蠶絲和蜘蛛絲纖維：從溶解性蛋白到超級纖維

1、Silk: From Soluble Protein to Extraordinary FiberJiang Yanke2012-02-02#Silk: From Soluble Protein to Extraordinary Fiber1. Spider silk2. Silkworm silk3. The formation of extraordinary fibers from soluble protein#Examples of silk fibers produced by silkworms and spiders and a schematic illustration.#

2、Fibers produced by silkworms and spiders are natural composites#1. Spider silk The properties of spider silk The category of spider silk The structure of spider silk#The properties of spider silk Extremely high mechanical stability Dragline silk is five times tougher than steel by weight and even th

3、ree times tougher than man-made synthetic fibers, such as Kevlar 49. Supercontraction “Worn-out” silk threads within a spiders net are renewed in the morning dew, and the web regains its rigidity. Biocompatibility, smoothness and thinness in comparison to other available materials#The mechanical pro

4、perties of animal silks in comparisons to other man-made and natural materials#The category of spider silkSeven sets of silk-producing glands in which the constituent silk proteins are synthesized by epithelial cells before being spun as seven different types of silk, each possessing different funct

5、ional properties.#Spider silk#Spider silkThe two most important silks (major ampullate and flagelliform silk fibers) in orb webs spun by Araneus diadematus spiders.#Major ampullate silkCore-shell type structure of silk fibersScanning electron microscopy image of spider silk taken from a web of the g

6、arden spider Araneus diadematus.#2. Silkworm silk Properties Silk protein Applications#The properties of silkworm silk Native silk fiber from Bombyx mori silkworm is known as important biomaterials in many applications including biomedical sutures, tissue engineering scaffolds for tendon, bone, teet

7、h, ligaments and other bioengineered clinical products characteristic strength, moisture absorbance and luster Shortcomings as they are prone to photoyellowing, and have poor rub resistance and wrinkle recovery Its good mechanical strength, water stability, thermal properties, surface roughness and

8、biocompatibility.#Composite materials based on silk proteinspMan-made composite materials based on silk proteins and synthetic polymersNon-biodegradable synthetic polymers: carbon nanotubes, nylon, poly(acrylamide), poly(acrylonitrile), poly(epoxides) et. al.Biodegradable synthetic polymers: poly(as

9、partic acid), poly(-caprolactone), poly(lactic-co-glycolic acid), poly(lactic acid), poly(urethane) pellethane et. al.pMan-made composite materials based on silk proteins and biopolymersPolysaccharides: alginate, cellulose, chitin, cellulose xanthate, chitosan, hyaluronic acidOther proteins: collage

10、n, enzymes, gelatin, green fluorescent protein, growth factors,fibroins of different species, keratin, sericin, spidroins of different species.pMan-made composite materials based on silk proteins and inorganic particlesMetal nanoparticles: Silver nanoparticles, Gold nanoparticles, Transition metal o

11、xides/sulfidesBiominerals: Calcium carbonate, Calcium phosphate, Silica#Applications of composite materials based on silkproteinspTextilesSynthetic polymers: Mixing B. mori fibroin with poly(acrylonitrile) notably improved the fibers water absorption and reduced their tendency to collect static elec

12、tricityBiopolymers: Fibers composed of 30 wt% B. mori fibroin and 70 wt% cellulose had improved elastic moduli at the expense of breaking strength and yield stress relative to equivalent fibers produced solely from celluloseMetal nanoparticles: B. mori fibroin coated with silver nanoparticles to pre

13、vent the growth of the grampositive bacterium Staphylococcus aureus on the surface of the silk fabricpSutures and dressings for woundsTheir strength, biocompatibility and low immunogenicity.Sutures, wound dressings, tissue scaffolds, biocompatible coatings, drug deliverypMaterials with novel electro

14、nic, magnetic and optical propertiespEnzymatically active biomaterials-biosensors#Silk protein from silkworms Fibroin The water-insoluble protein, from mulberry silkworm, has been recognized as a substrate for growth and adherence of cells in culture Sericin The water-soluble component of silk, from

15、 the mulberry silkworm, is used as a biomaterial due to its antibacterial and UV resistant properties Sericin is also reported to suppress in vitro lipid peroxidation and possesses antitumor properties with no immunogenicity Indeed, sericin has previously been reported to possess photoprotective eff

16、ect against UVB-induced acute damage and colon carcinogenesis.#Silk fibroin Heavy (H) fibroin chain 5,236 residues 391kDa Light (L) fibroin chain 266 residues 28kDa P25 glycoprotein two forms differing by glycosylation H-fibroin, L-fibroin, and P25 are assembled in elementary secretory units in the

17、ratio 6:6:1 H-L fibroin are linked by a single disulfide bond between cysteine residues in the C-termini of each of these proteins. P25 associates with the H-L complex primarily by hydrophobic interactions.#L-fibroin is predominantly hydrophobic but formation of an internal disulfide loop and the di

18、sulfide bond to H-fibroin are likely to expose the hydrophilic N-terminus of the molecule. Glycosylation of this part of L-fibroin in P. xuthus further increases hydrophilicity.P25 consists of alternating hydrophobic and hydrophilic areas with considerable number of charged residues. The solubility

19、of mature protein is enhanced by glycosylation.Analysis of known H-fibroins indicates that the nature of interacting motifs, which determine the secondary protein conformation, is crucial, but the mode of motif dispersion in higher order repeats and the regularity of both short and long reiterations

20、 are also of importance.#3. The formation of extraordinary fibers from soluble protein Structure of spider silk proteins Structure of silkworm silk proteins Spinning process of silkworms and spiders#The primary structure of spider silk proteinsStructural modules in Nephila clavipes spider silk prote

21、ins#Primary amino acid sequences for N. clavipes MaSp1 and MaSp2, the two proteins that make up Ma silk. Colored Ala (red), Gly (blue), and Ser (green) represent -sheet structure.#The secondary structure of spider silk proteins # The secondary structure of spider silk proteins consists of up to 3 di

22、fferent structural motifs:p a -spiral similar to a -turn composed of multiple varying GPGXX motifs where X varies between or within proteins and is responsible for the elasticity of the fibersp crystalline -sheet domains rich in alanines (polyalanine stretches of mainly 410 residues)p helical struct

23、ure composed of 3 amino acid repeats of GGX. These motifs also appear to be conserved among proteins of from the same silk gland as well as among many species#The 3D structure of spider silk proteinStructural and conserved features of spidroin N-terminal domain.#The 3D structure of spider silk prote

24、inOverlay of the 20 best-energy structures of the C-terminal NR domain of ADF-3 having a root mean square deviation (r.m.s.d.) of 0.18.#Schematic structure of spider silk from nanoscaleto macroscale.#H-fibroin N-terminusThe primary structure of silkworm silk H-fibroinC-terminus #Deduced amino acid s

25、equence of B. mori H-fibroin. (The representative sequence between residues 1619 to 2642) Crystalline region GAGAGS motifs occupies most of the repeat length, but close to the repeat end, it is interrupted by a Tyr-rich sequence(GAGAGY) that is mostly 21 residues long. When extrapolated to H-fibroin

26、, these data suggest that long GAGAGS iterations harbor inherent limits to the crystal size.#Molecular models of Silk IIWide Angle X-ray ScatteringSilk fibers#Spinning process of silkworms and spidersThe fiber properties would not only result from the amino-acid sequence, but also depending on the a

27、ccidents of processing. The drawing process, rather than primary sequence, exerts the dominant influence on crystallinity in the fibers.The properties of silk formed naturally are the same as those of silk spun synthetically from the same proteins in solution (Trabbic and Yager). (Macromolecules 199

28、8, 31, 462)Silk fibres produced by artificial reeling are superior to those that are spun naturally. (Nature 2001, 410, 541) #The formation of spider fibers from soluble protein#The formation of silkworm silk protein During the fifth instar, a large amount of silk fibroin is synthesized in posterior

29、 silk gland (PSG) cells. The fibroin then moves to the middle silk glands where sericin is added, and finally forms the silk fibers in the anterior silk glands. Abundant sericins include sericin P (150 kDa), sericin M (400 kDa) and sericin A (250 kDa) identified in the distal, central and anterior m

30、iddle silk gland sections, respectively. Silk fibers are of continuing interest to the scientific community because of their impressive mechanical properties. When controllably spun, the mechanical properties of Bombyx mori fibers (strength: 1 GPa, failure strain: 20%) have been shown to be nearly as impressive spider dragline silk.#Schematic diagram of the silk gland of the larvae of the silkworm, Bombyx mori, showing the divisions in the gland, and the pH and the states of the silk fibroin.#States of liquid silk fibro