Spider silks outrival natural and many synthetic fibers in terms of their material characteristics. In nature, the formation of a solid fiber from soluble spider silk proteins is the result of complex biochemical and physical processes that take place within specialized spinning organs. Herein, we present natural and artificial silk production processes, from gene transcription to silk protein processing and finally fiber assembly. In-vivo and in-vitro findings in the field of spider silk research are the basis for the design of new proteins and processing strategies, which will enable applications of these fascinating protein-based materials in technical and medical sciences.

The interactions of partially unfolded proteins provide insight into protein folding and protein aggregation. In this work, we studied partially unfolded hen egg lysozyme interactions in solutions containing up to 7 M guanidinium chloride (GdnHCl). The osmotic second virial coefficient (B(22)) of lysozyme was measured using static light scattering in GdnHCl aqueous solutions at 20 degrees C and pH 4.5. B(22) is positive in all solutions, indicating repulsive protein-protein interactions. At low GdnHCl concentrations, B(22) decreases with rising ionic strength: in the absence of GdnHCl, B(22) is 1.1 x 10(-3) mLmol/g(2), decreasing to 3.0 x 10(-5) mLmol/g(2) in the presence of 1 M GdnHCl. Lysozyme unfolds in solutions at GdnHCl concentrations higher than 3 M. Under such conditions, B(22) increases with ionic strength, reaching 8.0 x 10(-4) mLmol/g(2) at 6.5 M GdnHCl. Protein-protein hydrodynamic interactions were evaluated from concentration-dependent diffusivity measurements, obtained from dynamic light scattering. At moderate GdnHCl concentrations, lysozyme interparticle interactions are least repulsive and hydrodynamic interactions are least attractive. The lysozyme hydrodynamic radius was calculated from infinite-dilution diffusivity and did not change significantly during protein unfolding. Our results contribute toward better understanding of protein interactions of partially unfolded states in the presence of a denaturant; they may be helpful for the design of protein refolding processes that avoid protein aggregation.

Am seidenen Faden: Spinnenseiden haben mechanische Eigenschaften, die jene der meisten natürlichen und synthetischen Fasern übertreffen. Wegen der Komplexität des In‐vivo‐Spinnprozesses scheiterte bislang seine Nachahmung durch klassische Spinnmethoden. Die Analyse des natürlichen Prozesses, kombiniert mit Erkenntnissen aus In‐vitro‐Untersuchungen, hilft bei der Entwicklung eines bionischen Spinnverfahrens zur Spinnenseidenherstellung (siehe Bild).magnified imageDie Proteinfaser Spinnenseide ist hinsichtlich ihrer Materialeigenschaften anderen natürlichen und vielen synthetischen Fasern überlegen. In der Natur beruht die Bildung einer festen Faser aus einem löslichen Spinnenseidenprotein auf komplexen biochemischen und physikalischen Prozessen, die in spezialisierten Spinnorganen ablaufen. In diesem Aufsatz wird der natürliche Prozess der Seidenherstellung ausgehend von der Gentranskription über die Proteinverarbeitung bis hin zur abschließenden Faserbildung vorgestellt; ebenso kommen technische Verfahren zur Seidenverspinnung zur Sprache. In‐vivo‐ und In‐vitro‐Befunde auf dem Gebiet der Spinnenseidenforschung bilden die Grundlage für die Gestaltung neuer Proteine und Verarbeitungsstrategien, die die Anwendung dieser faszinierenden proteinösen Materialien in der Technik und der Medizin ermöglichen können.

List of notations FS= forced silking RH = relative humidity % w/v = weight per volume percentage % v/v = volume per volume percentage IntroductionSpider silk produced by orb-weaving spiders reveals fascinating mechanical properties, in particular, its unique combination of high tensile strength and elasticity, distinguishing it from most other natural or man-made fi bers (Cunniff et al., 1994;Denny, 1976;Eisoldt et al., 2011;Gosline et al., 1984Gosline et al., , 1999Heim et al., 2009;Kaplan et al., 1991;Ko and Jovicic, 2004). Of the fi ve different silks produced by an orb-weaving spider for web building, dragline silk, serving as frame and radial fi ber in the web and as the spider's lifeline, is the best characterized one, as it is the easiest accessible one Vollrath, 2000). A common method to obtain dragline silk for mechanical and structural analysis is the application of forced silking of captive spiders, that is, forcibly pulling the fi ber from a spider's spinneret (e.g. by winding it on a rotating mandrel) (Ortlepp and Gosline, 2004;Perez-Rigueiro et al., 2005;Work and Emerson, 1982). Earlier studies have revealed that spinning speeds have an impact on resilience, strain at breaking, breaking energy, initial Young's modulus, yield point and ductility (most likely related to the variation in diameter of a single fi ber; Chen et al., 2006; PerezRigueiro et al., 2005;Romer and Scheibel, 2008;Scheibel, 2004;). Furthermore, it was shown that forcibly silked fi bers have higher storage moduli and lower loss moduli than native silks (Blackledge et al., 2005; Work, 1976). Despite their intriguing mechanical properties, the use of these fi bers in various industrial or medical applications is limited because of constraints in farming of spiders which are based on their territorial and cannibalistic nature (Fox, 1975). Thus, the focus of silk research has recently shifted towards biotechnologically producing the underlying proteins as well as mimicking the spinning process to produce a new class of high-performance fi bers (Hardy et al., 2008;O'Brien et al., 1998;Omenetto and Kaplan, 2010;Scheibel, 2004).Artifi cial spider silk fi bers can be obtained by two different approaches: (a) spinning from regenerated silk dopes and (b) spinning from solutions of recombinant silk proteins. Regenerated silk solutions from silk fi bers are usually prepared by dissolving a large amount of natural silk fi bers in harsh solvents, such as highly concentrated lithium bromide solutions, hexafl uoroisopropanol (HFIP) or hexafl uoroacetone hydrate (Hardy et al., 2008). However, the number of studies on spider silk is limited as most Pages 83-94 http://dx

Spider silk with its intriguing mechanical properties has a high potential for numerous applications in technology and industry. However, the production of silk fibers from regenerated or recombinant silk solutions is as of today limited by the requirement of strong chaotropic agents and chemical postspin treatments, yielding fibers with weaker mechanical properties than their native counterparts. Here, rheological data of regenerated Bombyx mori fibroin and aqueous silk solutions of recombinant spider silk protein eADF3 indicate that the presence of kosmotropic salts, and elevated temperatures result in solution behavior more alike that of a native silk spinning dope. The authors believe that their findings are helpful for the successful silk spinning from recombinant or regenerated silk solutions.

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In the past, we have successfully designed and produced a variety of engineered spider silk-like proteins (eADF3 and eADF4) based upon the primary sequence of the natural dragline proteins ADF3 and ADF4 from the spider Araneus diadematus [1]. Genetically engineered spider silk proteins can be modified at the molecular level to optimize the biochemical and mechanical properties of the final product. Although engineered spider silk proteins can be processed into fibers using different spinning methods, our group is interested in the technical realization of a biomimetic approach. Here, we present an overview over our biomimetic fiber production process.