A Step Towards Artificial Synthesis of Spider Silk

Believe it or not, but a spider thread, related to its thickness, is stronger than steel and more elastic than rubber.

It is one of the most expandable, resistant to tearing, and tough materials found in nature.

Being organic and non-toxic, the spider silk would represent the ideal material for a large array of medical and technical applications.

But it is impossible to collect it from spiders, as millions of individuals would offer just some grams of the material, so researchers are highly interested in decoding the secrets behind the spiders' silk synthesis in order to develop a technique imitating this.

A team led by Thomas Scheibel at the Technical University of Munich has found more details of the interaction between hydrophilic (water friendly) and lipophilic (fat friendly) qualities of the silk proteins, crucial in the spinning process, the turn from a solution into a solid thread.

The silk consists of two different proteins.

The German team managed by genetic engineering to synthesize one of the spider silk proteins of the European garden spider (Araneus diadematus).

The dialysis separated two different fluid phases, one of protein dimers (two joined amino acid molecules) and a second one of oligomers (several linked amino acid molecules).

When the researchers added potassium phosphate, a natural catalyst of silk aggregation, the liquid proteins could be pulled into threads.

"It is clearly not a structural change in the protein, but rather the degree of oligomerization that is crucial for thread formation," said Scheibel.

The silk solution in the spider's silk gland displays a high concentration of sodium chloride which turns off oligomer formation and the removal of the salt makes the proteins aggregate into oligomers.

Inside the silk gland, the pH is relatively high (basic, over 7), but within the spinning duct it is low, slightly acid (below 7).

There was no phase separation for the silk protein when the pH was kept basic.

When basic, the normally uncharged tyrosine radicals in the protein are deprotonated, acquiring a negative charge that turns off the interactions between the hydrophobic and lipophilic regions of the proteins, crucial for oligomerization.

"Our insights form a foundation for the establishment of an effective spinning process for the production genetically engineered spider silk," said
Scheibel.