Laurdan discerns lipid membrane hydration and cholesterol content

Abstract

Studies of biological membrane heterogeneity particularly benefit from the use of the environment-sensitive fluorescent probe Laurdan, for which shifts in the emission, produced by any stimulus (e.g. fluidity variations), are ascribed to alterations in hydration near the fluorophore. Ironically, no direct measure of the influence of membrane hydration level on Laurdan spectra has been available. To address this, we investigated the fluorescence spectrum of Laurdan embedded in solid-supported lipid bilayers as a function of hydration and compared it with the effect of cholesterol, a major membrane fluidity regulator. The effects are illusively similar, hence the results obtained with this probe should be interpreted with caution. The dominant phenomenon governing the changes in the spectrum is the hindrance of the lipid internal dynamics. Furthermore, we unveiled the intriguing mechanism of dehydration-induced redistribution of cholesterol between domains in the phase-separated membrane which reflects yet another regulatory function of cholesterol.

FRET-GP – A Local Measure of the Impact of Transmembrane Peptide on Lipids

“…Exclusive changes in lipid hydration are rare and difficult to achieve. 44 As shown in Figure S3, our GP values represent the rate of dipolar relaxation rather than hydration. This is a common pattern found in our studies using TDFS, 45 where we showed that in contrast to peripheral peptide binding, which has little effects on Laurdan, transmembrane peptides reduce lipid mobility without affecting membrane hydration.…”

Nanoscale structural response of biomimetic cell membranes to controlled dehydration

“…Recently, we presented a novel method for membrane preservation under dehydration conditions based on the controlled steady decrease of environmental humidity, which provides new possibilities to study the behavior and properties of membranes without altering their chemical composition or physical features. 37,38 In this study, we have used a combination of fluorescence and atomic force microscopy to investigate the nanoscale structural response of phase-separated SLBs to a wide range of hydration conditions. Our results demonstrate that the structure of lipid membranes can be preserved even under conditions of complete desiccation without the use of stabilising agents, if the dehydration process is carried out in a gradual and controlled manner.…”

Dehydration of Lipid Membranes Drives Redistribution of Cholesterol Between Lateral Domains

“…23 Importantly, the values we report here are in full quantitative agreement with the partitioning coefficient of native cholesterol between coexisting L o and L d phases (∼0.7 and ∼0.3, respectively) in fully hydrated SLBs of the same composition. 25 Consequently, it can be inferred that, under these specific conditions, TopFluor-Chol accurately mimics native choles-terol in terms of its lateral distribution in the phase-separated lipid bilayer.…”

“…The cholesterol influx from the L o domains into surrounding unsaturated lipid-rich regions rationalizes well the phenomenon observed in our previous experimental study using the environment-sensitive fluorescent probe Laurdan. 25 In brief, we compared changes of the L d phase's fluidity, determined from the Laurdan emission spectrum, as a function of the hydration state of two types of SLBs: (i) a membrane with coexisting L d and L o domains, identical in composition to the current study, but with only Atto 633-DOPE and Laurdan as fluorescent labels (so Chol was native, untagged), and (ii) a single-phase membrane with the same molecular composition as the L d phase in the phase-separated membrane (containing 0.3 mol fraction of Chol). While the two systems were compositionally identical under fully hydrated conditions, dehydration yielded disparate results.…”

“…Consequently, this reduction produces an energy gain, facilitating the formation of the subsequent stalk intermediate. Furthermore, cholesterol counteracts the dehydration-induced extensive changes in fluidity of the nonraft membrane regions, 25 thus creating a more favorable environment for the fusion.…”