The manuscript examines the aggregation propensity of the FUS ALS-associated mutation, P525L. The authors use bioinformatic tools to show that the P525L mutation causes a decrease in solubility and increase in aggregation propensity. The purified P525L FUS protein formed aggregates in vitro as shown by turbidity measurements. Furthermore, phase separation of the WT FUS protein could be induced, and this phase behaviour is concentration-dependent.
The findings address possible explanations of how disease-specific mutation might cause the disease in the rapidly emerging area of phase separation. Overall this is a well-written paper with clear aims. The experiments were well-executed and the findings will be of interest to a broad readership.
The significance or impact of the findings should be emphasised more in the introduction and/or discussion: how does our understanding of the P525L aggregation behaviour impact future work? Whether this could be utilized for disease modelling in cells or identifying therapeutic targets, etc. As the authors mention, they did not analyse the phase behaviour of P525L (only the WT FUS) due to difficulties with purification. This is unfortunate as this would have provided more impact to the study. Phase separation of FUS protein itself isn’t new, but the novel observation in this paper is that purified P525L has a high propensity to aggregate and so will still be of interest to people in the field.