The plasma membrane is a complex system, consisting of two layers of lipids and proteins compartmentalized into small structures called nanodomains. Despite the asymmetric composition of both leaflets, coupling between the layers is surprisingly strong. This can be evidenced, for example, by recent experimental studies performed on phospholipid giant unilamellar vesicles showing that nanodomains formed in the outer layer are perfectly registered with those in the inner leaflet. Similarly, microscopic phase separation in one leaflet can induce phase separation in the opposing leaflet that would otherwise be homogeneous. In this review, we summarize the current theoretical and experimental knowledge that led to the current view that domains are - irrespective of their size - commonly registered across the bilayer. Mechanisms inducing registration of nanodomains suggested by theory and calculations are discussed. Furthermore, domain coupling is evidenced by experimental studies based on the sparse number of methods that can resolve registered from independent nanodomains. Finally, implications that those findings using model membrane studies might have for cellular membranes are discussed.

• Keywords
• biomembranes, domain registration, interleaflet coupling, membrane asymmetry, nanodomains, phase separation, plasma membranes,
• Publication type
• Journal Article MeSH
• Review MeSH

In the present work we introduce a straightforward fluorescent assay that can be applied in studies of the transbilayer movement (flip-flop) of fluorescent lipid analogues across supported phospholipid bilayers (SPBs). The assay is based on the distance dependent fluorescence quenching by light absorbing surfaces. Applied to SPBs this effect leads to strong differences in fluorescence lifetimes when the dye moves from the outer lipid leaflet to the leaflet in contact with the support. Herein, we present the basic principles of this novel approach, and comment on its advantages over the commonly used methods for investigating flip-flop dynamics across lipid bilayers. We test the assay on the fluorescent lipid analog Atto633-DOPE and the 3-hydroxyflavone F2N12S probe in SPBs composed of DOPC/ DOPS lipids. Moreover, we compare and discuss the flip-flop rates of the probes with respect to their lateral diffusion coefficients.

• MeSH
• Time Factors MeSH
• Chemistry Techniques, Analytical methods   MeSH
• Diffusion MeSH
• Fluorescence * MeSH
• Fluorescent Dyes chemistry   MeSH
• Phosphatidylcholines chemistry   MeSH
• Phosphatidylethanolamines chemistry   MeSH
• Phosphatidylserines chemistry   MeSH
• Phospholipids chemistry   MeSH
• Kinetics MeSH
• Lipid Bilayers chemistry   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• 1,2-dielaidoylphosphatidylethanolamine MeSH Browser
• 1,2-dioleoylphosphatidylserine MeSH Browser
• 1,2-oleoylphosphatidylcholine MeSH Browser
• Fluorescent Dyes MeSH
• Phosphatidylcholines MeSH
• Phosphatidylethanolamines MeSH
• Phosphatidylserines MeSH
• Phospholipids MeSH
• Lipid Bilayers MeSH

Fluorescence correlation spectroscopy (FCS) is a single molecule technique used mainly for determination of mobility and local concentration of molecules. This review describes the specific problems of FCS in planar systems and reviews the state of the art experimental approaches such as 2-focus, Z-scan or scanning FCS, which overcome most of the artefacts and limitations of standard FCS. We focus on diffusion measurements of lipids and proteins in planar lipid membranes and review the contributions of FCS to elucidating membrane dynamics and the factors influencing it, such as membrane composition, ionic strength, presence of membrane proteins or frictional coupling with solid support.

• Keywords
• biomembranes, confocal microscopy, fluorescence fluctuation spectroscopy, giant unilamellar vesicles, lateral diffusion, supported lipid bilayers,
• MeSH
• Diffusion MeSH
• Spectrometry, Fluorescence * MeSH
• Microscopy, Confocal MeSH
• Lipid Bilayers chemistry   MeSH
• Membrane Lipids chemistry   MeSH
• Unilamellar Liposomes chemistry   MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Names of Substances
• Lipid Bilayers MeSH
• Membrane Lipids MeSH
• Unilamellar Liposomes MeSH