Types+of+spider+silk

== The many unique characteristics of spider silk can be attributed to the different types of spider silk. The variety of the silk comes from the ability of the spider to produce different qualities of silks for different uses in their biological environment. The common silks produced in most arachnids include, major-ampullate silk, capture-spiral silk, tubuliform silk, aciniform silk and minor ammuplate silk. Though due to the extensive time it takes to produce mass amounts of this precious silk, recent science has developed alternative methods to harvesting artificial spider silk and other silk-like high performance materials.

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=**__Major-Ampullate Silk__** = Major-ampullate silk, commonly referred to as dragline silk, is a high performance fiber with mechanical properties that carries unusual strength, about 50% stronger then the other silk fibers, however it lack extensibility.  The ecological function of dragline silk is to provides a dry frame for orb webs that supports the sticky capture-spiral silk, and together they resist kinetic energy of incoming flying insect [1] . Recent research has hypothesized the mechanical performance of dragline and minor-ampullate  silk are qualitatively more similar to one another than to the other silks as they are both comprised of molecular models of silks fibroins that contain a large number of poly-Ala or Gly-Ala amino acid sequence motifs [2]. Blackledge et al. (2006) published his hypothesis, that due to the higher frequency of poly-Ala motifs in major-ampullate fibers, they form an exceptionally strong crystalline secondary/tertiary structure, which provides insight on the greater strength and decreased extensibility of dragline relative to minor-ampullate silk [3]. They support their assumptions with previous research that emphasizes the association of the prevalence of poly-Ala motifs in major-ampullate silk with high tensile strength [4].

=**__Capture-Spiral Silk__** = Support  ed by the dry major-ampullate silk of orb webs, capture-spiral silk performs together with dragline to absorb kinetic energy of flying insects.  Capture-spiral silk is  coated with an aqueous glue devised of <span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">high concentration of positively charged organic amines and diamines, and also glycoproteins rich in N-acetylgalactosamine which give the distinctive quality of being sticky [5] .Though the structure of this silk remains undetermined, a main protein in capture-spiral silk was discovered to be flagelliform protein, whose molecular and supramolecular structures have been derived. <span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;"> It is stretchier than most silks; found to be an order of magnitude stretchier and 1000 times more compliant than dragline silk [6]. Hayashi et al. (1998) proclaims that the long uninterrupted runs of Gly-Pro-Gly containing motifs in flagelliform fibroins may explain much of the extreme extensibility of the capture spiral silk. They are hypothesized to form successive b-turns that perform as molecular springs, which are characterized by GPPGX<span style="font-family: 'Times New Roman',Times,serif; font-size: 8px;">n <span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">motifs [4] [7] <span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;"> Tests have confirmed that the capture-spiral silk has shown poor results at storing energy, while studying the viscoelastic behavior of polymers, due to the weaker intermolecular interactions relative to dragline fibroin [8]. Denny et al. (1976) found that the extremely high compliance and extensibility of capture-spiral silk aids in the gradual deceleration of impacting insects by “cradling” so that the prey do not bounce out of the web. During this process, the kinetic energy of the insect is absorbed low initial resilience of both capture-spiral and major-ampullate silk[1] <span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">.

=<span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">**__Tubuliform Silk__** = <span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">Tubuliform silk is unique in the sense that it is only produced by the female spider once in their lifespan. Also known as egg case silk, tubuliform silk possess the highest stiffness out of all the dry spider silks, and is therefore the weakest. It’s molecular structure is composed of very long, complex repeats instead of a short simple repeat much like the other silks <span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">[3]. The fibroins in tubuliform consist of unique high serine and low glycine content which formulates the structure into both an a-helix and disordered conformation as revealed by circular dichroism and infrared spectroscopy [9]. Good biocompatibility and low biodegradability of egg case silk are an advantage for use in biomaterial applications [10].

=<span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">**__Aciniform Silk__** = <span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">The biological function of aciniform silk is used to preserve prey by using the silk to mummify the insect and well as providing an added layer of protection for the egg sac [3]. The dry aciniform silk is the most resilient of all the spider silks due to its high strength and extensibility. It’s molecular structure has been investigated by Hayashi et al. (2004) and results exhibit that it is composed of highly homogenized repeats that are 200 amino acids in length with a prevalence of poly-serine and threonine and a low percentage of glycine and alanine. However due to the little data obtained on the molecular structure of aciniform, the secondary structure has still yet to be characterized. Mechanical data however suggests that the greater performance of the aciniform fibroin must indicate that the structure is not composed of simple repeats of alanine and/or glycine rich motifs much like the other dry silks [11].

=<span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">**__Minor-Ampullate Silk__** = <span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">Minor-ampullate silk share many similarities with dragline silk, both containing glycine and alanine rich motifs that form crystalline b-sheets. However minor-ampullate possesses qualities of high modulus and extensibility, and moderate tensile strength and toughness. In biological settings the spiders use this silk to temporarily build a structure of the orb web, as well it is added to dragline silk to improve structural soundness of the orb web [3].

<span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">[1] Denny, M. (1976). Physical properties of spider silks and their role in design of orb-webs. J. Exp. Biol. 65,483 -506.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">[2] Blackledge, T. A., Swindeman, J. E. and Hayashi, C. Y. (2005c). Quasistatic and continuous dynamic characterization of the mechanical properties of silk from the cobweb of the black widow spider Latrodectus hesperus. J. Exp. Biol. 208,1937 -1949.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">[3] Blackledge, T. A., Hasyashi, C. Y. (2006) Silken toolkits: biomechanics of silk fibers spun by orb web spider Argiope Argentata (Fabricius 1775). J. Exp. Biol. 209, 2452-2461.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">[4] Hayashi, C. Y. and Lewis, R. V. (1998). Evidence from flagelliform silk cDNA for the structural basis of elasticity and modular nature of spider silks. J. Mol. Biol. 275,773 -784.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">[5] Vollrath, F. & Tillinghast, E.K. (1991) Glycoprotein glue beneath a spider web's aqueous coat. Naturwissenschaften 78, 557–559.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">[6] Köhler, T. and Vollrath, F. (1995). Thread biomechanics in the two orb-weaving spiders Araneus diadematus (Araneae, Araneidae) and Uloborus walckenaerius (Araneae, Uloboridae). J. Exp. Zool. 271, 1-17.

<span style="background-color: white; font-family: 'Times New Roman',Times,serif; font-size: 16px;">[7]Becker, N., Oroudjev, E., Mutz, S., Cleveland, J.P., Hansma, P.K., Hayashi, C.Y., Makarov, D.E., and Hansma, H.G. (2003) Molecular nanosprings in spider capture-silk threads. Nature Publishing Group. Vol 2, 278-283.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">[8] Dicko, C., Knight, D., Kenney, J. M. and Vollrath, F. (2004). Secondary structures and conformational changes in flagelliform, cylindrical, major, and minor ampullate silk proteins. Temperature and concentration effects. Biomacromolecules 5,2105 -2115.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">[9] Lin, Z., Huang, W., Zhang, J., Fan, J. S., Yang, D. (2009) Solution structure of eggcase silk protein and its implications for silk fiber formation. PNAS. Vol 106 no. 22, 8906-8911.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">[10] Gellynck K, et al. (2008) Biocompatibility and biodegradability of spider egg sac silk. J Mater Sci: Mater Med 19:2963–2970.

<span style="font-family: 'Times New Roman',Times,serif; font-size: 16px;">[11] Hayashi, C. Y., Blackledge, T. A., Lewis, R. V. (2004). Molecular and Mechanical Characterization of Aciniform Silk: Uniformity of Iterated Sequence Modules in a Novel Member of the Spider Silk Fibroin Gene Family. Mol Biol Evol. 21(10):1950-9.