Biological Condensate Growth: Examining the Impact of Solute Crowder on Size Expansion

Biological condensation refers to the formation of micrometer-sized or smaller condensates by biological macromolecules, a process often influenced by the crowded cellular environment. Poly(ethylene glycol) (PEG) is commonly used to mimic cellular crowding, and its ability to reduce the critical nucleation concentration has been well established. However, its impact on condensate size has been less explored. This study investigates how PEG affects the size of condensates formed between protein TNP1 and DNA. Our experimental findings show that PEG molecules increase condensate size. Notably, at equal mass concentrations of PEG400, PEG3350, and PEG10000, longer PEG molecules have a much greater effect on condensate expansion. Computational simulations further reveal that longer PEG molecules enhance protein-DNA condensation more effectively and contribute to shaping the condensates into regular forms. Overall, our study provides key insights into how crowding factors influence the size and shape of colloidal growth.