Studying protein polymerization with mass photometry

Protein polymerization underpins major biological processes, such as cell division and intracellular transport, while undesired assembly can lead to protein aggregates that are associated with, for example, neurodegenerative diseases and cancer.

The reaction steps that are linked to protein polymerization are traditionally studied by bulk-based methods and explained by kinetic modelling. Despite their widespread use, these techniques are often unable to account for the initial reaction steps; meanwhile, several contradictory models may fit the same dataset. With actin as an example, we sought to investigate established nucleation models for filament formation. We used mass photometry – a single-molecule bioanalytical technique – to quickly quantify all the species that are present in solution throughout the polymerization reaction and compare their distribution with model-based predictions.

Our results showed that the current models did not account for the distribution of actin oligomers observed from the mass photometry measurements. Combining a classical bulk approach with mass photometry led us to a new interpretation of the mechanism behind actin polymerization that took into account well-documented phenomena for actin, such as ATP hydrolysis and cation exchange, which had not been considered for nucleation before.

The same approach can be used for other protein polymers such as microtubules and amyloids, with applications in medicine and chemical industry.

 

Learning Objectives