Biochemical mechanism involved in the enhancement of the Young's modulus of silk by the SpiCE protein

초록

Silk fibers are known for their superior mechanical properties, with the strongest possessing over seven times the toughness of kevlar. Recently, low molecular weight non-spidroin protein, spider-silk constituting element (SpiCE), has been reported to enhance the mechanical properties of silk; however, its specific action mechanism has not yet been elucidated. Here, we explored the mechanism by which SpiCE strengthened the mechanical properties of major ampullate spidroin 2 (MaSp2) silk through hydrogen bonds and salt bridges of the silk structure via all-atom molecular dynamics simulations. Tensile pulling simulation on silk fiber with SpiCE protein revealed that the SpiCE protein enhanced the Young's modulus by up to 40% more than that of the wild type. Bond characteristic analysis revealed that SpiCE and MaSp2 formed more hydrogen bonds and salt bridges than the MaSp2 wild-type model. Sequence analysis of MaSp2 silk fiber and SpiCE protein revealed that SpiCE protein contained more amino acids that could act as hydrogen bond acceptors/donors and salt bridge partners. Our results provide insights into the mechanism by which non-spidroin proteins strengthen the properties of silk fibers and lay the groundwork for the development of material selection criteria for the design of de novo artificial silk fibers.

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