Prey-wrapping spider silk as a model for tough and adaptable protein materials

Abstract Spider silks are a diverse family of protein-based fibers with exceptional strength, extensibility, and toughness. While dragline (major ampullate) silk has been studied most extensively, aciniform (AC) silk—used for prey wrapping, egg case lining, and web decoration—exhibits the highest toughness of all spider silks yet remains comparatively underexplored. This review summarizes current knowledge of AC silk across multiple length scales, from the molecular organization of AcSp1 spidroins in the gland, to conformational transitions during fiber formation, to the macroscopic mechanics of natural fibers. Insights from spectroscopy (Raman, solution- and solid-state NMR), microscopy, and computational modeling reveal a hybrid “beads-on-a-string” architecture, with α-helical “beads” connected by flexible “string” domains that partially convert to β-sheets during fibrillization. Advances in recombinant expression and spinning methods have clarified the roles of repetitive and terminal domains while enabling biomimetic fiber production. Emerging directions include the discovery of AcSp2, hydration-induced crosslinking unique to AC silk, and chimeric designs that integrate motifs from multiple silk types. Together, these findings establish AC silk as a model for adaptable, high-performance protein-based materials with broad potential in biomedical and engineering applications.