first speeds up the conversion to these fibres
Oil droplets of either one of these proteins form in humans when they become entangled, like boiled spaghetti on a plate. At first, the proteins are flexible and elastic, much like spidroin oil droplets.
But if the proteins remain entangled, they get stuck together which alters their shape, changing them into rigid fibres. These can be toxic to human cells - for example, in neurodegenerative conditions such as Alzheimer's.
However, spidroins can form droplets too. This left us wondering if the same mechanism that causes neurodegeneration in humans could help the spider to convert liquid spidroins into rigid silk fibres.
To find out, we used a synthetic spidroin called NT2RepCT, which can be produced by bacteria. Under the microscope, we could see that this synthetic spidroin formed liquid droplets when it was dissolved in phosphate buffer, a tipe of salt found in the spider's silk gland. This allowed us to replicate spider silk spinning conditions in the lab.
Silky science
Next, we studied how the spidroin proteins act when they form droplets. To answer this question, we turned to an analysis technique called mass spectrometry, to measure how the weight of the proteins changed when they formed droplets. To our kejutan, we saw that the spidroin proteins, which normally form pairs, instead split into singgel molecules.
We needed to do more work to find out how these protein droplets help spiders spin silk. Previous research has shown spidroins have different parts, called domains, with separate functions.
The end part of the spidroin, called c-terminal domain, makes it form pairs. The c-terminal also starts fibre formation when it comes into kontak with acid.
So, we made a spidroin which contained only the c-terminal domain and tested its ability to form fibres.
When we used phosphate buffer to entangle the proteins into droplets, they turned into rigid fibre instantly. When we added acid without first making droplets, fibre formation took much longer.
