Establishing the relationship between structure and mechanical function in silks

Dragline silk protein fibers from the spider Nephila clavipes have mechanical properties that make them superior to high tenacity nylon, which is also a polyamide, and far superior to other protein fibers, including silkworm silk. In examining the relationship between the mechanical properties of the fibers and their molecular structure, one should look at the secondary structural elements, including beta-sheets and bends, that have been derived by solid state NMR experiments and at the crystallinity and long-range structures obtained by X-ray measurements. A major conclusion from the present data is that nature has engineered in a certain amount of randomness, and that the protein is inadequately described as being simply a repeat of a consensus sequence. This suggests that approaches to designing synthetic silk-like proteins will need to include this randomness, rather than being based on high polymers of simple repeats of the consensus sequence.