The correlation between the length of repetitive domain and mechanical properties of the recombinant flagelliform spidroin

Abstract

Spider silk is an attractive biopolymer with numerous potential applications due to its remarkable characteristics. Among the six categories of spider silks, flagelliform (Flag) spider silk possesses longer and more repetitive core domains than others, therefore performing the highest extensibility. To investigate the correlation between the recombinant spidroin size and the synthetic fiber properties, four recombinant proteins with different sizes [N-Scn-C (n=1-4)] were constructed and expressed using IMPACT system. Subsequently, different recombinant spidroins were spun into fibers through wet-spinning via a custom-made continuous post-drawing device. Mechanical tests of the synthetic fibers with four parameters (maximum stress, maximum extension, Young's modulus and toughness) demonstrated that the extensibility of the fibers showed a positive correlation with spidroin size, consequently resulting in the extensibility of N-Sc4-C fiber ranked the highest (58.76%) among four fibers. Raman data revealed the relationship between secondary structure content and mechanical properties. The data here provide a deeper insight into the relationship between the function and structure of Flag silk for future design of artificial fibers.

Keywords: Fiber structure; Flagelliform silk; Mechanical properties; Synthetic fiber; Wet-spinning.

Fig. 1.

The amino acid sequence of the flagelliform silk protein Sc (the sequence was shown in one character codon). Two rich valine blocks are shown on underline.

Fig. 2.

Purification of the recombinant spidroin. (A) Mechanism of the purification system. Asterisks indicate the modified intein which can be induced N-cleavage by DTT. (B) SDS-PAGE of the purified protein. The silk precursor proteins and purified proteins were indicated by circles and arrows, respectively. B, before cleavage sample; C, the cleavage products: target protein. (C) The molecular weight and the Gly content of the recombinant spidroin.

Fig. 3.

Post-treatment of the spun fiber. (A) Continuous post-drawing device. (B) The SEM (scanning electronic microscope) of the spun fiber and post-treatment fiber of N-Sc1-C. Scale bar: 10 μm.

Fig. 4.

The inner morphology of the synthetic fibers by SEM under different amplifications. Scale bars: 3 μm in A; and 2 μm in B.

Fig. 5.

The mechanical properties of the synthetic fibers. (A) The stress-strain curves show the traditional features of one of each type of fiber, the embedded chart illustrates the enlargement of the rectangular region (indicated by orange dotted line) of the stress-strain curves. (B) The embedded bar chart illustrates the summary of at least 10 sample testing results. Error bars indicate the standard deviation.

Fig. 6.

Raman spectra of the synthetic fibers. The amid І was divided into five peaks via Peak fit software. The charts show the Raman spectra of one of each type of fiber in amid І region. Experimental spectrum, fitting spectrum and the divided spectrum were showed in different colors.