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Liposomes, Exosomes, and Virosomes: From Modeling Complex
Membrane Processes to Medical Diagnostics and Drug Delivery
Poster Abstracts
74
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