Amyloidogenic nature of spider silk

In spiders soluble proteins are converted to form insoluble silk fibres, stronger than steel. The final fibre product has long been the subject of study; however, little is known about the conversion process in the silk-producing gland of the spider. Here we describe a study of the conversion of the soluble form of the major spider-silk protein, spidroin, directly extracted from the silk gland, to a beta-sheet enriched state using circular dichroism (CD) spectroscopy. Combined with electron microscopy (EM) data showing fibril formation in the beta-sheet rich region of the gland and amino-acid sequence analyses linking spidroin and amyloids, these results lead us to suggest that the refolding conversion is amyloid like. We also propose that spider silk could be a valuable model system for testing hypotheses concerning beta-sheet formation in other fibrilogenic systems, including amyloids.