Structural components of spider silk are safely stored and assembled on demand with help from a molecular switch.
"Five times the tensile strength of steel and triple that of the currently best synthetic fibers: Spider silk is a fascinating material…How do spiders form long, highly stable and elastic fibers from the spider silk proteins stored in the silk gland within split seconds?…
"Spider silk consists of protein molecules, long chains comprising thousands of amino-acid elements. X-ray structure analyses show 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 may not approach each other too closely; otherwise the proteins would clump up instantaneously. Hence, these molecules must have some kind of special storage configuration…
"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."'Our results have shown that the molecular switch we discovered at the C-terminal end of the protein chain is decisive, both for safe storage and for the fiber formation process,' says Franz Hagn." (Science Daily 2010)
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