Secondary Structure Transition and Critical Stress for a Model of Spider Silk Assembly

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Giesa, T., Perry, C.C. ORCID: 0000-0003-1517-468X and Buehler, M.J., 2016. Secondary Structure Transition and Critical Stress for a Model of Spider Silk Assembly. Biomacromolecules, 17 (2), pp. 427-436. ISSN 1525-7797

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Official URL: http://doi.org/10.1021/acs.biomac.5b01246

Abstract

Spiders spin their silk from an aqueous solution to a solid fiber in ambient conditions. However, to date the assembly mechanism in the spider silk gland has not been satisfactorily explained. In this paper, we use molecular dynamics simulations to model N. clavipes MaSp1 dragline silk formation under shear flow and determine the secondary structure transitions leading to the experimentally observed fiber structures. While no experiments are performed on the silk fiber itself, insights from this polypeptide model can be transferred to the fiber scale. The novelty of this study lies in the calculation of the shear stress (300-700 MPa) required for fiber formation and identification of the amino acid residues involved in the transition. This is the first time that the shear stress has been quantified in connection with a secondary structure transition. By study of molecules containing varying numbers of contiguous MaSp1 repeats we identified the smallest molecule size that gives rise to a 'silk-like' structure contains six poly-alanine repeats. Through a probability analysis of the secondary structure we identify specific amino acids that transition from α-helix to β-sheet. In addition to portions of the poly-alanine section these amino acids include glycine, leucine and glutamine. Stability of β-sheet structures appears to arise from a close proximity in space of helices in the initial spidroin state. Our results are in agreement with the forces exerted by spiders in the silking process and the experimentally determined global secondary structure of spidroin and pulled MaSp1 silk. Our study emphasizes the role of shear in the assembly process of silk and can guide the design of microfluidic devices that attempt to mimic the natural spinning process and predict molecular requirements for the next generation of silk-based functional materials.

Item Type:

Journal article

Publication Title:

Biomacromolecules

Creators:

Giesa, T., Perry, C.C. and Buehler, M.J.

Publisher:

American Chemical Society

Date:

2016

Volume:

Number: