Orientation of Laurdan in Phospholipid Bilayers Influences Its Fluorescence: Quantum Mechanics and Classical Molecular Dynamics Study.

Mirza Wasif Baig,Lukasz Cwiklik,Jiri Pittner,Piotr Jurkiewicz,Marek Pederzoli

doi:10.3390/molecules23071707

Abstract

Fluidity of lipid membranes is known to play an important role in the functioning of living organisms. The fluorescent probe Laurdan embedded in a lipid membrane is typically used to assess the fluidity state of lipid bilayers by utilizing the sensitivity of Laurdan emission to the properties of its lipid environment. In particular, Laurdan fluorescence is sensitive to gel vs liquid–crystalline phases of lipids, which is demonstrated in different emission of the dye in these two phases. Still, the exact mechanism of the environment effects on Laurdan emission is not understood. Herein, we utilize dipalmitoylphosphatidylcholine (DPPC) and dioleoylphosphatidylcholine (DOPC) lipid bilayers, which at room temperature represent gel and liquid–crystalline phases, respectively. We simulate absorption and emission spectra of Laurdan in both DOPC and DPPC bilayers with quantum chemical and classical molecular dynamics methods. We demonstrate that Laurdan is incorporated in heterogeneous fashion in both DOPC and DPPC bilayers, and that its fluorescence depends on the details of this embedding.

Highlights

Fluorescence spectroscopy and fluorescence microscopy are key methods for studying phase behavior in biological lipid membranes [1]
Fluorescence methods often rely on membrane fluorescent probes that report on their lipid environment
These spectra are in good agreement with experimental absorption spectra measured at room temperature in water and cyclohexane for PRODAN which is the fluorescent probe having the same fluorophore as Laurdan [7]

Summary

Introduction

Fluorescence spectroscopy and fluorescence microscopy are key methods for studying phase behavior in biological lipid membranes [1]. Such a phase behavior determines mobility of membrane lipids and proteins being crucial for the functioning of living organisms. In this respect, fluorescence methods often rely on membrane fluorescent probes that report on their lipid environment. The so-called generalized polarization method [4] is frequently used to assess the fluidity of lipid membranes based on the different behavior of Laurdan emission indioleoylphosphatidylcholine (DOPC) and dipalmitoylphosphatidylcholine (DPPC) bilayers. The details of Laurdan emission in Molecules 2018, 23, 1707; doi:10.3390/molecules23071707 www.mdpi.com/journal/molecules

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Conclusion