overcoming biological laws
The tensile strength of spider silk fibers is provided by protein segments that are tightly packed and zipped together. Spider silk proteins are secreted from silk gland cells, so they must be devoid of long stretches of hydrophobic residues as such segments become trapped in membranes inside the cell. Also, such hydrophobic residues may mediate tight interactions in protein zippers, attractive features for the generation of artificial solid silk.
Protein production in bacteria can bypass the natural rules that spiders must follow because they lack membranes to trap the proteins in cells. Based on these insights, the researchers designed spider silk proteins that are predicted to produce more robust zippers, and successfully generated a panel of these in bacteria.
Biomimetic spinning of these engineered spider silk proteins resulted in increased tensile strength, and the two fiber types displayed stiffness comparable to native dragline silk. Bioreactor expression and purification resulted in a protein yield of ~9 g/L, in line with the requirements for an economically viable industrial bulk-scale production. The researchers’ proteins from a 1L bacterial culture would be enough to spin a fiber 18km long.
Source: Karolinska Institutet