Biophysical Society Thematic Meeting | Ascona, Switzerland

Liposomes, Exosomes, and Virosomes: From Modeling Complex Membrane Processes to Medical Diagnostics and Drug Delivery

Poster Abstracts

2-POS Board 1 Laurdan and NBD-Lipids in Membranes: What Are They Actually Probing? Mariana Amaro , Piotr Jurkiewicz, Martin Hof. J. Heyrovský Institute of Physical Chemistry of A.S.C.R., v.v.i., Prague, Prague, Czech Republic. Fluorescence methods are versatile tools for obtaining dynamic and topological information about biomembranes. Laurdan and nitrobenzoxadiazole (NBD)-labelled lipids are popular fluorescent membrane probes. However, common misunderstandings of important aspects of the photophysics of both probes lead to inaccurate interpretations of experimental results. The laurdan generalized polarization (GP) function is commonly used to assess the order/hydration of model and cell membranes. Laurdan GP is often found in literature as an indicator of ‘‘extent of water penetration’’. However, GP is an empirical steady-state ratiometric parameter from which one cannot separately resolve the influence of order and hydration. Only time-dependent fluorescence shift (TDFS) measurements can reveal independently information on polarity and mobility of laurdan’s solvation shell. Here we present laurdan TDFS data which demonstrate that GP reflects predominantly the mobility of the hydrated sn -1 carbonyls (order) and not the extent of hydration of a bilayer in the liquid crystalline phase. The photophysical characteristics of NBD make it a sensitive probe and NBD-lipid analogues have found wide use in the study of biomembranes. An interesting application of NBD-lipids in membranes is the sensing of solvent relaxation by the red edge excitation shift (REES) phenomenon. REES of NBD-lipids is typically interpreted as reflecting restricted mobility of solvent surrounding the fluorophore, and thus used to infer on membrane order. Here we detail REES, TDFS and lifetime data of NBD-lipids which demonstrate that the photophysical behaviour of NBD cannot be explained by restrictions to solvent relaxation. We show that the origin of REES is the heterogeneous transverse location of the NBD probes and, therefore, that REES in not an adequate method for probing solvent relaxation/membrane order. Amaro, M.; et al., Biophys. J., (2014) 107, 12 Amaro, M.; et al., PCCP., (2016) 18

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