Origin, structure, and composition of the spider major ampullate silk fiber revealed by genomics, proteomics, and single-cell and spatial transcriptomics.

Spiders produce nature's toughest fiber using renewable components at ambient temperatures and with water as solvent, making it highly interesting to replicate for the materials industry. Despite this, much remains to be understood about the bioprocessing and composition of spider silk fibers. Here, we identify 18 proteins that make up the spiders' strongest silk type, the major ampullate fiber. Single-cell RNA sequencing and spatial transcriptomics revealed that the secretory epithelium of the gland harbors six cell types. These cell types are confined to three distinct glandular zones that produce specific combinations of silk proteins. Image analysis of histological sections showed that the secretions from the three zones do not mix, and proteomics analysis revealed that these secretions form layers in the final fiber. Using a multi-omics approach, we provide substantial advancements in the understanding of the structure and function of the major ampullate silk gland as well as of the architecture and composition of the fiber it produces.

Regionalization of cell types in silk glands of Larinioides sclopetarius suggest that spider silk fibers are complex layered structures.

In order to produce artificial silk fibers with properties that match the native spider silk we likely need to closely mimic the spinning process as well as fiber architecture and composition. To increase our understanding of the structure and function of the different silk glands of the orb weaver Larinioides sclopetarius, we used resin sections for detailed morphology, paraffin embedded sections for a variety of different histological stainings, and a histochemical method for localization of carbonic anhydrase activity. Our results show that all silk glands, except the tubuliform glands, are composed of two or more columnar epithelial cell types, some of which have not been described previously. We observed distinct regionalization of the cell types indicating sequential addition of secretory products during silk formation. This means that the major ampullate, minor ampullate, aciniform type II, and piriform silk fibers most likely are layered and that each layer has a specific composition. Furthermore, a substance that stains positive for polysaccharides may be added to the silk in all glands except in the type I aciniform glands. Active carbonic anhydrase was found in all silk glands and/or ducts except in the type I aciniform and tubuliform glands, with the strongest staining in aggregate glands and their ductal nodules. Carbonic anhydrase plays an important role in the generation of a pH gradient in the major ampullate glands, and our results suggest that some other glands may also harbor pH gradients.

Hemin is able to disaggregate lysozyme amyloid fibrils into monomers.

Lysozyme amyloidosis (ALys) is a disease of the gastrointestinal tract, liver and kidneys, which is caused by the accumulation of insoluble fibrils of lysozyme in the tissues of above organs. The ALys can be cured by disintegration and clearance of the fibrils from the affected tissues and organs. It is thought that protein fibrils are extremely stable. Consequently, small molecule-induced dissociation of fibrils under physiological conditions is really challenging. Here, we report kinetic and thermodynamic analyses of hemin-induced dissociation of hen egg white lysozyme amyloid fibrils. We examined the effect of hemin on the kinetics of dissociation of lysozyme fibrils. We observed that the hemin binding dissociates fibrils in a concentration dependent manner within a reasonable time. Studies of structural, morphological properties and gel filtration chromatography indicate that fibrils dissociate mainly into monomeric species. The conformational, hydrodynamic, unfolding and stability studies of the resolubilized proteins show that dissociated monomers possess characteristics of partially folded intermediate state of the protein. We also find that hemin-induced fibril dissociation mainly depends on the kinetic and thermodynamic stability of the fibrils. These results suggest that non-toxic derivatives of hemin and other porphyrins could pave a way for therapeutic intervention in amyloidosis and related pathologies.