Reentrant DNA shells tune polyphosphate condensate size

Abstract

The ancient, inorganic biopolymer polyphosphate (polyP) occurs in all three domains of life and affects myriad cellular processes. An intriguing feature of polyP is its frequent proximity to chromatin, and in the case of many bacteria, its occurrence in the form of magnesium-enriched condensates embedded in the nucleoid, particularly in response to stress. The physical basis of the interaction between polyP and DNA, two fundamental anionic biopolymers, and the resulting effects on the organization of both the nucleoid and polyP condensates remain poorly understood. Given the essential role of magnesium ions in the coordination of polymeric phosphate species, we hypothesized that a minimal system of polyP, magnesium ions, and DNA (polyP-Mg2+-DNA) would capture key features of the interplay between the condensates and bacterial chromatin. We find that DNA can profoundly affect polyP-Mg2+coacervation even at concentrations several orders of magnitude lower than found in the cell. The DNA forms shells around polyP-Mg2+condensates and these shells show reentrant behavior, primarily forming in the concentration range close to polyP-Mg2+charge neutralization. This surface association tunes both condensate size and DNA morphology in a manner dependent on DNA properties, including length and concentration. Our work identifies three components that could form the basis of a central and tunable interaction hub that interfaces with cellular interactors. These studies will inform future efforts to understand the basis of polyP granule composition and consolidation, as well as the potential capacity of these mesoscale assemblies to remodel chromatin in response to diverse stressors at different length and time scales.

A mammalian model reveals inorganic polyphosphate channeling into the nucleolus and induction of a hyper-condensate state

“…Secondly, recent literature indicates that polyP induces LLPS of positively charged proteins 36 and can contribute to the formation of phase-separated condensates in bacterial chromatin structure. 63 , 64 Conventional LLPS is typically driven by the charged nature of nucleic acids and their association with DNA- or RNA-specific binding proteins. Highly charged polyP might use its ability to interact with positively charged protein domains 36 or coordinate cations and induce LLPS.…”

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

“…This result can be attributed to the loss of charge balance caused by the excess amount of cation. 28 This study mainly focused on the effect of monovalent ions on LLPS of the polyP solution. However, not only submolar monovalent ions but also millimolar divalent ions coexist in living cells.…”