Figure 2 - uploaded by Frederick Heberle
Content may be subject to copyright.
Lattice snapshots for Monte Carlo simulations of ternary mixtures. (E) An equimolar binary a/b mixture with an unfavorable pairwise interaction energy DE ab ¼ 0.8kT is characterized by coexistence of a-rich and b-rich phases. (A-D) Although maintaining the ratio of components a and b, a third component, g (which could be cholesterol), is added that interacts favorably with both a and b (DE ag ¼20.8 kT, DE bg ¼ 21.2 kT). (D) At x g ¼ 0.20, large clusters of b within the a-rich phase (and vice versa) are evident. (C) Long-range structure is broken up at x g ¼ 0.25. An enlargement of the snapshot (F) shows clusters of hundreds of lipids, and the uneven distribution of component g (gray) between a-rich (white) and b-rich (black) clusters. Further addition of component g reduces the size of clusters. (B) Snapshot for x g ¼ 0.30 and (A) x g ¼ 0.35.
Source publication
Cell membranes show complex behavior, in part because of the large number of different components that interact with each other in different ways. One aspect of this complex behavior is lateral organization of components on a range of spatial scales. We found that lipid-only mixtures can model the range of size scales, from approximately 2 nm up to...
Contexts in source publication
Context 1
... insight into lipid mixing comes from considering the more complex behavior of multicomponent bilayer mixtures. Figure 2 shows snapshots of mixing behavior in which the interaction energies are held constant, but the concentration of a third component is Figure 2E. In these simulations, increasing cho- lesterol concentration leads to increased mixing of the components. At a cholesterol concentra- tion of 35 mol % the mixture shows highly non- random mixing, with clusters of approximately 20 lipids (Fig. 2A). Smaller cholesterol concen- trations lead to increasing cluster sizes. For example, Figure 2C,F show clusters of several hundreds of lipids at 25 mol % cholesterol, cor- responding to a domain size of approximately 10 ...
Context 2
... insight into lipid mixing comes from considering the more complex behavior of multicomponent bilayer mixtures. Figure 2 shows snapshots of mixing behavior in which the interaction energies are held constant, but the concentration of a third component is Figure 2E. In these simulations, increasing cho- lesterol concentration leads to increased mixing of the components. At a cholesterol concentra- tion of 35 mol % the mixture shows highly non- random mixing, with clusters of approximately 20 lipids (Fig. 2A). Smaller cholesterol concen- trations lead to increasing cluster sizes. For example, Figure 2C,F show clusters of several hundreds of lipids at 25 mol % cholesterol, cor- responding to a domain size of approximately 10 ...
Context 3
... insight into lipid mixing comes from considering the more complex behavior of multicomponent bilayer mixtures. Figure 2 shows snapshots of mixing behavior in which the interaction energies are held constant, but the concentration of a third component is Figure 2E. In these simulations, increasing cho- lesterol concentration leads to increased mixing of the components. At a cholesterol concentra- tion of 35 mol % the mixture shows highly non- random mixing, with clusters of approximately 20 lipids (Fig. 2A). Smaller cholesterol concen- trations lead to increasing cluster sizes. For example, Figure 2C,F show clusters of several hundreds of lipids at 25 mol % cholesterol, cor- responding to a domain size of approximately 10 ...
Context 4
... insight into lipid mixing comes from considering the more complex behavior of multicomponent bilayer mixtures. Figure 2 shows snapshots of mixing behavior in which the interaction energies are held constant, but the concentration of a third component is Figure 2E. In these simulations, increasing cho- lesterol concentration leads to increased mixing of the components. At a cholesterol concentra- tion of 35 mol % the mixture shows highly non- random mixing, with clusters of approximately 20 lipids (Fig. 2A). Smaller cholesterol concen- trations lead to increasing cluster sizes. For example, Figure 2C,F show clusters of several hundreds of lipids at 25 mol % cholesterol, cor- responding to a domain size of approximately 10 ...
Context 5
... lipid clusters grow as the mixture is changed to approach a boundary of phase sep- aration, but only in a limited way: Cluster sizes approach a maximal range that is similar for the mixtures with different numbers of compo- nents. However, a short distance past the phase boundary in composition space (Fig. 2) or in energy (Fig. 1) results in enormous, abrupt change in size of ...
Similar publications
The precise imaging of biomolecular entities contributes to an understanding of the relationship between their structure and function. However, the resolution of conventional infrared microscopic imaging is diffraction limited and does not exceed a few micrometres. Atomic force microscopy, on the other hand, can detect infrared absorption down to t...
The c-Src oncogene is anchored to the cytoplasmic membrane through its N-terminal myristoylated SH4 domain. This domain is part of an intramolecular fuzzy complex with the SH3 and Unique domains.
Here we show that the N-terminal myristoyl group binds to the SH3 domain in the proximity of the RT loop, when Src is not anchored to a lipid membrane. Re...
Environment-sensitive probes constitute powerful tools for monitoring changes in the physico-chemical properties of cell plasma membranes. Among these probes, 3-hydroxyflavone probes are of great interest due to their dual emission and ratiometric response. Here, three probes derived from the parent F2N12S were designed, characterized and applied t...
Thermally induced shape fluctuations of giant quasi-spherical lipid
vesicles are used to study the influence of the cholesterol,
incorporated in the lipid membranes, on the bending elasticity modulus
kc of the lipid membrane. The influence of cholesterol is
investigated throughout a considerably wide interval of concentrations.
The values of the be...
Citations
... For this reason, the introduction of a phase-separation diffusive model able to predict coalescence of different species becomes apparent. Within this framework, the Cahn-Hilliard equation is typically used to describe two-phase separation problems [64][65][66] that are mathematically described by a diffusion equation for the species concentration [67]. In this respect, the theoretical model proposed in [40] described the evolution of protein species through Cahn-Hilliard-like energetics and kinetics wherein reaction interspecific terms account for the mutual influence among protein populations, i.e. the above mentioned GPCRs and their antagonist the Multidrug Resistance Proteins (MRPs), while non-local species momenta are enriched by strain-dependent morphotaxis terms. ...
Plasma membranes appear as deformable systems wherein molecules are free to move and diffuse giving rise to condensed microdomains (composed of ordered lipids, transmembrane proteins and cholesterol) surrounded by disordered lipid molecules. Such denser and thicker regions, namely lipid rafts, are important communication hubs for cells. Indeed, recent experiments revealed how the most of active signaling proteins co-localize on such domains, thereby intensifying the biochemical trafficking of substances. From a material standpoint, it is reasonable to assume the bilayer as a visco-elastic body accounting for both in-plane fluidity and elasticity. Consequently, lipid rafts contribute to membrane heterogeneity by typically exhibiting higher stiffness and viscosity and by locally altering the bilayer dynamics and proteins activity. A chemo-mechanical model of lipid bilayer coupled with interspecific dynamics among the resident species (typically transmembrane receptors and trasporters) has been recently formulated to explain and predict how proteins regulate the dynamic heterogeneity of membrane. However, the explicit inclusion of the membrane viscosity in the model was not considered. To this aim, the present work enriches the constitutive description of the bilayer by modeling its visco-elastic behavior. This is done through a strain-level dependent viscosity able to theoretically trace back the alteration of membrane fluidity experimentally observed in lipid phase transitions. This provides new insights into how the quasi-solid and fluid components of lipid membrane response interact with the evolution of resident proteins by affecting the activity of raft domains, with effects on cell mechano-signaling.
... An inherent challenge in such simple mixtures is the potential for undesirable phase behavior (e.g., phase transition from liquid-disordered to liquid-ordered or the gel) in the membrane, even when the primary components of the biological membrane are reasonably represented. 61,62 This may happen because the absence of active mechanisms found in living organisms that maintain membrane integrity. 61,62 So, when using model mixtures, we need to carefully ensure that the membrane remains in its fluid phase. ...
... 61,62 This may happen because the absence of active mechanisms found in living organisms that maintain membrane integrity. 61,62 So, when using model mixtures, we need to carefully ensure that the membrane remains in its fluid phase. To this end, we found that we could not use majority myristoyl chains (14:0), exactly because the corresponding bilayer membrane undergoes phase transition into a gel phase, as evidenced by the decrease in APL from is 65.1 Å +/-1.00 ...
Molecular dynamics simulations are used to interrogate the dynamic nature of Staphylococcus aureus Type I signal peptidases, SpsA and SpsB, including the impact of the P29S mutation of SpsB. Fluctuations and plasticity-rigidity characteristics vary among the proteins, particularly in the extracellular domain. Intriguingly, the P29S mutation, which influences susceptibility to arylomycin antibiotics, affect the mechanically coupled motions in SpsB. The integrity of the active site is crucial for catalytic competency, and variations in sampled structural conformations among the proteins are consistent with diverse peptidase capabilities. We also explored the intricate interactions between the proteins and the model S. aureus membrane. It was observed that certain membrane-inserted residues in the loop around residue 50 (50s) and C-terminal loops, beyond the transmembrane domain, give rise to direct interactions with lipids in the bilayer membrane. Our findings are discussed in the context of functional knowledge about these signal peptidases, offering additional understanding of dynamic aspects relevant to some cellular processes with potential implications for drug targeting strategies.
Highlights
Dynamics of S. aureus SpsA and SpsB (wild-type and P29S) is analyzed.
Differences in flexibility and plasticity are relevant for function.
P29S mutation decouples mechanical motions in SpsB.
Extracellular domain loops insert differently into the membrane in SpsA and SpsB.
S. aureus model membrane properties are elucidated.
... Accumulated experimental evidence accumulated for different cell types suggests that the pyramidal shape of neuronal soma is a direct result of such bidirectional impact. The size scales range for protein-lipid tetrahedral complexes can be from several nanometers to several microns [199,[215][216][217][218][219][220][221][222]. Despite such a size is smaller than size of PyrNs soma, these experimental facts point to principal opportunity for the molecular structure to form the corners of pyramidal soma. ...
... Despite such a size is smaller than size of PyrNs soma, these experimental facts point to principal opportunity for the molecular structure to form the corners of pyramidal soma. From a formal geometrical view, it is possible to compose a 3-D tetrahedral structure of unlimited size (Figure 1] from the small tetrahedral units [221]. Notably, that chirality of elementary trihedron can be transferred to the lager-scale structure. ...
The mechanism of brain information processing unfolds within spatial and temporal domains inherently linked to the concept of symmetry. Biological evolution, beginning with the prevalent molecular chirality, results in the handedness of cognitive and psychological functions (the phenomena known as biochirality). The key element in the chain of chirality transfer from the downstream to upstream processes is the pyramidal neuron (PyrN) morphology-function paradigm (archetype). The most apparent landmark of PyrN is the geometry of the cell soma. However, “why/how PyrN soma gains the shape of quasi-tetrahedral symmetry” has never been explicitly articulated. Resolving the above inquiry is only possible based on the broad-view assumption that encoding 3D-space requires specific 3D-geometry of the neuronal detector and corresponding network. Accordingly, our hypothesis states that if the primary function of PyrNs, at the organism level, is sensory space perception, then the pyramidal shape of soma is the best evolutionary-selected geometry to support sensory-motor coupling.
... In particular, the Cahn-Hilliard is a phenomenological equation commonly used to describe two-phase biological systems (Cherfils et al. 2014). Among these, a particular attention is on cellular membrane that can be represented as a multicomponent bilayer mixture in which lipids and proteins coexist in two different phases (Heberle and Feigenson 2011). Indeed, lipid membranes experience phase transition between ordered and disorder phase and thus, lipid bilayer models should also include phase separation (Elson et al. 2010). ...
Cell membranes, mediator of many biological mechanisms from adhesion and metabolism up to mutation and infection, are highly dynamic and heterogeneous environments exhibiting a strong coupling between biochemical events and structural re-organisation. This involves conformational changes induced, at lower scales, by lipid order transitions and by the micro-mechanical interplay of lipids with transmembrane proteins and molecular diffusion. Particular attention is focused on lipid rafts, ordered lipid microdomains rich of signalling proteins, that co-localise to enhance substance trafficking and activate different intracellular biochemical pathways. In this framework, the theoretical modelling of the dynamic clustering of lipid rafts implies a full multiphysics coupling between the kinetics of phase changes and the mechanical work performed by transmembrane proteins on lipids, involving the bilayer elasticity. This mechanism produces complex interspecific dynamics in which membrane stresses and chemical potentials do compete by determining different morphological arrangements, alteration in diffusive walkways and coalescence phenomena, with a consequent influence on both signalling potential and intracellular processes. Therefore, after identifying the leading chemo-mechanical interactions, the present work investigates from a modelling perspective the spatio-temporal evolution of raft domains to theoretically explain co-localisation and synergy between proteins’ activation and raft formation, by coupling diffusive and mechanical phenomena to observe different morphological patterns and clustering of ordered lipids. This could help to gain new insights into the remodelling of cell membranes and could potentially suggest mechanically based strategies to control their selectivity, by orienting intracellular functions and mechanotransduction.
... We use large unilamellar vesicles (LUV) and small unilamellar vesicles (SUV) of around 200 and 30 nm diameter each made with either 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)(Table S1) to achieve constant membrane curvature or lipid mixture 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC), 1,2-dioleoyl-sn-glycero-3-phosphoethanolamine (DOPE), and cholesterol (Chol, ratio of 2:1:2)(Table S1) with heterogeneous phases of varying localized curvatures. 59,[62][63][64] To screen for binding, ensemble measurements and single molecule localization microscopy are used and report on which steric factors of DNP and membrane vesicles influence binding yield ( Figure 1D). ...
Rigid DNA nanostructures that bind to floppy bilayer membranes are of fundamental interest as they replicate biological cytoskeletons for synthetic biology, biosensing, and biological research. Here, we establish principles underpinning the controlled interaction of DNA structures and lipid bilayers. As membrane anchors mediate interaction, more than 20 versions of a core DNA nanostructure are built each carrying up to five individual cholesterol anchors of different steric accessibility within the 3D geometry. The structures binding to membrane vesicles of tunable curvature is determined with ensemble methods and by single-molecule localization microscopy. This screen yields quantitative and unexpected insight on which steric anchor points cause efficient binding. Strikingly, defined nanostructures with a single molecular anchor discriminate effectively between vesicles of different nanoscale curvatures which may be exploited to discern diagnostically relevant membrane vesicles based on size. Furthermore, we reveal anchor-mediated bilayer interaction to be co-controlled by non-lipidated DNA regions and localized membrane curvatures stemming from heterogenous lipid composition, which modifies existing biophysical models. Our study extends DNA nanotechnology to control interactions with bilayer membranes and thereby facilitate the design of nanodevices for vesicle-based diagnostics, biosensing, and protocells.
... The former typically separate into coexisting liquid-disordered (Ld) and liquid-ordered (Lo) phases (7,8), while the latter are invariably in a uniform Ld phase (9). For outer leaflet mixtures, the construction of ternary phase diagrams has greatly added to our understanding of how lipid and sterol structure influences the types of phases that can coexist and the location of phase boundaries (10). For organisms that regulate temperature, lipid composition is a key thermodynamic variable that could allow for control over membrane phase state (7), and compositional phase diagrams facilitate predictions for phases and phase transitions that could ...
We have determined the partial leaflet–leaflet phase diagram of an asymmetric lipid bilayer at ambient temperature using asymmetric giant unilamellar vesicles (aGUVs). Symmetric GUVs with varying amounts of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine and DOPC (1,2-dioleoyl-sn-glycero-3-phosphocholine) were hemifused to a supported lipid bilayer (SLB) composed of DOPC, resulting in lipid exchange between their outer leaflets. The GUVs and SLB contained a red and green lipid fluorophore, respectively, thus enabling the use of confocal fluorescence imaging to determine both the extent of lipid exchange (quantified for individual vesicles by the loss of red intensity and gain of green intensity) and the presence or absence of phase separation in aGUVs. Consistent with previous reports, we found that hemifusion results in large variation in outer leaflet exchange for individual GUVs, which allowed us to interrogate the phase behavior at multiple points within the asymmetric composition space of the binary mixture. When initially symmetric GUVs showed coexisting gel and fluid domains, aGUVs with less than ~50% outer leaflet exchange were also phase-separated. In contrast, aGUVs with greater than 50% outer leaflet exchange were uniform and fluid. In some cases, we also observed three coexisting bilayer-spanning phases: two registered phases and an anti-registered phase. These results suggest that a relatively large unfavorable midplane interaction between ordered and disordered phases in opposing leaflets (i.e., a midplane surface tension) can overwhelm the driving force for lateral phase separation within one of the leaflets, resulting in an asymmetric bilayer with two uniformly mixed leaflets that is poised to phase-separate upon leaflet scrambling.
... The Janus GUVs were produced using electroformation [32][33][34] as described in detail in the Methods section, and shown in Fig.1a. Briefly, using an AC electric field, we hydrate in a solution of 25 mM of sucrose at 60°C a previously dried layer of a ternary lipid mixture: 1,2-dioleoyl-sn-glycerol-3-phosphocholine (DOPC), 1,2-dipalmitoyl-snglycerol-3-phosphocholine (DPPC), and cholesterol (Chol), leading to compositionally symmetric GUVs [35,36] (Supplementary Fig.S1). While cholesterol is miscible in both lipids at a broad range of temperatures, at the chosen composition DOPC and DPPC exhibit spontaneous phase 3 separation below 30°C, forming DOPC-rich liquid disordered (L d ) and DPPC-rich liquid-ordered (L o ) phases due to the phospholipids unsaturated or saturated nature, with the latter allowing higher packing at lower temperatures [37,38]. ...
Active colloidal systems have emerged as promising contenders for the future of microdevices. While conventional designs have extensively exploited the use of hard colloids, the advancement of cell-inspired architectures represents a pivotal path towards realizing self-regulating and highly functional artificial microswimmers. In this work, we fabricate and actuate Janus lipid vesicles demonstrating reconfigurable motion under an AC electric field. The giant unilamellar vesicles (GUVs) undergo spontaneous phase separation at room temperature leading to Janus-like GUVs with two distinct lipid phases. We report self-propulsion of the Janus GUVs via induced charge electroosmosis, in between parallel electrodes. Remarkably, the fluid nature of the lipid membrane affected by the electric field leads to asymmetry-symmetry transient states resulting in run-and-tumble events supported by structure domain analysis. We characterise an enhanced rotational diffusivity associated with tumble events, decoupled from thermal reorientation. Lastly, we identify cargo-release capabilities and a variety of shape-encoded dynamic modes in these vesicles. This cell-inspired architecture provides an alternative route for creating motile artificial cells and programmable microswimmers.
... Larger lipid nanobubbles (smaller membrane curvature) would have more obvious membrane phase separation, which was further validated by quantifying the normalized lateral contacts of unsaturated lipids (Fig. 4b) as well as cholesterol preferences (Fig. 4c). As is known, for the phase separated lipid bilayer system, membrane domains have both the intra-leaflet [43,[45][46][47] and inter-leaflet [48][49][50][51][52][53][54] dynamics. Usually, these two kinds of membrane domain dynamics are closely related to each other. ...
Lipid nanobubbles have shown a great potential to be used for the ultrasound molecular imaging and biocompatible drug and gene delivery carriers, which integrate the advantages of both the biocompatibility of lipids and potent physicochemical properties of nanobubbles. Molecular dynamics (MD) simulation provides a powerful tool to investigate fundamental scientific problems related to lipid nanobubbles. With coarse-grained models, the system can be simulated with longer time scale and larger length scale. However, there are very few coarse-grained gas models for lipid nanobubble simulations. Hence, in this work, we developed a simple coarse-grained nitrogen gas model within Martini force field by adjusting the Lennard-Jones interactions of with itself, water, lipids, which well reproduced the density of pure , the density of within nanobubbles, and the partitioning thermodynamics of in DPPC bilayers. Further lipid nanobubble self-assembly simulation validated the reliability of our coarse-grained parameters. Using three-component lipid nanobubbles consisting of 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), 1,2-dilinoleoyl-sn-glycero-3-phosphocholine (DUPC), and cholesterol, our coarse-grained MD simulations indicated that single-layer membranes could also have clear phase separation, the degree of which was proportional to the radius () of the lipid nanobubble, and reached the maximum when → ∞ (the planar lipid bi-monolayer at the gas-water interface). Besides, by comparing the planar lipid bi-monolayer (at gas-water interface) and lipid bilayer systems, we found that the latter had much less obvious phase separation. In short, our coarse-grained MD simulations using systems of lipid nanobubbles, lipid bi-monolayers and lipid bilayers will provide useful insights into the role of membrane curvature and interleaflet coupling in the phase separation of multi-component lipid membranes.
... Phase separation is a fundamental process that occurs in multicomponent lipid membranes with substantial unfavorable interactions among their lipid components [13]. In such membranes, segregation of lipids based on their favorable interactions leads to phase separation. ...
This paper studies the fusogenicity of cationic liposomes in relation to their surface distribution of cationic lipids and utilizes membrane phase separation to control this surface distribution. It is found that concentrating the cationic lipids into small surface patches on liposomes, through phase-separation, can enhance liposome’s fusogenicity. Further concentrating these lipids into smaller patches on the surface of liposomes led to an increased level of fusogenicity. These experimental findings are supported by numerical simulations using a mathematical model for phase-separated charged liposomes. Findings of this study may be used for design and development of highly fusogenic liposomes with minimal level of toxicity.
... The inspiration for the lipid-raft concept emerges from the observation that artificial membranes with specific compositions of phospholipids and cholesterol can undergo phase separation into liquid-ordered (L o ) and liquiddisordered (L d ) domains (for reviews, see Recktenwald and McConnell 2002;Subczynski and Kusumi 2003;Simons and Vaz 2004;Heberle and Feigenson 2011). In the development of the raft hypothesis, artificial membrane systems such as supported membrane monolayers (Dietrich et al. 2001) and giant unilamellar vesicles (GUVs) (Bagatolli et al. 2003) played important roles. ...
The cell membrane, the boundary that separates living cells from their environment, has been the subject of study for over a century. The fluid-mosaic model of Singer and Nicolson in 1972 proposed the plasma membrane as a two-dimensional fluid composed of lipids and proteins. Fifty years hence, advances in biophysical and biochemical tools, particularly optical imaging techniques, have allowed for a better understanding of the physical nature, organization, and composition of cell membranes. This has been made possible by visualizing membrane heterogeneities and their dynamics and appreciating the asymmetrical arrangement of lipids in living cell membranes. Despite these advances, mechanisms underlying the local spatiotemporal organization of membrane components remain unclear. This review surveys various models of membrane organization, culminating in a new model that incorporates nonequilibrium processes and forces exerted by interactions with extramembrane elements such as the actin cytoskeleton. The proposed model provides a comprehensive understanding of membrane organization, taking into account the dynamic nature of the cell membrane and its interactions with its immediate environment.
