scholarly journals Beyond Langmuir: surface-bound macromolecule condensates

2020 ◽  
Vol 31 (23) ◽  
pp. 2502-2508
Author(s):  
T. J. Mitchison
Keyword(s):  
Phase Separation ◽  
Lipid Bilayers ◽  
Cell Biology ◽  
Test Case ◽  
Surface Binding ◽  
Multilayer Adsorption ◽  
Low Concentrations ◽  
Binding Surface ◽  
Bet Theory ◽  
Physical Biochemistry

Macromolecule condensates, phase separation, and membraneless compartments have become an important area of cell biology research where new biophysical concepts are emerging. This article discusses the possibility that condensates assemble on multivalent surfaces such as DNA, microtubules, or lipid bilayers by multilayer adsorption. Langmuir isotherm theory conceptualized saturable surface binding and deeply influenced physical biochemistry. Brunauer-Emmett-Teller (BET) theory extended Langmuir’s ideas to multilayer adsorption. A BET-inspired biochemical model predicts that surface-binding proteins with a tendency to self-associate will form multilayered condensates on binding surfaces. These “bound condensates” are expected to assemble well below the saturation concentration for liquid–liquid phase separation, so they can compete subunits away from phase-separated droplets and are thermodynamically pinned to the binding surface. Tau binding to microtubules is an interesting test case. The nonsaturable binding isotherm is reminiscent of BET predictions, but assembly of Tau-rich domains at low concentrations requires a different model. Surface-bound condensates may find multiple biological uses, particularly in situations where it is important that condensate assembly is spatially constrained, such as gene regulation.

scholarly journals Membrane-associated phase separation: organization and function emerge from a two-dimensional milieu

2021 ◽  
Author(s):  
Jonathon A Ditlev
Keyword(s):  
Phase Separation ◽  
Cell Biology ◽  
Cellular Environment ◽  
Condensate Formation ◽  
Associated Proteins ◽  
Available Technology ◽  
And Function ◽  
Surrounding Membrane

Abstract Liquid‒liquid phase separation (LLPS) of biomolecules has emerged as an important mechanism that contributes to cellular organization. Phase separated biomolecular condensates, or membrane-less organelles, are compartments composed of specific biomolecules without a surrounding membrane in the nucleus and cytoplasm. LLPS also occurs at membranes, where both lipids and membrane-associated proteins can de-mix to form phase separated compartments. Investigation of these membrane-associated condensates using in vitro biochemical reconstitution and cell biology has provided key insights into the role of phase separation in membrane domain formation and function. However, these studies have generally been limited by available technology to study LLPS on model membranes and the complex cellular environment that regulates condensate formation, composition, and function. Here, I briefly review our current understanding of membrane-associated condensates, establish why LLPS can be advantageous for certain membrane-associated condensates, and offer a perspective for how these condensates may be studied in the future.

scholarly journals Comparison of the Influence of 45S5 and Cu-Containing 45S5 Bioactive Glass (BG) on the Biological Properties of Novel Polyhydroxyalkanoate (PHA)/BG Composites

Materials ◽  
2020 ◽  
Vol 13 (11) ◽  
pp. 2607 ◽  
Author(s):  
Katharina Schuhladen ◽  
Barbara Lukasiewicz ◽  
Pooja Basnett ◽  
Ipsita Roy ◽  
Aldo R. Boccaccini
Keyword(s):  
Tissue Engineering ◽  
Cell Biology ◽  
Inorganic Compounds ◽  
Release Kinetics ◽  
Biological Properties ◽  
Long Term Effects ◽  
Salt Leaching ◽  
Low Concentrations ◽  
A Minor ◽  
Hard Tissue Engineering

Polyhydroxyalkanoates (PHAs), due to their biodegradable and biocompatible nature and their ability to be formed in complex structures, are excellent candidates for fabricating scaffolds used in tissue engineering. By introducing inorganic compounds, such as bioactive glasses (BGs), the bioactive properties of PHAs can be further improved. In addition to their outstanding bioactivity, BGs can be additionally doped with biological ions, which in turn extend the functionality of the BG-PHA composite. Here, different PHAs were combined with 45S5 BG, which was additionally doped with copper in order to introduce antibacterial and angiogenic properties. The resulting composite was used to produce scaffolds by the salt leaching technique. By performing indirect cell biology tests using stromal cells, a dose-depending effect of the dissolution products released from the BG-PHA scaffolds could be found. In low concentrations, no toxic effect was found. Moreover, in higher concentrations, a minor reduction of cell viability combined with a major increase in VEGF release was measured. This result indicates that the fabricated composite scaffolds are suitable candidates for applications in soft and hard tissue engineering. However, more in-depth studies are necessary to fully understand the release kinetics and the resulting long-term effects of the BG-PHA composites.

Biological Phase Separation and Biomolecular Condensates in Plants

2021 ◽  
Vol 72 (1) ◽  
Author(s):  
Ryan J. Emenecker ◽  
Alex S. Holehouse ◽  
Lucia C. Strader
Keyword(s):  
Phase Separation ◽  
Cell Biology ◽  
Condensed Matter ◽  
Annual Review ◽  
Publication Date ◽  
Nuclear Speckles ◽  
The Past ◽  
Shared Property ◽  
And Function ◽  
Physical Principles

A surge in research focused on understanding the physical principles governing the formation, properties, and function of membraneless compartments has occurred over the past decade. Compartments such as the nucleolus, stress granules, and nuclear speckles have been designated as biomolecular condensates to describe their shared property of spatially concentrating biomolecules. Although this research has historically been carried out in animal and fungal systems, recent work has begun to explore whether these same principles are relevant in plants. Effectively understanding and studying biomolecular condensates require interdisciplinary expertise that spans cell biology, biochemistry, and condensed matter physics and biophysics. As such, some involved concepts may be unfamiliar to any given individual. This review focuses on introducing concepts essential to the study of biomolecular condensates and phase separation for biologists seeking to carry out research in this area and further examines aspects of biomolecular condensates that are relevant to plant systems. Expected final online publication date for the Annual Review of Plant Biology, Volume 72 is May 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

scholarly journals Non-axisymmetric shapes of biological membranes from locally induced curvature

2019 ◽  
Author(s):  
Yannick A. D. Omar ◽  
Amaresh Sahu ◽  
Roger A. Sauer ◽  
Kranthi K. Mandadapu
Keyword(s):  
Phase Separation ◽  
Cell Membrane ◽  
Viscous Flow ◽  
Lipid Bilayers ◽  
Biological Membranes ◽  
Rate Of Change ◽  
Computational Studies ◽  
Biological Processes ◽  
Resting Tension ◽  
Physical Phenomena

In various biological processes such as endocytosis and caveolae formation, the cell membrane is locally deformed into curved configurations. Previous theoretical and computational studies to understand membrane morphologies resulting from locally induced curvature are often limited to axisymmetric shapes, which severely restricts the physically admissible morphologies. Under the restriction of axisymmetry, past efforts predict that the cell membrane buds at low resting tensions and stalls at a flat pit at high resting tensions. In this work, we lift the restriction of axisymmetry by employing recent theoretical and numerical advances to understand arbitrarily curved and deforming lipid bilayers. Our non-axisymmetric morphologies reveal membrane morphologies which agree well with axisymmetric studies—however only if the resting tension of the membrane is low. When the resting tension is moderate to high, we show that (i) axisymmetric invaginations are unstable; and (ii) non-axisymmetric ridge-shaped structures are energetically favorable. We further study the dynamical effects resulting from the interplay between intramembrane viscous flow and induced curvature, and find the rate at which the locally induced curvature increases is a key determinant in the formation of ridges. In particular, we show that axisymmetric buds are favored when the induced curvature is rapidly increased, while non-axisymmetric ridges are favored when the curvature is slowly increased: The rate of change of induced curvature affects the intramembrane viscous flow of lipids, which can impede the membrane’s ability to transition into ridges. We conclude that the appearance of non-axisymmetric ridges indicates that axisymmetry cannot be generally assumed when understanding processes involving locally induced curvature. Our results hold potentially relevant implications for biological processes such as endocytosis, and physical phenomena like phase separation in lipid bilayers.

scholarly journals Curvature-driven feedback on aggregation-diffusion of proteins in lipid bilayers

Soft Matter ◽  
2021 ◽  
Author(s):  
Arijit Mahapatra ◽  
David Saintillan ◽  
Padmini Rangamani
Keyword(s):  
Lipid Bilayers ◽  
Cell Biology ◽  
Membrane Bending ◽  
Curvature Driven

Membrane bending is an extensively studied problem from both modeling and experimental perspectives because of the wide implications of curvature generation in cell biology. Many of the curvature generating aspects...

scholarly journals A Novel Lens for Cell Volume Regulation: Liquid-Liquid Phase Separation

2021 ◽  
Vol 55 (S1) ◽  
pp. 135-160
Keyword(s):  
Phase Separation ◽  
Cell Membrane ◽  
Cell Volume ◽  
Volume Change ◽  
Cell Biology ◽  
Cell Volume Regulation ◽  
Organic Osmolytes ◽  
Regulatory Systems ◽  
Osmotic Water ◽  
Intracellular Changes

Cells are constantly exposed to the risk of volume perturbation under physiological conditions. The increase or decrease in cell volume accompanies intracellular changes in cell membrane tension, ionic strength/concentration and macromolecular crowding. To avoid deleterious consequences caused by cell volume perturbation, cells have volume recovery systems that regulate osmotic water flow by transporting ions and organic osmolytes across the cell membrane. Thus far, a number of biomolecules have been reported to regulate cell volume. However, the question of how cells sense volume change and modulate volume regulatory systems is not fully understood. Recently, the existence and significance of phaseseparated biomolecular condensates have been revealed in numerous physiological events, including cell volume perturbation. In this review, we summarize the current understanding of cell volume-sensing mechanisms, introduce recent studies on biomolecular condensates induced by cell volume change and discuss how biomolecular condensates contribute to cell volume sensing and cell volume maintenance. In addition to previous studies of biochemistry, molecular biology and cell biology, a phase separation perspective will allow us to understand the complicated volume regulatory systems of cells.

scholarly journals Phase separation and clustering of an ABC transporter in Mycobacterium tuberculosis

2019 ◽  
Vol 116 (33) ◽  
pp. 16326-16331 ◽  
Author(s):  
Florian Heinkel ◽  
Libin Abraham ◽  
Mary Ko ◽  
Joseph Chao ◽  
Horacio Bach ◽  
...  
Keyword(s):  
Mycobacterium Tuberculosis ◽  
Phase Separation ◽  
Lipid Bilayers ◽  
Abc Transporter ◽  
Single Molecule ◽  
Intracellular Signaling ◽  
Intrinsically Disordered ◽  
Regulatory Module ◽  
Condensate Formation ◽  
Associated Proteins

Phase separation drives numerous cellular processes, ranging from the formation of membrane-less organelles to the cooperative assembly of signaling proteins. Features such as multivalency and intrinsic disorder that enable condensate formation are found not only in cytosolic and nuclear proteins, but also in membrane-associated proteins. The ABC transporter Rv1747, which is important for Mycobacterium tuberculosis (Mtb) growth in infected hosts, has a cytoplasmic regulatory module consisting of 2 phosphothreonine-binding Forkhead-associated domains joined by an intrinsically disordered linker with multiple phospho-acceptor threonines. Here we demonstrate that the regulatory modules of Rv1747 and its homolog in Mycobacterium smegmatis form liquid-like condensates as a function of concentration and phosphorylation. The serine/threonine kinases and sole phosphatase of Mtb tune phosphorylation-enhanced phase separation and differentially colocalize with the resulting condensates. The Rv1747 regulatory module also phase-separates on supported lipid bilayers and forms dynamic foci when expressed heterologously in live yeast and M. smegmatis cells. Consistent with these observations, single-molecule localization microscopy reveals that the endogenous Mtb transporter forms higher-order clusters within the Mycobacterium membrane. Collectively, these data suggest a key role for phase separation in the function of these mycobacterial ABC transporters and their regulation via intracellular signaling.

Reconstitution of the complement channel into lipid vesicles and planar bilayers starting from the fluid phase complex

1985 ◽  
Vol 5 (2) ◽  
pp. 129-136 ◽  
Author(s):  
Gianfranco Menestrina ◽  
Flavia Pasquali
Keyword(s):  
Lipid Bilayers ◽  
Membrane Attack Complex ◽  
Fluid Phase ◽  
Lipid Vesicles ◽  
Ionic Channels ◽  
Single Channels ◽  
Planar Bilayers ◽  
Low Concentrations ◽  
Host Membrane ◽  
Phase Complex

Proteolysis of the fluid phase complement complex SC5b-9 transforms it into an arnphiphilic molecule which resembles the membrane attack complex of complement and reconstitutes into lipid vesicles. Complement-containing vesicles prepared in this way can be made to fuse with planar lipid bilayers transferring their protein content to the host membrane. Massive conductance increases can thus be observed, which are due to the insertion of a large number of ionic channels into the membrane. Using low concentrations of vesicles, single channels can be studied.

Fractal bet and FHH theories of adsorption: a comparative study

1989 ◽  
Vol 423 (1864) ◽  
pp. 169-188 ◽  
Keyword(s):  
Critical Evaluation ◽  
Power Laws ◽  
Wall Effects ◽  
Topological Dimension ◽  
Multilayer Adsorption ◽  
High Coverage ◽  
Adsorbed Phase ◽  
Bet Isotherm ◽  
Adsorption Of Gases ◽  
Bet Theory

Two theories of multilayer adsorption of gases, namely the BrunauerEmmett-Teller (bet) theory and the Frenkel-Halsey-Hill (fhh) theory, have recently been extended to the case of fractal substrates in a number of different ways. We present a critical evaluation of the various predictions. The principal results are the following. At high coverage, the fractal bet and fhh isotherms apply to mass and surface fractals, respectively. Both give characteristic power laws with D -dependent exponents ( D = fractal dimension of the substrate). The bet isotherm additionally depends on the topological dimension D top of the substrate. For fractal aggregates ( D top = 1) with D < 2, the adsorbed phase exists only in a highly disordered state. The bet theory is sensitive to multiple-wall effects (they affect prefactors); the fhh theory is not. For the fhh theory, detailed assessments of the approximations in the model are available. The predictions of the fhh theory have been observed on fractal silver surfaces.

scholarly journals Interactions of the designed antimicrobial peptide MB21 and truncated dermaseptin S3 with lipid bilayers: molecular-dynamics simulations

2003 ◽  
Vol 370 (1) ◽  
pp. 233-243 ◽  
Author(s):  
Craig M. SHEPHERD ◽  
Hans J. VOGEL ◽  
D. Peter TIELEMAN
Keyword(s):  
Molecular Dynamics ◽  
Antimicrobial Peptide ◽  
Molecular Dynamics Simulations ◽  
Lipid Bilayers ◽  
Helical Conformation ◽  
Constraint Forces ◽  
Surface Binding ◽  
Lipid Interactions ◽  
Area Per Lipid ◽  
Dynamics Simulations

Molecular-dynamics simulations covering 30ns of both a natural and a synthetic antimicrobial peptide in the presence of a zwitterionic lipid bilayer were performed. In both simulations, copies of the peptides were placed in an α-helical conformation on either side of the bilayer about 10Å (1Å = 0.1nm) from the interface, with either the hydrophobic or the positively charged face of the helix directed toward the bilayer surface. The degree of peptide—lipid interaction was dependent on the starting configuration: surface binding and subsequent penetration of the bilayer was observed for the hydrophobically oriented peptides, while the charge-oriented peptides demonstrated at most partial surface binding. Aromatic residues near the N-termini of the peptides appear to play an important role in driving peptide—lipid interactions. A correlation between the extent of peptide—lipid interactions and helical stability was observed in the simulations. Insertion of the peptides into the bilayer caused a dramatic increase in the lateral area per lipid and decrease in the bilayer thickness, resulting in substantial disordering of the lipid chains. Results from the simulations are consistent with early stages of proposed mechanisms for the lytic activity of antimicrobial peptides. In addition to these ‘free’ simulations, 25ns simulations were carried out with the peptides constrained at three different distances relative to the bilayer interface. The constraint forces are in agreement with the extent of peptide—bilayer insertion observed in the free simulations.

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