Synthesizing spider silk

Abstract

Spider silks have remarkable mechanical properties that make them attractive for medical, military and industrial applications. All spiders can make seven kinds of silk, one type to wrap its prey, one to wrap its eggs and five to construct the web. Each type is biologically engineered to perform its task to perfection. ‘Capture’ silk, which is used to snare insects, is very sticky and can stretch three times its length before breaking. ‘Dragline’ silk, used to anchor the web and form its spokes, has a higher tensile strength than high-tensile steel of the same weight. The protein core of dragline silk fibers is secreted as a mixture of two soluble proteins from epithelial cells in specialized glands. The spinneret, a sophisticated apparatus, transforms the water-soluble silk proteins into the insoluble, strong threads that make up webs. The different silk proteins contain repetitive amino acid sequences that vary slightly, depending on their use. These small changes in sequence can confer different mechanical properties.