Phase separation and near-critical fluctuations in two-component lipid membranes: Monte Carlo simulations on experimentally relevant scales

By means of lattice-based Monte Carlo simulations, we address properties of two-component lipid membranes on the experimentally relevant spatial scales of order of a micrometer and time intervals of order of a second, using DMPC/DSPC lipid mixtures as a model system. Our large-scale simulations allowed us to obtain important results previously not reported in simulation studies of lipid membranes. We find that, within a certain range of lipid compositions, the phase transition from the fluid phase to the fluid-gel phase coexistence proceeds via near-critical fluctuations, while for other lipid compositions this phase transition has a quasi-abrupt character. In the presence of near-critical fluctuations, transient subdiffusion of lipid molecules is observed. These features of the system are stable with respect to perturbations in lipid interaction parameters used in our simulations. The line tension characterizing lipid domains in the fluid-gel coexistence region is found to be in the pN range. When approaching the critical point, the line tension, the inverse correlation length of fluid-gel spatial fluctuations, and the corresponding inverse order parameter susceptibility of the membrane vanish. All these results are in agreement with recent experimental findings for model lipid membranes. Our analysis of the domain coarsening dynamics after an abrupt quench of the membrane to the fluid-gel coexistence region reveals that lateral diffusion of lipids plays an important role in the fluid-gel phase separation process.Comment: 45 pages, 15 figure

Near-critical fluctuations and cytoskeleton-assisted phase separation lead to subdiffusion in cell membranes

We address the relationship between membrane microheterogeneity and anomalous subdiffusion in cell membranes by carrying out Monte Carlo simulations of two-component lipid membranes. We find that near-critical fluctuations in the membrane lead to transient subdiffusion, while membrane-cytoskeleton interaction strongly affects phase separation, enhances subdiffusion, and eventually leads to hop diffusion of lipids. Thus, we present a minimum realistic model for membrane rafts showing the features of both microscopic phase separation and subdiffusion.Comment: 21 pages, 5 figures; Supporting Material 5 pages, 1 figure, 1 tabl

Focus on the physics of the cell membrane

This focus issue on membrane biophysics presents a collection of papers illustrating new developments in modern biophysical research on cell membranes. The work described here addresses questions from a broad range of areas, including cell adhesion, membrane trafficking and activation of cells of the immune system. It also presents recent views on membrane mechanics, the effect of electric fields, as well as on the interplay of mechanics and chemistry and organization at many different scales

Zwei-Photonen-Kreuzkorrelations-Spektroskopie : Nachweis der Interaktionen einzelner Moleküle in der lebenden Zelle

The progress of miniaturisation towards the nanoscopic scale in science and technology has also influenced the biosciences. This is particularly important, since proteins, as the smallest functional units of life, exhibit a spectacular wealth of functionalities, enabling them to fulfil complex tasks in cells and organisms. For this reason, they are often termed molecular or cellular “machines”. To be able to investigate and better understand these fascinating molecules in their native environment, new analytical methods must be developed, with appropriately high sensitivity and spatial and temporal resolution. We describe one very promising technique based on fluorescence spectroscopy, which allows a quantitative analysis of protein- protein interactions in the live cell.Die zunehmende Miniaturisierung bis hin zum nanoskopischen Maßstab in vielen technischen Disziplinen hat auch die Lebenswissenschaften ergriffen. Dies ist insofern von großer Bedeutung, als die Proteine als kleinste funktionale Einheiten des Lebens trotz ihrer winzigen Abmessungen eine faszinierende Komplexität aufweisen, die es ihnen erlauben, hoch differenzierte und spezialisierte Aufgaben in der Zelle und im Organismus zu übernehmen. Aus diesem Grund werden sie in der modernen Biologie auch als molekulare oder zelluläre „Maschinen“ bezeichnet. Um diese kleinen Wunderwerke zu studieren und ihre Funktionsweise in ihrer natürlichen Umgebung zu analysieren, bedarf es innovativer Technologien, die es erlauben, mit maximaler räumlicher und zeitlicher Auflösung auch einzelne Moleküle in der lebenden Zelle sichtbar zu machen und zu verfolgen. Im Folgenden wird eine von uns entwickelte fluoreszenzspektroskopische Methode vorgestellt, mit deren Hilfe die komplizierten Interaktionen zwischen Proteinen in der lebenden Zelle aufgeklärt werden können

Translational and rotational diffusion of micrometer-sized solid domains in lipid membranes

We use simultaneous observation of translational and rotational Brownian motion of domains in lipid membranes to test the hydrodynamics-based theory for the viscous drag on the membrane inclusion. We find that translational and rotational diffusion coefficients of micrometer-sized solid (gel-phase) domains in giant unilamellar vesicles showing fluid–gel phase coexistence are in excellent agreement with the theoretical predictions.Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich