A new silk: Mechanical, compositional, and morphological characterization of leafhopper (Kahaono montana) silk

Azadirachtin inhibits the development and metabolism of the silk glands of Spodoptera frugiperda and affects spinning behavior

BACKGROUND

Spodoptera frugiperda is a major agricultural pest, and the dispersal of its larvae by spinning silk is one of the causes of crop damage. At present, there are relatively few reports of pest control that affect larvae spinning silk. In this study, the effect of spinning behavior of the S. frugiperda larvae was investigated through a series of experiments.

RESULTS

The 3rd instar larvae of S. frugiperda were exposed to azadirachtin, and the pathological changes in the silk glands of S. frugiperda and the differences in their metabolites were analyzed by scanning electron microscopy, histological sectioning, transmission electron microscopy and metabolomics. The results showed that azadirachtin could affect the silk gland of S. frugiperda. After 48 h of treatment with azadirachtin, the silk gland lumen of S. frugiperda appeared vacuolated. KEGG showed that 31 different metabolites were identified, of which 12 were upregulated and 19 were downregulated. These metabolites were enriched in 15 different metabolic pathways, which indicated that the silk gland of S. frugiperda was closely related to the formation of fatty acids and energy metabolism for the silk formation process.

CONCLUSIONS

This study provides a preliminary report of the effect of azadirachtin on the spinning behavior of the S. frugiperda larvae. Metabolomic results indicated that histidine, glycine and leucine, which are related to serine protein synthesis, were down-regulated. Azadirachtin can damage the silk glands of S. frugiperda and thus affect spinning behavior. This provides the basis for the control of S. frugiperda by spinning silk. © 2022 Society of Chemical Industry.

Biomimetic repeat protein derived from Xenopus tropicalis for fibrous scaffold fabrication

Collagen, silk, and elastin are the fibrous proteins consist of representative amino acid repeats. Because these proteins exhibited distinguishing mechanical properties, they have been utilized in diverse applications, such as fiber-based sensors, filtration membranes, supporting materials, and tissue engineering scaffolds. Despite their infinite prevalence and potential, most studies have only focused on a few repeat proteins. In this work, the hypothetical protein with a repeat motif derived from the frog Xenopus tropicalis was obtained and characterized for its potential as a novel protein-based material. The codon-optimized recombinant frog repeat protein, referred to as 'xetro', was produced at a high rate in a bacterial system, and an acid extraction-based purified xetro protein was successfully fabricated into microfibers and nanofibers using wet spinning and electrospinning, respectively. Specifically, the wet-spun xetro microfibers demonstrated about 2- and 1.5-fold higher tensile strength compared with synthetic polymer polylactic acid and cross-linked collagen, respectively. In addition, the wet-spun xetro microfibers showed about sevenfold greater stiffness than collagen. Therefore, the mass production potential and greater mechanical properties of the xetro fiber may result in these fibers becoming a new promising fiber-based material for biomedical engineering.

Comparison of fibroin cDNAs from webspinning insects: insight into silk formation and function

Embiopterans (webspinning insects) are renowned for their prolific use of silk. These organisms spin silk to construct elaborate networks of tubes in which they live, forage, and reproduce. The silken galleries are essential for protecting these soft-bodied insects from predators and other environmental hazards. Despite the ecological importance of embiopteran silk, very little is known about its constituent proteins. Here, we characterize the silk protein cDNAs from four embiopteran species to better understand the function and evolution of these adaptive molecules. We show that webspinner fibroins (silk proteins) are highly repetitive in sequence and possess several conserved characteristics, despite differences in habitat preferences across species. The most striking similarities are in the codon usage biases of the fibroin genes, particularly in the repetitive regions, as well as sequence conservation of the carboxyl-terminal regions of the fibroins. Based on analyses of the silk genes, we propose hypotheses regarding codon bias and its effect on the translation and replication of these unusual genes. Furthermore, we discuss the significance of specific fibroin motifs to the mechanical and structural characteristics of silk fibers. Lastly, we report that the conservation of webspinner fibroin carboxyl-terminal regions suggests that fiber formation may occur through a mechanism analogous to that found in Lepidoptera. From these results, insight is gained into the tempo and mode of evolution that has shaped embiopteran fibroins.

Comparison of embiopteran silks reveals tensile and structural similarities across Taxa

Embioptera is a little studied order of widely distributed, but rarely seen, insects. Members of this group, also called embiids or webspinners, all heavily rely on silken tunnels in which they live and reproduce. However, embiids vary in their substrate preferences and these differences may result in divergent silk mechanical properties. Here, we present diameter measurements, tensile tests, and protein secondary structural analyses of silks spun by several embiid species. Despite their diverse habitats and phylogenetic relationships, these species have remarkably similar silk diameters and ultimate stress values. Yet, ultimate strain, Young's modulus, and toughness vary considerably. To better understand these tensile properties, Fourier transformed infrared spectroscopy was used to quantify secondary structural components. Compared to other arthropod silks, embiid silks are shown to have consistent secondary structures, suggesting that commonality of amino acid sequence motifs and small differences in structural composition can lead to significant changes in tensile properties.

Characterization of silk spun by the embiopteran, Antipaluria urichi

Silks are renowned for being lightweight materials with impressive mechanical properties. Though moth and spider silks have received the most study, silk production has evolved in many other arthropods. One insect group that has been little investigated is Embioptera (webspinners). Embiopterans produce silk from unique tarsal spinning structures during all life stages. We characterize the molecular and mechanical properties of Antipaluria urichi (Embioptera) silk through multiple approaches. First, we quantify the number of silk secretory structures on their forelimbs and the tensile properties of Antipaluria silk. Second, we present silk protein (fibroin) transcripts from an embiopteran forelimb protarsomere cDNA library. We describe a fibroin that shares several features with other arthropod silks, including a subrepetitive core region, a non-repetitive carboxyl-terminal sequence, and a composition rich in glycine, alanine, and serine. Despite these shared attributes, embiopteran silk has several different tensile properties compared to previously measured silks. For example, the tensile strength of Antipaluria silk is much lower than that of Bombyx mori silk. We discuss the observed mechanical properties in relation to the fibroin sequence, spinning system, and embiopteran silk use.

Structure - Property and Structure - Function Relations of Leafhopper (Kahaono montana) Silk

Kahaono montana Evans (Insecta: Hemiptera: Cicadellidae), an endemic Australian leafhopper, is unique among the insect order Hemiptera in producing a silk. In this study, the secondary structure of the protein comprising leafhopper silk, and the surface stretching mechanical properties of this biopolymer, were investigated using Fourier-transform infrared microscopy and atomic force microscopy, respectively. The curve-fitted amide I and amide III bands revealed a composition of 13.1% α-helix, 23.8% β-sheet, 25.5% random coil, and 37.6% aggregated side chains. The molecular stretching behaviour of raw and cleaned silk fibres differed markedly. Analysis of the AFM force curves showed an adhesive property of the raw silk, while the pure fibre showed only the presence of protein. These findings suggest that the silk fibres act as a structural support for other leafhopper secretions and together form a hydrophobic barrier that may protect the insects from rain and natural enemies. This is the first time such a use of silk has been found in a biological system.