Morphological and compositional basis of silk fiber function in Actias luna

Silk is a highly versatile natural protein fiber with a wide range of uses, yet its diversity in composition and function remains poorly understood across the tree-of-life. This study investigates the silk of the Luna moth, Actias luna (Saturniidae), known to produce high-density cocoons with distinct fiber characteristics. Despite the broad recognition of A. luna as an important species for research and education, its silk production, silk fiber composition, and properties remain under characterized, particularly in comparison to other Saturniidae and model species such as Bombyx mori. Building from the recently assembled A. luna genome, this study examines key repeat motifs and amino acid composition of the silk fibroin heavy chain (FibH) protein in relation to silk fiber properties across species. We assessed the physical properties of native and degummed A. luna silk fibers, evaluating the effects of degumming time and treatment on fiber morphology and mechanical properties. Actias luna silk fibers have similar properties to other saturniid silks, aligning with established trends that link fiber characteristics to structural protein composition. Silk gland architecture and regional composition shifts in A. luna were analyzed, highlighting differences that correlate to differential protein expression. Analyses of fiber characteristics were further expanded to silk fibers produced by A. luna at different developmental stages. Variation in larval characteristics, fiber morphology, and silk fiber composition across larval instars suggests that life stage-specific silk fiber function may stem from differences in protein expression and silk fiber use. These findings advance understanding of how evolutionary and developmental shifts influence silk fiber properties, providing a foundation for rational design of protein-based biomaterials with tunable mechanical and structural characteristics for biomedical applications.