Abstract

Spider silk is a material that has long been renowned for its remarkable combination of strength and elasticity. Fibers of spider silk are composed exclusively of protein, making them a system amenable to study using techniques that were developed for the study of other, non-fibrous proteins. Currently, the sequences of the proteins that compose many silk fibers are known. However, it is not currently understood how the material properties arise from these surprisingly simple proteins. To this end, two different approaches have been taken to explore the structure-function relationships of silk proteins.

The first approach was to produce a synthetic version of one of the two protein components of spider silk: MaSp1. The two proteins that compose major ampullate silk are difficult to resolubilize intact, chemically inseparable, and can only be obtained in very limited quantities from their natural source. Further characterization of these proteins necessitates their production using a recombinant host. Synthetic genes were designed and constructed for expression in Escherichia coli. For unknown reasons, expression of this family of gene constructs was undetectable for all but a short construct which resulted in a protein of 29kDa. This short protein was unable to form a film or fiber.

The second approach was to apply Molecular Dynamics, a computer modeling system, to study the molecular structure and behavior of MaSp1, MaSp2 and flagelliform silk proteins. Behavior of a peptide modeled on the predicted structure of a sequence that occurs frequently in both MaSp2 and flagelliform silk proteins showed that these regions of the silk proteins are not likely to have any strongly preferred, energetically minimal structures. Instead, these regions of silk are likely to remain highly mobile, regardless of their immediate environment. Larger peptide aggregate studies that include crystalline β-sheet regions formed from poly-alanine segments and the highly mobile glycine rich regions correspond well with experimentally determined structural parameters of silk fibers. Furthermore, these models exhibit mechanical properties that are very similar to natural silk samples.