Spider silk

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Spider Silk

File:Spider Web

Spider silk is comparable in strength to carbon fibres
Highly structured at the nanometre scale – not good for synthetic materials
Repetitive structures- GXG motif
Glycine rich segments – hard and soft segments alternating
Hard= hydrogen bonding cross-linked crystallites (polyalanine) forming an amorphic beta sheet structure,
Soft= flexibility (Glycine rich)
Major protein from Nephila clavipes – MaSP1 tandem variants of
MaSP2 also has a repetitive structure – difference soft segment contains proline containing pentamers: The consensus repeat is _GPGGY GPGQQ.3GPSGPGS A8. Similar structure to Elastin – elastic properties of drag-line by the folding of pentamer structure.
In the spider – silk in 3 phases
1) Extremely viscous (withstand shear forces inside spider),
2) Liquid crystallite lower viscosity (near exit duct/glycine rich may be involved),
3) Insoluble fibre (result of dehydration and drawing).
MaSP1 and MaSP2 – Drag line
MaSP2- Glue silk only
Neither- Cocoon silk
Super contraction associated with pentamer motif when wet: low visco-elasticity
Mimic natural proteins or simplify – Mimic structural significance still uncertain for some sequences
DPB1- Optimised for B.subtilis
B.subtilis potential host as simple secretion system compared to yeast. Secretion has advantages over expression in E.coli however; insufficient proportion of protein was secreted by yeast.
Fahnestock, S. R., Yao, Z., & Bedzyk, L. a. (2000). Microbial production of spider silk proteins. Journal of biotechnology, 74(2), 105-19. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/11763501.