Chemistry of active coacervate droplets: Liquid droplets as a minimal model of life

Radboud University, 11 oktober 2021
Promotor : Huck, W.T.S. Co-promotor : Spruijt, E.
Contains fulltext : 237467.pdf (Publisher’s version ) (Open Access)
The chemical principles behind many vital processes are an open question in science. Be it to understand how cells emerged from inanimate matter, or to be able to create close mimics of cells and organisms, simple chemistry can go a long way. In this thesis we take one chemical system in particular, coacervates, and explore its capabilities as protocells. Coacervate droplets are a dense liquid phase that originates from the liquid-liquid phase separation of a polyelectrolyte mixture. The droplets are generally rich in macromolecules, such as proteins, and can be compared to membraneless organelles in modern cells, points on which we expand in Chapter 1. In Chapter 2 we develop a minimal enzymatic network to control the assembly and disassembly of droplets; we achieve this by working with ATP-based coacervates and a kinase/phosphatase pair. In Chapter 3 we discuss how the presence of droplets can affect biochemical reactions, and in Chapter 4 we develop a kinetic model to demonstrate the effect. We find that droplets can increase overall reaction rates by increasing local concentrations, or by segregating a substrate from an inhibitor for example. In Chapter 5 we move towards monitoring coacervate droplets over time, and find that complex coacervates, unlike other liquids, do not undergo Ostwald ripening in the time range of our interest. Finally, in Chapter 6 we gather the previous results to achieve growing droplets, completely controlled by a kinase reaction and protein diffusion. In Chapters 7 and 8 we integrate our findings and propose an outlook to our research. Together, our results shed light on chemistry in compartments like droplets and membraneless organelles, and also on mechanisms by which primitive cells could have grown and proliferated.