Abstract
Spider dragline silk is a remarkable material that shows excellent mechanical properties, diverse applications, biocompatibility and biodegradability. Transgenic silkworm technology was used to obtain four types of chimeric silkworm/spider (termed composite) silk fibres, including different lengths of recombinant Major ampullate Spidroin1 (re-MaSp1) or recombinant Major ampullate Spidroin2 (re-MaSp2) from the black widow spider, Latrodectus hesperus. The results showed that the overall mechanical properties of composite silk fibres improved as the re-MaSp1 chain length increased, and there were significant linear relationships between the mechanical properties and the re-MaSp1 chain length (p < 0.01). Additionally, a stronger tensile strength was observed for the composite silk fibres that included re-MaSp1, which only contained one type of repetitive motif, (GA)n/An, to provide tensile strength, compared with the silk fibres that includedre-MaSp2, which has the same protein chain length as re-MaSp1 but contains multiple types of repetitive motifs, GPGXX and (GA)n/An. Therefore, the results indicated that the nature of various repetitive motifs in the primary structure played an important role in imparting excellent mechanical properties to the protein-based silk fibres. A silk protein with a single type of repetitive motif and sufficiently long chains was determined to be an additional indispensable factor. Thus, this study forms a foundation for designing and optimizing the structure of re-silk protein using a heterologous expression system.
Highlights
The silk of the best known mulberry silkworm, Bombyx mori, is of specific scientific interest because of its industrial-scale production and excellent mechanical properties
To investigate the relationship among protein chain length, repetitive motifs and the mechanical properties of dragline silk, the present study generated four types of composite silk fibres using a silkworm silk-gland bioreactor, including different lengths of re-MaSp1 orre-MaSp2 derived from the corresponding dragline silk proteins of L. hesperus
The MaSp1 gene of L. hesperus only has a single exon of 9,390 base pairs encoding 3,129 amino acids characterized by several highly repetitive units that consist of head-to-tail ligation of four types of primary repetitive sequences, known as Type[1], Type[2], Type[3] and Type[4]
Summary
The silk of the best known mulberry silkworm, Bombyx mori, is of specific scientific interest because of its industrial-scale production and excellent mechanical properties. To investigate the relationship among protein chain length, repetitive motifs and the mechanical properties of dragline silk, the present study generated four types of composite silk fibres using a silkworm silk-gland bioreactor, including different lengths of re-MaSp1 orre-MaSp2 derived from the corresponding dragline silk proteins of L. hesperus. The results showed that the overall mechanical properties of the composite silk fibres improved with an increasing in the chain length of the recombinant silk protein. This indicated that that the existence of various repetitive motifs in the primary structure and the presence of the same type of repetitive motif and a long protein chain in the silk protein were indispensable important factors for the outstanding mechanical properties of silk fibre. Based on our research results, we speculate that if an artificial spider silk gene expressing proteins with longer length is introduced into the composite silk fibre, silk fibres with improved mechanical properties would be generated
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