Aspects of X-ray diffraction on single spider fibers

Structure of silk by raman spectromicroscopy: From the spinning glands to the fibers

“…Typically, the b-sheet content that is found by this method is 37 6 3% for the dragline, 45 6 3% for the cocoon silk of S. c. ricini and 50 6 3% for that of B. mori, 33 which is basically consistent with crystallinity measurements. 11,[44][45][46][47] Comparison between the b-sheet content determined from the spectroscopic data and the percentage of amino acids that may potentially be included into the b-sheets lead to the conclusion that for the dragline fiber the AG and GGA motifs adjacent to the (A) n are incorporated into the b-sheets, 33 which is consistent with the literature. [48][49][50] Other results have shown that the minor ampullate (Mi) and cylindriform (Cyl) silks belong to the same structural family than the Ma silk as they are composed of highly oriented b-sheets (35-37%) dispersed in an amorphous matrix made of other slightly oriented secondary structures.…”

“…11,12 Nevertheless, some of these techniques require a certain degree of treatment of the fiber that might affect its structure and/or they provide no molecular (i.e., spectroscopic) information. On the other hand, it is possible to study efficiently the structure of silk by Raman spectromicroscopy without any sample preparation.…”

Orientational order of Australian spider silks as determined by solid‐state NMR

“…X-ray diffraction results also suggest that Argiope argentata dragline silk contains a large amount of material with shortrange order or noncrystalline components. 9 Supporting data from positron annihilation spectroscopy, which gives quantitative information about the number and dimensions of free-volume sites, or amorphous regions, 43,44 indicated that the Nephila silk was more crystalline than Argiope silk (A. Hill, personal communication). We have previously shown that diet can vary the amino acid content of Argiope dragline silk 45 and this can show great inter-and intraspecies variation.…”

“…4 Gly and Ala, the most common amino acid residues found in silk, are typically located in repeated blocks in dragline silk and, although dependent on the spinning process, the secondary structure contains a large proportion ofsheet. [5][6][7][8][9] The crystalline domains are thought to consist of Ala-rich, antiparallel -sheets, the structure of which underpin the superior tensile strength of silk. 10,11 From amino acid analysis of cDNA, a repeating unit made up of three segments (consisting of 6, then 13 and 15 amino acids in length) dominated by an Ala-rich sequence of 5-7 residues has been found.…”

The elaborate structure of spider silk

“…After secretion from the silk glands, silk proteins are in aqueous solution and lack considerable secondary or tertiary structure. 37 Particularly in their repetitive core domains, however, the long repetitive sequences permit weak but numerous intra-and intermolecular interactions between neighboring domains and proteins upon passage through the spinning duct. These interactions result in the formation of secondary, tertiary and quaternary structure.…”