Abstract

Recent years have seen a significant change in the way we view the intracellular environment. We now recognise the ubiquitous presence of droplets or condensates composed of RNA and/or proteins that form through a phase separation like process. In this talk, I will discuss several problems related to these condensates. First, motivated by the fine compositional control observed in membraneless droplet organelles in cells, we investigate how a sharp binding-unbinding transition can occur between multivalent client molecules and receptors embedded in a porous three-dimensional structure. In contrast to similar superselective binding previously observed at surfaces, we have identified that a key effect in a three-dimensional environment is that the presence of inert crowding agents can significantly enhance or even introduce superselectivity [1]. Second, during seed development of the plant Arabidopsis thaliana, micrometer-sized liquid droplets form within the vacuolar lumen and wet the tonoplast. Distinct tonoplast shapes arise in response to membrane wetting by droplets and I will discuss a simple theoretical model that conceptualises and rationalises these geometries [2]. Conditions of low membrane spontaneous curvature and moderate wettability favor droplet-induced membrane budding, whereas high membrane spontaneous curvature and strong wettability promote a membrane nanotube network that forms exclusively at the droplet surface. Finally, if there is time, I will discuss an approach based on flicker spectroscopy to measure the surface tension of condensates in live cells and apply it to stress granules induced by different chemicals [3].

References: [1]. A. R. Christy, H. Kusumaatmaja and M. A. Miller, PRL 126 , 028002 (2021); [2] H. Kusumaatmaja et al., PNAS 118 , e2024109118 (2021); [3] J. O. Law, C. M. Jones, H. Kusumaatmaja and S. N. Grellscheid, in preparation (2022).