NMR Characterization of Silk Proteins
Tetsuo AsakuraMakoto DemuraAtsuo UyamaKatsuaki OgawaKeiichi KomatsuLinda K. NicholsonTimothy A. Cross
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Abstract:
Structures of Bombyx mori silk fibroin have been studied in solution, in silkworm and in the solid state by means of solution and solid 13C and 15N NMR spectroscopies. The silk fibroin yields very sharp 13C NMR signals in aqueous solution and in silkworm, indicating the fast segmental motion of the main chain in spite of a fairly high molecular weight, 3 x 105. This makes detailed sequential and conformational analyses of the silk fibroin possible. The structure of the silk fiber in the solid state was studied with 15N CP NMR and 15N isotope-labeled silk fibroins on the basis of the chemical shift tensors in detail. The torsion angles of the glycine, alanine and tyrosine residues were determined.Keywords:
Fibroin
Fiber diffraction
Bombycidae
Alanine
Investigations have been made on the molecular conformation in the solid state of Bombyx mori silk fibroin and the model polypeptides by an infrared spectroscopy (IR).An IR absorbed band assigned to silk I type conformation was only found for the precipitates not having any random coil obtained by an enzyme treatment to the middle silk gland diluted with water and by dissolving silk fibers in an aqueous LiBr solution. On the other hand, the IR absorbed band assigned to α-helical conformation was found together with those of random coil and the silk II type conformation for as-polymerized model polypeptides and silk fibroin threads hydrolyzed by aqueous HCI solution.It is, therefore, concluded that a small amount of α-helix exists in the amorphous part of Bombyx mori silk fibroin.
Fibroin
Random coil
Bombycidae
Helix (gastropod)
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Sericulture generates different natural products with potential medical applications. Silk peptides, worms, or even pupae are commonly employed in traditional Asian medicine with a wide variety of purposes, and some scientific work has been focused on their antidiabetic properties. This work evaluates the postprandial antihyperglycemic activity of fibroin, sericin, and powder made from either larvae or pupae of silkworms, and Bombyx mori L. (Lepidoptera: Bombycidae), employing the silkworm itself as an animal model. The results indicate a reduction in the glucose levels in hemolymph after sucrose or glucose-induced hyperglycemia when these products are included in the diet of the worms.
Bombycidae
Sericulture
Hemolymph
Sericin
Fibroin
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The mRNA that codes for silk fibroin in the silkworm Bombyx mori can be isolated in greater than 90% purity as judged by partial sequence analysis (Suzuki and Brown, 1972). Molecular hybridization experiments using highly purified fibroin mRNA have established that there are one to three genes per haploid complement of DNA in all tissues investigated, including the posterior silk gland where fibroin is synthesized (Suzuki et al., 1972).
Fibroin
Bombyx
Sericin
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The crystalline structure of a kind of nature yellow Silk, derived from the parents of hybrid between Bombyx mori and a yellow cocoon silkworm(natural resources of color cocoon) , and a wildly silkworm silk fibroin were studied by Ramam spectrum, X-ray diffraction spectrum and FT-IR spectrum. Results shown that: All kinds of the silk fibroins were crystal high polymer composing with the major conformation of β-fold (SilkII). The crystallization degree of Bombyx mori silk fibroin and the nature yellow silk fibroin were higher than the wildly silkworm silk fibroin, and the crystalline structure of the nature yellow silk fibroin was more close to Bombyx mori silk fibroin.
Fibroin
Sericin
Bombycidae
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Fibroin
Bombyx
Sericin
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An octapeptide, GAGAGAGY, was obtained by a novel method, i.e. hydrolysing Bombyx mori silk fibroin. Afterward, a dodecanoic acid-peptide conjugation was synthesized. This amphiphile assembled into cylindrical nanofibers of planar β-sheets at pH 9 and twisted β-sheets at pH 4.
Fibroin
Bombycidae
Sericin
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Sericin
Fibroin
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In insects, the activity of phenoloxidase increases near the site of injury where it not only helps in wound healing but also prevents infection. The present study discusses the regulation of phenoloxidase by age dependent mechanical injury in the silkworm. The experiment was conducted on 4th and 5th instar silkworms with single and multiple wounding. A drastic increase in the enzyme activity was observed in 4th instar caterpillars upon a single wounding. Conversely, less enzyme activity was observed in 5th instar caterpillars upon single wounding but this increased with multiple wounding. This reveals the age dependent control over phenoloxidase activity in silkworm that may be essential in the later instars to prevent any autoimmune effect caused by the enzyme. Controlling enzyme activity may be a significant evolutionary strategy adapted by the caterpillar to regulate the energy investment during 5th instar. The results of the present study confirm the probability of the presence of a novel mechanism which regulates the activity of phenoloxidase in caterpillars at different instars.
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The silk I structure (the structure of Bombyx mori silk fibroin before ginning in the solid state) was determined with 13C two-dimensional (2D) spin-diffusion solid-state NMR, rotational echo double resonance (REDOR) and quantitative use of 13C CP/MAS NMR chemical shifts. We used 13C - 13C double labeled and 13C - 15N double labeled model peptides, (AlaGly)15 in silk I form for solid state NMR analyses. The structure was determined to a repeating type II β-turn. The solubility of B. mori silk fibroin in water was examined in the light of the presence of Tyr and Val residues in the repetitive domains of GAGAGYGAGAG and GAGVGYGAGAG sequences. The presence of amorphous domains, TGSSGFGPYVANGGYSGYEYAWSSESDFGT was also considered as the origin of the solubility of silk fibroin in water. The solution structure of silk fibroin in B. mori silkworm is also discussed with previous circular dichroism (CD), optical rotatory dispersion (ORD) and solution NMR data.
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Bombycidae
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