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From 2013.igem.org

Silk protein

The spider silk protein is a fibrous protein. It does not have a folded state on its own; it is able to assemble (multimerize) with multiple identical proteins to form the silk. The protein consists of roughly 3 motifs, each featuring a particular secondary structure in the assembly (table 1) (ref 11 paper recomb biomaterials).

Depending on the processing of the silk proteins, it can have a degree of these secondary structures, defining its properties (table 1). This characteristic of the silk proteins will be discussed in detail in the ‘Silk protein’(link) section.

Amino acid sequence	Secondary structure	Properties
AAAAAAAA	β-sheet	Tensile strenght, rigidity, hydrophobicity
GPG(AG)QQ / GPG(SGG)QQ / GPGGX	β-spiral / β-turn	Extensibility, elasticity
GGX	310 helix	Link, alignment, flexibility

In order to make the silk material a large amount of these proteins are required. The protein has a very repetitive nature (fig. X), with these motifs (table 1) recurring within the protein. This is difficult to produce, because it requires presence of the same tRNAs in a large amount. This can be solved with codon optimization. See ‘Codon optimization’ (link) at the modelling section for the explanation of this approach.