The formation of silk fibres by both spiders and silkworms is characterized by the conversion of short-range order protein structures into long-range order structures which are rich in protein sheets in the spun material. It has been hypothesized that the interplay of water and biopolymer flexibility is key to this transition.
To test this, we have used quasi-elastic neutron scattering to investigate the effect of hydration on silk protein films that have a structural composition similar to the short-range ordered solution found in the animal. Three main results are apparent: (i) we are able to monitor simultaneously the evolution of structure and dynamics in the protein film; (ii) while both low and high hydration levels prevent structural conversion, intermediate water content promotes conversion to protein sheets; and (iii) high hydration levels are associated with large amplitude motions of the biopolymer chains. This suggests that silk protein conversion may be enabled, or inhibited, via clever control of chain movement.
(a) Effect of increased hydration on the bulk motion (mean square displacement) of silk proteins films. (b) Neutron diffraction spectrum taken before (black) and after (red) conformational change. The Bragg reflection at 4.3 Å is evidence of regular spacing between the strands of the protein sheet structures.
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Contact: Dr. Cedric Dicko, Cedric.email@example.com
C Dicko, I Diddens (Oxford University), AE Terry, MTF Telling (ISIS), F Vollrath (Oxford University)
Research date: March 2009
C Dicko et al., Biomacromolecules 9 (2008) 216
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