Spider Silk Proteins

Abstract

Dragline silk has been shown to consist of two proteins, Spidroins 1 and 2, which form this unique fiber. The cDNAs for these two proteins have been sequenced and a structure proposed which accounts for both the tensile strength and elasticity of dragline silk. INTRODUCTIONSpiders are unique creatures due to the presence of glands in their abdomen producing silk. They are also unique in the use of silk throughout their life span and the nearly total dependence on silk for their evolutionary success. Although spiders have been studied since earliest man, the first papers using a scientific approach to spider webs and silk appeared in the 1800s. One of the earliest was by John Blackwell describing the construction of webs by spiders [1]. The following decades resulted in studies of the biology of the spiders and their anatomy, but little information was published about the silk itself. In 1907 Benton published one of the earliest studies describing properties of the silk [2]. In that same year Fischer demonstrated the protein nature of the silk by showing the predominant presence of amino acids [3]. There were periods of fairly intense study prior to World War HI and in the late 1950s. However progress, especially when compared to silkworm silk, was relatively meager. Beginning in the 1970s the laboratories of Work, Gosline and Tillinghast revived interest in spider silk with several papers describing physical, mechanical and chemical properties of spider silks. Despite the efforts of these groups and others, the structure of the spider silk protein(s) remained unknown.Spider webs are constructed from several different silks. Each of these silks is produced in a different gland. The glands occur as bilaterally symmetric paired sets. Although each of the glands has its own distinctive shape and size, their functional organization is similar. The majority of the gland serves as a reservoir for soluble silk protein which is synthesized in specialized cells at the distal end of the gland. The soluble silk is pulled down a narrow duct during which the physical and chemical changes occur which produce the solid silk fiber. There is a valve at the exit to the spinneret which can control the flow rate of the fiber and may control the fiber diameter to a small degree. The silk exits through the spinnerets, of which there are three pairs, anterior, median and posterior.Due to their size and ease of study, the major ampullate glands have received the most attention. Thus, most of what is known about the synthesis of silk proteins is based on the study of that gland. However, morphological and histochemical studies of the other glands support the ideas developed for the major ampullate gland. The synthesis of the silk protein(s) takes place in specialized columnar epithelial cells [4] which appear to lack a Golgi apparatus. There appears to be at least two different types of cells producing protein [5] which correlates with our data on the composition of the silk from these glands. The newly synthesized protein appears within ...

Structure and Structural Changes of the Silk Fibroin from Samia cynthia ricini Using Nuclear Magnetic Resonance Spectroscopy

“…Here, three kinds of solid-state NMR methods, namely quantitative use of the 13 C chemical shift, 2D spin-diffusion NMR under off magic angle spinning and REDOR, were applied to determinate the precise structure of the model peptide, Scr34;GGAGGGYGGDG-G(A) 12 GGAGDGYGAG, which is a typical repeated sequence of S. c. ricini silk fibroin. The content of the sequence of the Scr34 peptide can cover about 70% of the whole primary structure of the S. c. ricini silk fibroin.…”

“…13 C CP/MAS NMR Spectroscopy Figure 5 shows the 13 C CP/MAS NMR spectra of the model peptide from S. c. ricini silk fibroin; GGAGGGYGGD-G(A) 12 GGAGDGYGAG after dialysis of a 9 M LiBr solution against water, A, and after TFA treatment, B, together with the film of S. c. ricini silk fibroin prepared from the silk fibroin stored in the silkgland, C. Here ''TFA treatment'' means that the peptide was dissolved in TFA and then precipitated in diethylether. The chemical shifts of the spectrum A, 20.2 ppm for Ala Cb, 48.7 ppm for Ala Ca and 171.9 ppm for Ala carbonyl carbons, clearly show that the conformation is a b-sheet.…”

“…This is similar to the primary structure of dragline (major ampullate) silk from spider although the length of poly-Ala is shorter in the dragline silk: (Ala) [5][6] . [11,12] In our laboratory, several solid-state NMR techniques as well as solution NMR spectroscopy coupled with stable isotope labeling of the silk samples have been applied to clarify the secondary structures of these silk fibroins before and after spinning. [13] For example, the structure of B. mori silk fibroin before spinning in the solid state (Silk I) has been proposed to be a ''repeated b-turn type II structure'' [14,15] by using several solid-state NMR techniques, where the stable isotope labeled model peptide (Ala-Gly) 15 was effectively used for the structural determination.…”

Biomolecular Materials. Report of the January 13-15, 2002 Workshop

“…Nature's materials have exceptional strength and toughness Hinman et al, 1993;Waite et al, 1998;Curry 1977;Jackson1988). Spider dragline silk, synthesized primarily from carbon, hydrogen, oxygen and nitrogen, has long been envied for its fracture energy which is two orders of magnitude greater than that of high tensile steel (Hinman et al, 1993;Heslot 1998).…”

“…Spider dragline silk, synthesized primarily from carbon, hydrogen, oxygen and nitrogen, has long been envied for its fracture energy which is two orders of magnitude greater than that of high tensile steel (Hinman et al, 1993;Heslot 1998). Its use has been hampered by the availability of the material, (which is more difficult to obtain than the weaker material from easily grown silk worms.)…”