Amyloidogenic nature of spider silk

Abstract

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.