But no one has thus far succeeded in producing the super fibers synthetically. How do spiders form long, highly stable and elastic fibers from the spider silk proteins stored in the silk gland within split seconds? Scientists from the Technische Universitaet Muenchen (TUM) and the University of Bayreuth have now succeeded in unraveling the secret. [Hagn et al., Nature (2010), 465, 242].
Spider silk consists of protein molecules, long chains comprising thousands of amino-acid elements. X-ray structure analyses shows that the finished fiber has areas in which several protein chains are interlinked via stable physical connections. These connections provide the high stability. Between these connections are unlinked areas that give the fibers their great elasticity.
The situation within the silk gland is, however, very different: The silk proteins are stored in high concentrations in an aqueous environment, awaiting deployment. The areas responsible for interlinking are not in close proximity otherwise the proteins would clump instantantly. Hence, these molecules must have some kind of special storage configuration.
Analysis enabled the scientists to unravel the structure and operation of the control element responsible for the formation of the solid fiber
“Under storage conditions in the silk gland these control domains are connected pair-wise in such a way that the interlinking areas of both chains do not lie parallel to each other,” Thomas Scheibel explains. “Interlinking is thus effectively prevented.” The protein chains are stored with the polar areas on the outside and the hydrophobic parts of the chain on the inside, ensuring good solubility in the aqueous environment.
When the protected proteins enter the spinning duct, they encounter an environment with an entirely different salt concentration and composition. This renders two salt bridges of the control domain unstable, and the chain can unfold. Furthermore, the flow in the narrow spinning duct results in strong shear forces. The long protein chains are aligned in parallel, thus placing the areas responsible for interlinking side by side. The stable spider silk fiber is formed.
Work continues to develop various routes.