Microbial production of amino acid-modified spider dragline silk protein with intensively improved mechanical properties

In this study, a silk protein 11R26 from the dragline silk protein of Nephila clavipes was used to analyze the potential effects of the special amino acids on the function of 11R26. Three protein derivatives ZF4, ZF5 and ZF6 were obtained by site-directed mutagenesis, based on the sequence of 11R26, and among these derivatives, serine was replaced with cysteine, isoleucine and arginine, respectively.

After being expressed and purified the mechanical performance of the fibers derived from the four proteins was tested. Both hardness and average elastic modulus of ZF4 fiber increased 2.2 times compared with those of 11R26. The number of disulfide bonds in ZF4 protein was 4.67 times to that of 11R26, which implied that disulfide bonds outside the poly-Ala region affect the mechanical properties of spider silk more efficiently.