Abnormal Suppression of LLPS of Protein in Mild Salt Con-centrations

Abstract

Liquid-liquid phase separation (LLPS) is a significant biological phenomenon that plays a crucial role in biomaterials science and protein crystallization.In this study, we explored the phase behavior of proteins in various metal cationic solutions containing polyethylene glycol.As expected, we observed that low salt concentrations promoted LLPS, consistent with previous studies.However, LLPS was suppressed as salt concentrations increased further.Specifically, the critical protein concentration required for LLPS rose with higher salt concentrations.We found that the promotion and suppression of LLPS are influenced by the valence of the ions.Notably, divalent cationic salts exhibited a more pronounced promotional effect on protein phase separation at low salt concentrations than monovalent cationic salts.In contrast, at higher salt concentrations, monovalent cationic salts had a stronger inhibitory effect on LLPS compared to divalent cationic salts.This can be attributed to the ionic shielding effect at low salt concentrations and the formation of a hydration layer at higher salt concentrations, which increases short-range repulsive interactions between protein molecules.Interestingly, the suppressive effect was absent in trivalent cationic solutions.