Phase transition of RNA−protein complexes into ordered hollow condensates

Abstract

<jats:p>Liquid−liquid phase separation of multivalent intrinsically disordered protein−RNA complexes is ubiquitous in both natural and biomimetic systems. So far, isotropic liquid droplets are the most commonly observed topology of RNA−protein condensates in experiments and simulations. Here, by systematically studying the phase behavior of RNA−protein complexes across varied mixture compositions, we report a hollow vesicle-like condensate phase of nucleoprotein assemblies that is distinct from RNA−protein droplets. We show that these vesicular condensates are stable at specific mixture compositions and concentration regimes within the phase diagram and are formed through the phase separation of anisotropic protein−RNA complexes. Similar to membranes composed of amphiphilic lipids, these nucleoprotein−RNA vesicular membranes exhibit local ordering, size-dependent permeability, and selective encapsulation capacity without sacrificing their dynamic formation and dissolution in response to physicochemical stimuli. Our findings suggest that protein−RNA complexes can robustly create lipid-free vesicle-like enclosures by phase separation.</jats:p>

Sequence-encoded and Composition-dependent Protein-RNA Interactions Control Multiphasic Condensate Morphologies

“…1). The distinction between the core and surface compositions of RNA-RLD condensates can be attributed to differential solvation of non-stoichiometric RLD-RNA complexes at compositionally disproportionate mixtures 49 (Fig. 1d).…”

“…1d). For example, in RNA-rich condensates, an unbound or partiallycomplexed RNA chain is expected to have a larger effective solvation volume as compared to fully complexed RLD-bound RNA chains, resulting in free RNA chains being preferentially positioned on the condensate surface 49,62 (Fig. 1d-e).…”

“…1d). Such phase behavior is usually referred to as reentrant phase transition 28,47,49 . Within the reentrant phase separation window ( Fig.…”

“…1d), we previously predicted that disproportionate mixture compositions may lead to the formation of "micellar" condensates, in which the condensates' surfaces can be either enriched in RLDs or RNAs depending on the mixture stoichiometry 49 . To validate the micellar condensate formation in our system, we performed molecular dynamics (MD) simulations using a single-residue resolution coarse-grained model of an RLD from an archetypal ribonucleoprotein FUS (FUS RGG3 ) and a homopolymeric RNA, poly(U) 49 ( Table S2). The representative equilibrium structures of the RLD-RNA condensates revealed two distinct condensate architectures: (a) condensates with RLD-enriched surfaces at < , and (b) condensates with RNA-enriched surfaces at > (Fig.…”

“…S5). Therefore, these condensates appear to be spatially organized 49 and their surface composition is dynamically varied in an RNA dose-dependent manner.…”