H-fibroin

Bombyx Cocoon mori Heavy, light chains fibroins and P25 (6-6-1) (GAGAGS)5 15 / -sheet (GX)5 i5 / -turns/helices GAAS spacer Gly (43), Ala (30), Ser (12), SSC (85), PC (23) Low-concentration H-fibroin disorder/PPII / fi-tum type II silkl) High -concentration helical / -Sheet (silk II) 40-50 10-20... 

The core filament of B. mori silk, fibroin, is composed of a heavy chain fibroin (H-fibroin, 391 kDa) and a light chain fibroin (L-fibroin, 28 kDa), as well as P25 protein (25 kDa). These three constituents assemble into the secretory units in the ratio of 6 6 1 (H L P25) (Inoue et al., 2000 Shimura et al., 1976). H-fibroin and L-fibroin link together via a disulfide bond and the P25 is thought to act as a kind of chaperon to assist the transport and secretion of the insoluble H-fibroin (Sehnal and Zurovec, 2004 Tanaka et al., 1999 Zhou et al., 2000). H-fibroin has a much higher molecular weight and takes up 90% weight of the core filament. The properties of the core filament are mainly attributed to H-fibroin, which is often referred to as fibroin. 

Figure 14.9 Spicier fibers are composite materials formed by large silk fibroin polypeptide chains with repetitive sequences that form p sheets. Some regions of the chains participate in forming 100-nm crystals, while other regions are part of a less-ordered mesh-work in which the crystals are embedded. The diagram shows a model of the current concepts of how these fibers are built up, which probably will be modified and extended as new knowledge is gained. (Adapted from F. Vollrath, Sci. Am. p. 54-58, March 1992 and A.H. Simmons, Science 271 84-87, 1996. Photograph courtesy of Science Photo Library.)...

Y.H. Wu, Q.C. Shen, and S.S. Hu, Direct electrochemistry and electrocatalysis of heme-proteins in regenerated silk fibroin film. Anal. Chim. Acta 558, 179-186 (2006). 

Asakura, T., Suzuki, H., and Watanabe, Y. (1983). Conformational characterization of silk fibroin in intact Bombyx mod and Philosamia cynthia ricini silkworms by 13C NMR spectroscopy. Macromolecules 16, 1024—1026. 

Asakura, T., Kuzuhara, A., Tabeta, R., and Saito, H. (1985). Conformation characteriz-tion of Bombyx mod silk fibroin in the solid state by high-frequency 13C cross polarization-magic angle spinning NMR, x-ray diffraction, and infrared spectroscopy. Macromolecules 18, 1841-1845. 

Asakura, T., Yoshimizy, H., and Yoshizawa, F. (1988). NMR of silk fibroin. 9. Sequence and conformation analysis of the silk fibroins from Bombyx mod and Philosamia cynthia ricini by 15N NMR spectroscopy. Macromolecules 21, 2038-2041. 

Fossey, S. A., Nemethy, G., Gibson, K. D., and Scheraga, H. A. (1991). Conformational energy studies of beta-sheets of model silk fibroin peptides. 1. Sheets of poly(Ala-Gly) chains. Biopolymers 31, 1529-1541. 

Ha, S. W., Gracz, H. S., Tonelli, A. E., and Hudson, S. M. (2005). Structural study of irregular amino acid sequences in the heavy chain of Bombyx mori silk fibroin. Biomacromolecules 6, 2563-2569. 

Hepburn, H. R., Chandler, H. D., and Davidoff, M. R. (1979). Extensometric properties of insect fibroins The green lacewing cross-/ , honeybee a-helical and greater wax-moth parallel-/ conformations. Insect Biochem. 9, 69-77. 

Inoue, S., Tanaka, K., Arisaka, F., Kimura, S., Ohtomo, K., and Mizuno, S. (2000a). Silk fibroin of Bombyx mori is secreted, assembling a high molecular mass elementary unit consisting of H-chain, L-chain, and P25, with a 6 6 1 molar ratio./. Biol. Chem. 275, 40517-40528. 

Inoue, S., Kobayashi, M., Tanaka, T., Tsuda, H., Magoshi, Y., and Magoshi, J. (2001). Atomic force microscopy on fibroin molecules and its aggregates. Abstr. Pap. Am. Chem. Soc. 221, 261-PMSE. 

Kameda, T., Ohkawa, Y., Yoshizawa, K., Nakano, E., Hiraoki, T., Ulrich, A. S., and Asakura, T. (1999). Dynamics of the tyrosine side chain in Bombyx mori and Sarnia cynthia ricini silk fibroin studied by solid state H-2 NMR. Macromolecules 32, 8491-8495. 

Lazo, N. D., and Downing, D. T. (1999). Crystalline regions of Bombyx mori silk fibroin may exhibit beta-turn and beta-helix conformations. Macromolecules 32, 4700-4705. Lee, K. H. (2004). Silk sericin retards the crystallization of silk fibroin. Macromol. Rapid Commun. 25, 1792-1796. 

Sezutsu, H., and Yukuhiro, K. (2000). Dynamic rearrangement within the antheraea pernyi silk fibroin gene is associated with four types of repetitive units. J. Mol. Evol. 

Sonoyama, M., Miyazawa, M., Katagiri, G., and Ishida, H. (1997). Dynamic FT-IR spectroscopic studies of silk fibroin films. Appl. Spectrosc. 51, 545-547. 

Yang, Y. H., Shao, Z. Z., Chen, X., and Zhou, P. (2004). Optical spectroscopy to investigate the structure of regenerated Bombyx mori silk fibroin in solution. Biomacromolecules 5, 773-779. 

Silk is produced from the spun threads from silkworms (the larvae of the moth Bombyx mori and related species). The main protein in silk, fibroin, consists of antiparallel pleated sheet structures arranged one on top of the other in numerous layers (1). Since the amino acid side chains in pleated sheets point either straight up or straight down (see p. 68), only compact side chains fit between the layers. In fact, more than 80% of fibroin consists of glycine, alanine, and serine, the three amino acids with the shortest side chains. A typical repetitive amino acid sequence is (Gly-Ala-Gly-Ala-Gly-Ser). The individual pleated sheet layers in fibroin are found to lie alternately 0.35 nm and 0.57 nm apart. In the first case, only glycine residues (R = H) are opposed to one another. The slightly greater distance of 0.57 nm results from repulsion forces between the side chains of alanine and serine residues (2). 

Liu H, Liu Y, Qian J, Yu T, Deng J. Feature of entrapment of glucose oxidase in regenerated silk fibroin membranes and fabrication of a L -dimethylferrocene-mediating glucose sensor. Microchemical Journal 1996, 53, 241-252. 

Cao, H. "Preparation of Silk Fibroin-based Electrospun Mat and Deposition of Inorganic Mineral on Silk Fibroin Matrix" Ph.D dissertation, Fudan University, 2008... 

Chen, C., Cao, C.B., Ma, X.L., Tang, Y., and Zhu, H.S. "Preparation of non-woven mats from all-aqueous silk fibroin solution with electrospinning method". Polymer 47(18), 6322-6327 (2006a). 

Ha, S.W., Park, Y.H., and Hudson, S.M. "Dissolution of Bombyx mori silk fibroin in the calcium nitrate tetrahydrate-methanol system and aspects of wet spinning of fibroin solution". 

Hu, K., Lv, Q., Cui, F.Z., Feng, Q.L., Kong, X.D., Wang, H.L., Huang, L.Y., and Li, T. "Biocompatible fibroin blended films with recombinant human-like collagen for hepatic tissue engineering". J. Bioact. Compat. Polym. 21(1), 23-37 (2006a). 

Jeong, L., Lee, K.Y., Liu, J.W., and Park, W.H. "Time-resolved structural investigation of regenerated silk fibroin nanofibers treated with solvent vapor". Int. ]. Biol. Macromol. 38(2), 140-144 (2006). 

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