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From 2010.igem.org

Spider Silk

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 et al 2000