Intracellular wetting mediates contacts between liquid compartments and membrane-bound organelles

Protein-rich droplets, such as stress granules, P-bodies, and the nucleolus, perform diverse and specialized cellular functions. Recent evidence has shown the droplets, which are also known as biomolecular condensates or membrane-less compartments, form by phase separation. Many droplets also contact membrane-bound organelles, thereby functioning in development, intracellular degradation, and organization. These underappreciated interactions have major implications for our fundamental understanding of cells. Starting with a brief introduction to wetting phenomena, we summarize recent progress in the emerging field of droplet–membrane contact. We describe the physical mechanism of droplet–membrane interactions, discuss how these interactions remodel droplets and membranes, and introduce "membrane scaffolding" by liquids as a novel reshaping mechanism, thereby demonstrating that droplet–membrane interactions are elastic wetting phenomena. “Membrane-less” and “membrane-bound” condensates likely represent distinct wetting states that together link phase separation with mechanosensitivity and explain key structures observed during embryogenesis, during autophagy, and at synapses. We therefore contend that droplet wetting on membranes provides a robust and intricate means of intracellular organization.

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Role of NADPH oxidase in the regulation of autophagy in cardiomyocytes

Clinical Science ◽

10.1042/cs20140336 ◽

2014 ◽

Vol 128 (7) ◽

pp. 387-403 ◽

Cited By ~ 20

Author(s):

Sebastiano Sciarretta ◽

Derek Yee ◽

Paul Ammann ◽

Narayani Nagarajan ◽

Massimo Volpe ◽

...

Keyword(s):

Nadph Oxidase ◽

Degradation Process ◽

Cellular Functions ◽

Signalling Molecules ◽

Intracellular Degradation ◽

The Past ◽

Cancer Cell Survival ◽

Membrane Bound ◽

Nox Family

In the past several years, it has been demonstrated that the reactive oxygen species (ROS) may act as intracellular signalling molecules to activate or inhibit specific signalling pathways and regulate physiological cellular functions. It is now well-established that ROS regulate autophagy, an intracellular degradation process. However, the signalling mechanisms through which ROS modulate autophagy in a regulated manner have only been minimally clarified. NADPH oxidase (Nox) enzymes are membrane-bound enzymatic complexes responsible for the dedicated generation of ROS. Different isoforms of Nox exist with different functions. Recent studies demonstrated that Nox-derived ROS can promote autophagy, with Nox2 and Nox4 representing the isoforms of Nox implicated thus far. Nox2- and Nox4-dependent autophagy plays an important role in the elimination of pathogens by phagocytes and in the regulation of vascular- and cancer-cell survival. Interestingly, we recently found that Nox is also important for autophagy regulation in cardiomyocytes. We found that Nox4, but not Nox2, promotes the activation of autophagy and survival in cardiomyocytes in response to nutrient deprivation and ischaemia through activation of the PERK (protein kinase RNA-like endoplasmic reticulum kinase) signalling pathway. In the present paper, we discuss the importance of Nox family proteins and ROS in the regulation of autophagy, with a particular focus on the role of Nox4 in the regulation of autophagy in the heart.

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Membrane-Bound Meet Membraneless in Health and Disease

Cells ◽

10.3390/cells8091000 ◽

2019 ◽

Vol 8 (9) ◽

pp. 1000 ◽

Cited By ~ 4

Author(s):

Chujun Zhang ◽

Catherine Rabouille

Keyword(s):

Phase Separation ◽

Membrane Trafficking ◽

Secretory Pathway ◽

Dependent Manner ◽

P Bodies ◽

Early Secretory Pathway ◽

Cell Organization ◽

Health And Disease ◽

Membrane Bound ◽

And Function

Membraneless organelles (MLOs) are defined as cellular structures that are not sealed by a lipidic membrane and are shown to form by phase separation. They exist in both the nucleus and the cytoplasm that is also heavily populated by numerous membrane-bound organelles. Even though the name membraneless suggests that MLOs are free of membrane, both membrane and factors regulating membrane trafficking steps are emerging as important components of MLO formation and function. As a result, we name them biocondensates. In this review, we examine the relationships between biocondensates and membrane. First, inhibition of membrane trafficking in the early secretory pathway leads to the formation of biocondensates (P-bodies and Sec bodies). In the same vein, stress granules have a complex relationship with the cyto-nuclear transport machinery. Second, membrane contributes to the regulated formation of phase separation in the cells and we will present examples including clustering at the plasma membrane and at the synapse. Finally, the whole cell appears to transit from an interphase phase-separated state to a mitotic diffuse state in a DYRK3 dependent manner. This firmly establishes a crosstalk between the two types of cell organization that will need to be further explored.

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Decoding the physical principles of two-component biomolecular phase separation

10.1101/2020.08.24.264655 ◽

2020 ◽

Author(s):

Yaojun Zhang ◽

Bin Xu ◽

Benjamin G. Weiner ◽

Yigal Meir ◽

Ned S. Wingreen

Keyword(s):

Phase Separation ◽

Coarse Grained ◽

Cellular Functions ◽

Ratio Effect ◽

Polymer Properties ◽

Binding Phase ◽

Membrane Bound ◽

Dynamics Simulations ◽

The Individual ◽

Physical Principles

Cells possess a multiplicity of non-membrane bound compartments, which form via liquid-liquid phase separation. These condensates assemble and dissolve as needed to enable central cellular functions. One important class of condensates is those composed of two associating polymer species that form one-to-one specific bonds. What are the physical principles that underlie phase separation in such systems? To address this question, we employed coarse-grained molecular dynamics simulations to examine how the phase boundaries depend on polymer valence, stoichiometry, and binding strength. We discovered a striking phenomenon – for sufficiently strong binding, phase separation is suppressed at rational polymer stoichiometries, which we termed the magic-ratio effect. We further developed an analytical dimer-gel theory that confirmed the magic-ratio effect and disentangled the individual roles of polymer properties in shaping the phase diagram. Our work provides new insights into the factors controlling the phase diagrams of biomolecular condensates, with implications for natural and synthetic systems.

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Decoding the physical principles of two-component biomolecular phase separation

eLife ◽

10.7554/elife.62403 ◽

2021 ◽

Vol 10 ◽

Author(s):

Yaojun Zhang ◽

Bin Xu ◽

Benjamin G Weiner ◽

Yigal Meir ◽

Ned S Wingreen

Keyword(s):

Phase Separation ◽

Coarse Grained ◽

Cellular Functions ◽

Ratio Effect ◽

Polymer Properties ◽

Binding Phase ◽

Membrane Bound ◽

Dynamics Simulations ◽

The Individual ◽

Physical Principles

Cells possess a multiplicity of non-membrane-bound compartments, which form via liquid-liquid phase separation. These condensates assemble and dissolve as needed to enable central cellular functions. One important class of condensates is those composed of two associating polymer species that form one-to-one specific bonds. What are the physical principles that underlie phase separation in such systems? To address this question, we employed coarse-grained molecular dynamics simulations to examine how the phase boundaries depend on polymer valence, stoichiometry, and binding strength. We discovered a striking phenomenon – for sufficiently strong binding, phase separation is suppressed at rational polymer stoichiometries, which we termed the magic-ratio effect. We further developed an analytical dimer-gel theory that confirmed the magic-ratio effect and disentangled the individual roles of polymer properties in shaping the phase diagram. Our work provides new insights into the factors controlling the phase diagrams of biomolecular condensates, with implications for natural and synthetic systems.

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The interplay of structural and cellular biophysics controls clustering of multivalent molecules

10.1101/373084 ◽

2018 ◽

Author(s):

A. Chattaraj ◽

M. Youngstrom ◽

L. M. Loew

Keyword(s):

Phase Separation ◽

Binding Sites ◽

Cluster Size ◽

Dependent Manner ◽

Size Distributions ◽

Cellular Functions ◽

Membrane Bound ◽

Nucleation Promoting Factor ◽

High Concentrations ◽

Liquid Liquid Phase Separation

AbstractDynamic molecular clusters are assembled through weak multivalent interactions and are platforms for cellular functions, especially receptor-mediated signaling. Clustering is also a prerequisite for liquid-liquid phase separation. But it is not well understood how molecular structure and cellular organization control clustering. Using coarse-grain kinetic Langevin dynamics, we performed computational experiments on a prototypical ternary system modeled after membrane-bound nephrin, the adaptor Nck1 and the actin nucleation promoting factor NWASP. Steady state cluster size distributions favored stoichiometries that optimized binding (stoichiometry matching), but still were quite broad. At high concentrations, the system can be driven beyond the saturation boundary such that cluster size is limited only by the number of available molecules. This behavior would be predictive of phase separation. Domains close to binding sites sterically inhibited clustering much less than terminal domains because the latter effectively restrict access to the cluster interior. Increased flexibility of interacting molecules diminished clustering by shielding binding sites within compact conformations. Membrane association of nephrin increased the cluster size distribution in a density-dependent manner. These properties provide insights into how molecular ensembles function to localize and amplify cell signaling.

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Microscopic investigations of novel intracellular bodies of a Nocardia SP

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100169511 ◽

1994 ◽

Vol 52 ◽

pp. 356-357

Author(s):

J. L. Stites

Keyword(s):

Uranyl Acetate ◽

Electron Microscopic ◽

En Bloc ◽

Ribonucleic Acids ◽

Transmission Electron ◽

Nocardia Sp ◽

Internal Constitution ◽

Membrane Bound ◽

Molecular Components ◽

Protein Rich

A Nocardia sp.was found during an initial transmission electron microscopic (TEM) examination to have unusual intracellular bodies (ICB's) which do not appear to have been described previously in the literature. Most intracellular structures within bacteria have been classified as storage granules, a product of membrane invagination (i.e. mesosomes), or vacuoles. In bacteria there are no known intracellular membrane-bound organelles, and all internal membranes are invaginations of the unit membrane. Several microscopic-level examinations of the Nocardia sp. ICB's were initiated in order to determine their overall structure, classification, and internal constitution.Different TEM staining procedures were performed to determine possible molecular components of the ICB. In all of the staining protocols the ICB's showed a lack of electron density similar to the cell wall. Because the ICB's showed no affinity to any stain, it appeared they do not have strong positive charge (phosphotungstic acid), are not protein rich (en bloc uranyl acetate), lack glycogen and are not phosphate or sulphur rich (lead citrate), nor do they contain lipids or ribonucleic acids (osmium tetroxide).

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Focusing on mRNA Granules and Stalled Polysomes Amidst Diverse Mechanisms Underlying mRNA Transport, mRNA Storage, and Local Translation

The Oxford Handbook of Neuronal Protein Synthesis ◽

10.1093/oxfordhb/9780190686307.013.20 ◽

2020 ◽

Author(s):

Mina N. Anadolu ◽

Wayne S. Sossin

Keyword(s):

Protein Synthesis ◽

Liquid Phase ◽

Mrna Translation ◽

Rna Transport ◽

P Bodies ◽

Rna Granules ◽

Mrna Granules ◽

Transport Particle ◽

As Stress ◽

The Individual

In neurons, mRNAs are transported to distal sites to allow for localized protein synthesis. There are many diverse mechanisms underlying this transport. For example, an individual mRNA can be transported in an RNA transport particle that is tailored to the individual mRNA and its associated binding proteins. In contrast, some mRNAs are transported in liquid-liquid phase separated structures called neuronal RNA granules that are made up of multiple stalled polysomes, allowing for rapid initiation-independent production of proteins required for synaptic plasticity. Moreover, neurons have additional types of liquid-liquid phase–separated structures containing mRNA, such as stress granules and P bodies. This chapter discusses the relationships between all of these structures, what proteins distinguish them, and the possible roles they play in the complex control of mRNA translation at distal sites that allow neurons to use protein synthesis to refine their local proteome in many different ways.

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In situ microscopic studies on the structures and phase behaviors of SF/PEG films using solid-state NMR and Raman imaging

Physical Chemistry Chemical Physics ◽

10.1039/c6cp03314h ◽

2016 ◽

Vol 18 (24) ◽

pp. 16353-16360 ◽

Cited By ~ 7

Author(s):

Congheng Chen ◽

Ting Yao ◽

Sidong Tu ◽

Weijie Xu ◽

Yi Han ◽

...

Keyword(s):

Phase Separation ◽

Solid State Nmr ◽

Random Coil ◽

Rich Domain ◽

Microscopic Studies ◽

Helix Conformation ◽

Phase Behaviors ◽

Protein Rich ◽

Β Sheet

SF was incompatible with PEG in some extent, and the phase separation took place in their blend film. The conformation of SF in the interface between SF and PEG was changed to the β-sheet, while that in the protein-rich domain remained in the random coil and/or helix conformation.

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