Event

Abstract: Phase separation compartmentalizes cells via the formation of membraneless organelles, also called biomolecular condensates. Phase separation influences many fundamental biological processes, from transcription to sorting of molecules and the stress response. Phase separation is mediated by a combination of associative and segregative phase transitions, or networking and a density transition, which together result in a percolated dense phase. Condensates therefore have emergent properties, i.e., properties that small complexes do not possess. These include material properties, which can be characterized in terms of dynamical moduli and can change as a function of the age of the condensate. While the lifetimes of small complexes are determined by the affinities of their constituent molecules, condensates cross the percolation line and therefore have long lifetimes. The mobility of individual biomolecules in the dense phase and between dilute and dense phases, are also determined by their interactions and can be high. Condensates have internal network structures and interfaces with the coexisting dilute phase, and the latter are characterized by distinct conformations of the biomolecules and can mediate specific biochemical functions. Not only biomolecules but also ions can partition asymmetrically between coexisting phases, and this depends on the ion concentration, salt type and the charge of the biomolecules that form the condensates. Asymmetric partitioning results in an electric potential between phases and across the interface. These membrane-like, interphase electric potentials predict that condensates can be responsive to changes in osmotic pressure and to changes in electrochemical potentials. Phase separation thus enables the formation of large assemblies with long lifetimes, high internal mobility, and biochemically active interfaces with electric potentials. I will discuss some of these recent insights and how they relate to condensate function and relationship to diseases.

Inquiries: nguyeny@sas.upenn.edu

Location: Carolyn Hoff Lynch Lecture Hall