Liquid–liquid phase separation of tau protein: The crucial role of electrostatic interactions

Abstract

Recent studies have indicated that tau, a protein involved in Alzheimer's disease and other neurodegenerative disorders, has a propensity to undergo liquid–liquid phase separation (LLPS). However, the mechanism of this process remains unknown. Here, we demonstrate that tau LLPS is largely driven by intermolecular electrostatic interactions between the negatively charged N-terminal and positively charged middle/C-terminal regions, whereas hydrophobic interactions play a surprisingly small role. Furthermore, our results reveal that, in contrast to previous suggestions, phosphorylation is not required for tau LLPS. These findings provide a foundation for understanding the mechanism by which phosphorylation and other posttranslational modifications could modulate tau LLPS in the context of specific physiological functions as well as pathological interactions.

Zinc promotes liquid–liquid phase separation of tau protein

“…Consistent with previously published data (15), in the absence of any crowding agents, freshly prepared solution of tau441 (10 µM) at neutral pH in 10 mM HEPES buffer (pH 7.4) containing 10-150 mM NaCl shows no measurable turbidity, indicating that the protein exists in a single phase, most likely as a monomer (21). However, upon addition of Zn 2+ (40 µM) to the protein solution at low ionic strength (10 mM HEPES, 10 mM NaCl, pH 7.4), a large increase in turbidity was observed ( Fig.…”

“…The previous study (15) (performed using similar experimental conditions but a more potent crowding agent, PEG 10) revealed that, in the absence of zinc, the N-terminally truncated tau441 variants Δ1-243 and Δ1-117 as well as the K18 fragment lost the ability to undergo LLPS, whereas the propensity of the Δ2N and Δ4R variants for LLPS was diminished (but not completely abrogated), as indicated by the requirement for higher concentrations of the crowding agent compared with that for tau441. This, together with data shown herein in Fig.…”

“…Recent reports indicate that, under certain conditions, full-length tau can undergo liquidliquid phase separation (LLPS), whereby the protein condenses into liquid droplets (13)(14)(15). This can occur upon the addition of RNA (13) or, for protein alone, in the presence of crowding agents that mimic high concentration of macromolecules in the intracellular environment (14-16).…”

“…This can occur upon the addition of RNA (13) or, for protein alone, in the presence of crowding agents that mimic high concentration of macromolecules in the intracellular environment (14-16). Even though it was originally suggested that only phosphorylated tau can undergo LLPS in the absence of polyanions such as RNA (14), more recent studies revealed that this process does not require phosphorylation (or any other posttranslational modifications), and that tau LLPS is driven by attractive electrostatic intermolecular interactions between oppositely charged domains of the protein (15). Furthermore, limited observations indicate that tau LLPS may also occur in neurons (14).…”

Granulins modulate liquid-liquid phase separation and aggregation of TDP-43 C-terminal domain

“…The findings of this study showcase how GRNs -3 and -5 modulate the dynamics of TDP-43CTD in forming insoluble aggregates or SGs in both oxidizing and reducing conditions. It is clear from the data that GRN-3 and GRN-5 affect TDP-43CTD aggregation via disparate mechanisms; while GRN-3 induces the formation of insoluble inclusions, GRN-5 coacervates with TDP-43CTD to undergo LLPS in both reduced and oxidized forms an interaction which is likely to be driven by the counter-ionic electrostatic characteristics of TDP-43CTD and the negatively charged GRN-5 which are known to be common mediators of LLPS (85)(86)(87). Furthermore, GRN-3 and GRN-5 also disrupt SGs formed by RNA and TDP-43CTD.…”