The aim of this project was to better understand the shapes and behaviour of a protein called UBQLN-2. This is a protein involved in Amyotrophic Lateral Sclerosis (ALS), which is the disease that you might remember from the ice bucket challenge, the purpose of which was to raise awareness of ALS. ALS is also known as motor neurone disease or Lou Gehrig’s Disease, after a famous baseball player who died from the disease. Theoretical Physicist Stephen Hawking also had ALS.
UBQLN2 is an intrinsically disordered protein, which means that it has a very flexible shape and is therefore very difficult to study. It also behaves differently according to the solution which it’s in. If it’s in a low-salt solution, UBQLN2 dissolves evenly in the solution. However in a high-salt solution, UBQLN2 forms droplets in a similar way to oil forming droplets in water. The way in which UBQLN2 forms droplets is a process called liquid liquid phase separation, and it’s an important process in normal cells as well as disease states.
By studying UBQLN2 at low salt and high salt solutions, we found out that at high salt concentrations it has a more extended shape, whereas at low salt solutions it exists in a wide range of shapes, ranging from compact to extended. Moreover when we add another protein called ubiquitin, which prevents the formation of protein droplets, UBQLN2 is pushed to a much more compact shape. We therefore identified that UBQLN2 is more extended in solutions that favour the formation of droplets, and more compact in solutions that prevent the droplets from occurring.
The scientific method that we use in the group, and that we used to study UBQLN2, is called native ion mobility mass spectrometry. It is ideally suited to intrinsically disordered proteins as it separates proteins on the basis of their overall size. It’s a relatively new way of measuring proteins, and this work demonstrates its strengths as this detailed information about the size changes of the full UBQLN2 protein is challenging to gain with other methods. This is due to the complexity of the protein shapes, with such a wide variety.
This work was led by Christina Robb who is a PhD student under the supervision of Rebecca Beveridge. It is part of an ongoing collaboration with the Castañeda Lab at Syracuse University in New York State, and with Jakub Ujma from Waters Corp who sponsors Christina’s PhD.
You can read the published article here.