How Spider Silk Pulls Itself Together

A pair of structural studies have shed new light on how spiders transform a protein fluid into a silk fiber that’s tough as nails. The two independent research teams discovered in lab experiments that spider silk proteins contain molecular switches that respond to changes in ionic composition, flow shear forces, and pH—similar to the changes that occur in a spider’s spinning apparatus. Working with the C-terminal domain of a silk protein from the cross orb-weaver spider, a team led by Horst Kessler of the Technical University of Munich suggests that this domain contributes to the switch between fluid and silk fiber forms in response to changes in salt concentration and mechanical forces (Nature 2010, 465, 239). Meanwhile, researchers led by Stefan D. Knight of the Swedish University of Agricultural Sciences determined that the N-terminal domain of a silk protein from the nursery-web spider sparks polymerization as it experiences a drop in pH (Nature 2010, 465, 236). “The significance of the low pH at the spider’s gland outlet was not clear, and this surprising finding may well provide the answer,” says Uri Gat, a spider silk expert at Hebrew University of Jerusalem, in Israel.