference component...

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

Posted by

 


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