Molecular Crowding Tunes Material States of Ribonucleoprotein Condensates.

Taranpreet Kaur,Priya Banerjee,Mahdi Moosa,Jason Ngo,Wei Wang,Ibraheem Alshareedah

doi:10.3390/biom9020071

Taranpreet Kaur, Priya Banerjee + Show 4 more

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https://doi.org/10.3390/biom9020071

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Abstract

Ribonucleoprotein (RNP) granules are membraneless liquid condensates that dynamically form, dissolve, and mature into a gel-like state in response to a changing cellular environment. RNP condensation is largely governed by promiscuous attractive inter-chain interactions mediated by low-complexity domains (LCDs). Using an archetypal disordered RNP, fused in sarcoma (FUS), here we study how molecular crowding impacts the RNP liquid condensation. We observe that the liquid–liquid coexistence boundary of FUS is lowered by polymer crowders, consistent with an excluded volume model. With increasing bulk crowder concentration, the RNP partition increases and the diffusion rate decreases in the condensed phase. Furthermore, we show that RNP condensates undergo substantial hardening wherein protein-dense droplets transition from viscous fluid to viscoelastic gel-like states in a crowder concentration-dependent manner. Utilizing two distinct LCDs that broadly represent commonly occurring sequence motifs driving RNP phase transitions, we reveal that the impact of crowding is largely independent of LCD charge and sequence patterns. These results are consistent with a thermodynamic model of crowder-mediated depletion interaction, which suggests that inter-RNP attraction is enhanced by molecular crowding. The depletion force is likely to play a key role in tuning the physical properties of RNP condensates within the crowded cellular space.

Highlights

Ribonucleoprotein (RNP) granules or particles are a diverse group of subcellular compartments that are utilized by eukaryotic cells to spatiotemporally organize various biomolecular processes.These non-membranous assemblies, termed as membraneless organelles (MLOs), dynamically form, dissolve, and tune their physicochemical microenvironment in response to changing cellular cues [1,2,3]
Utilizing an archetypal RNP, fused in sarcoma (FUS), as well as representatives of the two commonly occurring low-complexity domains (LCDs) sequences in eukaryotic RNPs, we demonstrate an important role of crowding in modulating the mesoscale fluid dynamics of RNP condensates
Aberrant alterations the droplet states, such ageasonset loss of lossfluidity of granule and formation of assemblies, solid-like assemblies, are implicated inneurological various neurological granule andfluidity formation of solid-like are implicated in various disorders, disorders, ALS and frontotemporal dementia (FTD)Over

Summary

Introduction

Ribonucleoprotein (RNP) granules or particles are a diverse group of subcellular compartments that are utilized by eukaryotic cells to spatiotemporally organize various biomolecular processes. These non-membranous assemblies, termed as membraneless organelles (MLOs), dynamically form, dissolve, and tune their physicochemical microenvironment in response to changing cellular cues [1,2,3]. RNP granules are enriched in proteins with low-complexity domains (LCDs) that are structurally disordered [4,5,6], and are assumed to be formed by RNP liquid–liquid phase separation (LLPS) [7]. LCD-mediated promiscuous interactions can act synergistically with sequence-specific interactions in many RNPs, thereby shaping their global

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