Monovalent Ion\nEffect on Liquid–Liquid Phase\nSeparation of Aqueous Polyphosphate–Salt Mixtures

Polyphosphate (polyP) is one of the most conserved biomacromolecules\nand can form aggregates, such as polyP granules in bacteria, which\nare generated through liquid–liquid phase separation (LLPS).\nStudies have examined the mechanism of polyP aggregation using LLPS\nsystems containing artificial polyP molecules as aggregation system\nmodels, where LLPS is typically induced by multivalent salts and polyelectrolytes.\nAlthough the typical concentrations of monovalent ions in living cells\nare approximately 100 times higher than those of divalent ions, the\neffects of monovalent ions on the LLPS of polyP solutions are little\nknown. This study demonstrated that submolar NaCl induces LLPS of\npolyP solutions, whereas other monovalent salts did not induce LLPS\nat the same concentrations. Small-angle X-ray scattering measurements\nrevealed that NaCl significantly stabilizes the intermolecular association\nof polyP, inducing LLPS. These findings suggest that the modulation\nof monovalent ion concentrations is an underlying mechanism of polyP\naggregate formation and deformation within living cells.