How Spiders Efficiently Spin Smooth Silk for Their Webs

Spider silk is lightweight, strong and stretchy, making it one of the most amazing natural materials in the world. Now, scientists have taken a closer look at spider silk and have found out exactly how spiders manage to manufacture it so quickly.

Spider silk is created with silk proteins, called spidroins. Spiders need to convert these spidroins from a soluble form to solid fibers at ambient temperatures with water as a solvent. Spidroins themselves are large proteins, made up of about 3,500 amino acids that contain mostly repetitive sequences. The most important parts for converting spidroins into silk, though, are the ends.

The ends of the large spidroin proteins are unique to spider silk and are very similar between different spiders. Spidroins have a helical and unordered structure when stored as soluble proteins in silk glands. However, when converted to silk, they change completely to one that has a high degree of mechanical stability. This is triggered by a pH gradient present between one end of the spider silk gland to the other.

In order to learn a bit more about this process, the researchers used highly selective microelectrodes to measure the pH within the glands. They found that it falls from a neutral pH of 7.6 to an acidic pH of 5.7 between the beginning of the tail and halfway down the duct. This revealed that the pH gradient was far steeper than previously thought.

That's not all the researchers found, either. The pH had opposite effects on the stability of the two regions at each end of the spidroin proteins. This revealed that both ends of the protein undergo dramatic structural changes at the pH found at the beginning of the duct.

The findings reveal a bit more about spider silk formation, and show how spiders manage to spin it so quickly. These insights aren't just important for learning more about the natural world, though; because spider silk is such a useful material, it could be used in materials science in the future.

The findings are published in the journal PLOS Biology.