Spider silks molecular structure

Beek, J. D.v., Hess, S., Vollrath, F., and Meier, B. H. (2002). The molecular structure of spider dragline silk Folding and orientation of the protein backbone. Proc. Natl. Acad. Sci. USA 99, 10266-10271. 

Although much of the interest in biological nanostructures has focused on relatively complex functionality, cells and organisms themselves can be considered as a collection of self-assembled materials lipid bilayers, the extracellular matrix, tendon and connective tissue, skin, spider silk, cotton fiber, wood, and bone are all self-assembled biological materials, with an internal structure hierarchically ordered from the molecular to the macroscopic scale. 

Although the amino acid sequence as well as the secondary structure of fibroin differs from those of spidroin, the fibers spun from these proteins, that is, silkworm silk and spider silk have comparable mechanical properties. These may be attributed to the structural characteristics, both at the molecular and filament level. The superior mechanical properties of silk-based materials, such as films, coatings, scaffolds, and fibers produced using reconstituted or recombinant silk proteins, are determined by their condensed structures. 

The properties of spider silk reflect its interna] molecular structure. All such silk is made of protein, but spiders produce a variety of proteins with which to spin it. Proteins are built of amino acids, but the specific properties of a protein are determined by the variety of amino acids that join together to form the protein chain. Scientists have found six amino acids — namely, glycine, alanine, proline, tyrosine, serine, and glutamine — in spider silk. Chains that have long sequences of alanine units can pack together very closely in what we call beta-sheets,... 

Nature uses self-assembly to build highly structured systems for specific functions. Examples include the transfer and storage of genetic information in nucleic acids, the organization of lipids into protective cell membranes that serve as molecular receptors for the cell, and the hierarchical structure of spider silk, still one of the strongest known fibrous materials.yet flexible enough to absorb the impact energy of an unlucky fly. 

Spider silk is composed of large polypeptides, 250-320 kDa. A 285 kDa protein from the spider Nephila clavipes was generated in E. coli and purified. Its structural properties were superior to smaller-molecular-weight proteins. The glycine-rich (44% of residues) protein was generated by increasing the pool of glycyl-tRNA [142]. 

Insect and spider silks are natural biopolymers whose molecular structure enables their use in applications requiring exceptional strength and flexibility of the material. These traits along with their biocompatibility, biodegradability, and the ability to produce large amounts of the material make the use of silk and silk-based biomaterials a rational choice for a host of tissue engineering applications. 

Figure 5.16 Similar molecular structure and aggregate structure between SMPF and spider silk. A hydrogen-bonded hard segment and soft segment form a microphase separated microstructure with a crystalline hard domain and an amorphous soft phase. The amorphous phase and crystalline phase are partially oriented. Source [10] Reproduced with permission from the Royal Society...

Hayashi, C.Y. and Lewis, R.V., Evidence from flageUiform silk cDNA for the structural basis of elasticity and modular nature of spider silks. Journal of Molecular Biology, 1998, 275(5) 773-784. 

Vollrath, F., Strength and structure of spiders silks. Reviews in Molecular Biotechrwlogy, 2000, 74 67—83. 

Structural proteins such as collagen, elastin, and spider silk contain repeating sequences of amino acids. In 1983, Waite discovered that the protein secreted by the phenol gland of the blue sea mussel Mytilus edulis consists of closely related decapeptide and hexapeptide sequences with a combined molecular weight of approximately 130 kilodaltons (kDa).i He further elucidated that this protein is transformed into glue through enzymatic oxidation to form the adhesive plaques that anchor the mussel... 

Micro-diffraction techniques have been developed mainly at the ID 13 beamline of the European Synchrotron Radiation Facility (ERSF) with a beam size of 3-10 pm for viscose rayon fibers, spider silk, spherulites of P(3HB), and a poly(lactic acid)/(atactic-P(3HB)) blend. Recently, we developed the micro-diffraction techniques with 0.5 pm beam size for analysis ultra-high-molecular-weight-P(3HB) mono-filament ° and P(3HB) copolymer spherulites. To reveal the detail fiber structure and the distribution of two types of molecular conformations in drawn P(3HB-co-8%-3HV) mono-filament, a micro-beam X-ray diffraction experiment was performed with synchrotron radiation at SPring-8, Japan. The beam size was focused to 0.5 pm with the Fresnel Zone Plate technique and the P(3HB-co-8%-3HV) mono-filament was scanned linearly perpendicular to the fiber axis with a step of 4 pm. 

Hayashi C.Y. and Lewis R.V., Spider flagelUfotm silk Lessons in protein design, gene structure, and molecular evolution, BioEssays, 23, 750, 2001. 

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