Background 

High protein solubility is a key property for the development of protein-based products, such as chemical reagents and pharmacological medicines. A common method routinely applied in many laboratories is based on polyethylene glycol (PEG), a large molecule that induces protein precipitation. Even though this method has been used since the 1960s, it is still challenging, resource intensive, and low throughput. Marc Oeller was developing a software to predict protein solubility during his PhD in the Vendruscolo Lab, at the Yusuf Hamied Department of Chemistry, and he was planning to verify the predictions using the common PEG assay. “But what I found was that, first of all, the published methods were either very heavy on the material requirement or required very expensive pipetting robots. And even though they were published methods, I couldn’t find clear protocols,” says Marc. The Vendruscolo Lab decided to develop their own assay with a much cheaper robot, low material requirement, and with a medium to high throughput. The protocols are publicly available and open source, being a valuable resource for the scientific community.

Function

It is a fully automated PEG precipitation assay that uses a cost-effective open source pipetting robot, and low material consumption to assess relative solubility of proteins. 

Development process

Although the principle idea of the PEG precipitation protocol assay has been known for many years, Marc explained that working with PEG is challenging as it is an extremely viscous substance, like honey, making it almost impossible to accurately pipette small volumes (<5 µL) manually. The development process started with a very simple assay requiring high PEG volume, and then gradually scaled down to reduced volumes. The protocol optimisation was reasonably straightforward, but the tricky step was to tweak the robot to pipette the PEG volumes correctly. “We went down to less than a microlitre and that took a long time for us to get correct with the PEG,” says Marc. 

Target user

Researchers working on protein developability, protein drugs and protein solubility in general.

Comparison to other technologies

The main advantages of this protocol compared to others available are the low amount of material required, its higher throughput, and the lower cost. But the most valuable point is actually that it is open source, making it very easy to be implemented in other laboratories. “We set the whole thing up as being as open as possible, and that’s why we were happy with the robot that we used because the robot cost less than £10,000, which is still, of course, quite a jump, but several times cheaper than other robots,” explains Marc.