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Team:Newcastle/Spider silk
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Latest revision as of 12:52, 5 July 2010
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Contents |
Spider Silk
Background Info
| World’s strongest spider silk comes from species of the genus Nephila |
| (The golden orb spider: the largest spider in this genus is Nephila maculata) |
| Its impressive web can be up to 6metres long and 2metres wide and last several years. |
| It has long been used by man; tribal people wrapped it around sticks to catch fish. |
| In a modern setting its uses are becoming more and more valuable from parachutes to bullet proof vests and in this |
| project as measure to help fix cracks in concrete. |
| http://www.naturia.per.sg/buloh/inverts/nephila.htm |
 
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| Buy a Nephila |
Major Ampulate Spidroin Proteins
| 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 |
| A GQG GYG GLG SQG A GRG GLG GQG A GA6GGx |
| 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 |
| MaSP1-Auxilary |
| 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 pr}oteins. Journal of biotechnology, 74(2), 105-19. Retrieved from http://www.ncbi.nlm.nih.gov/pubmed/11763501. |
Self Assembly and pH
| Self assembly of Spider silk proteins is controlled by a pH sensitive relay. |
| A drop to pH 6.3 and shearing forces are believes to result in the hard form of spider silk. |
| Miniature spidroins (a few repeats 4repCT) form metre long fibres irrespective of pH. |
| Introduction of N-terminal domain from MASP1 (Euprosthenops australis) |
| to mini spidroins allows self assembly at pH 6.3 and delays aggregation above pH7. |
| Relay- like mechanism N terminal regulates assembly. pH 8 NT-mini spidroins for long firbes over days at pH 6 they form rapidly. |
| C-terminal domain promotes Silk formation by ordering the repetitive segments. |
| Askarieh, G. et al., 2010. Self-assembly of spider silk proteins is controlled by a pH-sensitive relay. Nature, 465(7295), 236-238. Available at: http://www.nature.com/doifinder/10.1038/nature08962. |
