Nobeyama, T. | bioRxiv Science

bioRxiv2024

Monovalent Ion Effect on Liquid-Liquid Phase Separation of Aqueous Polyphosphate-Salt Mixtures

Polyphosphate (polyP) is one of the most conserved biomacromolecules and can form aggregates, such as polyP granules in bacteria, which are generated through liquid-liquid phase separation (LLPS). Studies have examined the mechanism of polyP aggregation using LLPS systems containing artificial polyP molecules as aggregation system models, where LLPS is typically induced by multivalent salts and polyelectrolytes. Although the typical concentrations of monovalent ions in living cells are approximately 100 times higher than those of divalent ions, the effects of monovalent ions on the LLPS of polyP solutions are little known. This study demonstrated that submolar NaCl induces LLPS of polyP solutions, whereas other monovalent salts did not at the same concentrations. Small-angle X-ray scattering measurements revealed that NaCl significantly stabilizes the intermolecular association of polyP, inducing LLPS. These findings suggest that the modulation of monovalent ion concentrations is an underlying mechanism of polyP aggregate formation/deformation within living cells. TOC GRAPHIC O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=163 SRC="FIGDIR/small/592046v1_ufig1.gif" ALT="Figure 1"> View larger version (41K): org.highwire.dtl.DTLVardef@11bc9f4org.highwire.dtl.DTLVardef@167ee3corg.highwire.dtl.DTLVardef@49e055org.highwire.dtl.DTLVardef@27032a_HPS_FORMAT_FIGEXP M_FIG C_FIG

biophysics↗

bioRxiv2023

Reentrant condensation of a multicomponent complex system of biomolecules induced by polyphosphate

Reentrant condensation (RC) is a phase behavior of protein solution comprising at least two components. In RC, a protein state varies from one phase to two phases and then back to one phase as the concentration of one component monotonically increases. To understand the phase behavior of multicomponent complex solutions of biomolecules, it is worth constructing an experimental multicomponent system that exhibits RC behavior. Here, we used a cola/milk mixture to investigate RC of a multicomponent complex system and explained the RC mechanism by reducing the system to two pure components, polyphosphate (polyP) and casein. In the multicomponent complex system, RC was observed with 20-60% cola and 1% milk. In the pure system, RC occurred with 0.01-2 mM tetraphosphate and 0.5 mg/ml casein. Moreover, the phase diagram showed that the condensation of casein depended on the chain length of the polyP. The present study succeeded in experimentally inducing RC in a multicomponent system and reproducing RC even when the system was reduced to its pure components. The fact that RC can be experimentally induced using common materials will provide important insights into the understanding of phase-separation behavior of biomolecules.

biochemistry↗