A Lipid Photoswitch Controls Fluidity in Supported Bilayer Membranes

Abstract

Supported lipid bilayer (SLB) membranes are key elements to mimic membrane interfaces on a planar surface. Here, we demonstrate that azobenzene photolipids (azo-PC) form fluid, homogeneous SLBs. Diffusion properties of azo-PC within SLBs were probed by fluorescence microscopy and fluorescence recovery after photobleaching. At ambient conditions, we find that the trans-to-cis isomerization causes an increase of the diffusion constant by a factor of two. Simultaneous excitation with two wavelengths and variable intensities furthermore allows to adjust the diffusion constant D continuously. Xray reflectometry and small-angle scattering measurements reveal that membrane photoisomerization results in a bilayer thickness reduction of ∼0.4 nm (or 10%). While thermally induced back-switching is not observed, we find that the trans bilayer fluidity is increasing with higher temperatures. This change in diffusion constant is accompanied by a red-shift in the absorption spectra. Based on these results, we suggest that the reduced diffusivity of trans-azo-PC is controlled by intermolecular interactions that also give rise to Haggregate formation in bilayer membranes.

Optical Control of Phosphatidic Acid Signaling

“… 27 Photoswitchable lipids have yielded optical control of several biological targets, including ion channels, 28 − 30 G-protein-coupled receptors (GPCRs), 31 − 33 enzymes, 34 , 35 nuclear hormone receptors, 36 − 38 immune receptors, 39 , 40 as well as membrane properties. 41 − 46 Among the photolipids developed to date several are analogues of lipids implicated in PA metabolism, which include fatty acids ( FAAzo4 ), 28 diacylglycerol ( PhoDAG and OptoDArG ), 29 , 34 lysophosphatidic acid ( AzoLPA ), 33 and phosphatidylcholine ( AzoPC ) 44 ( Figure 1 A,B).…”

Photoswitchable Lipids

“…Together, the Nickel, Trauner and Lohmüller groups demonstrated the reversible tuning of membrane fluidity in supported lipid bilayers solely composed of AzoPC [11] . This study demonstrated that the activation energy for photolipid diffusion depends on the molecular interactions and aggregate formation.…”

“…Size and shape of the GUVs can be controlled by the lipid composition [7] . Incorporating photoswitchable lipids into GUVs allowed for the reversible control of membrane fission, [8] shape changes, [9] vesicle size, [10] bilayer fluidity, [11] bending rigidity, [8] domain formation and lipid‐lipid interactions [12] . GUVs can be manipulated, often irreversibly, by changing pH and temperature.…”

Spectroscopy of model-membrane liposome-protein systems: complementarity of linear dichroism, circular dichroism, fluorescence and SERS

“…The plotted data contains the information required to calculate lateral diffusion coefficients, which are in turn used in membrane dynamics study. FRAP has been applied for comparative study of new types of liposomes [21][22][23], fluidity of the lipid bilayers [24,25] and proteins' dynamics in the membrane [26,27]. The main limitations of FRAP are photoswitching of analyte chemical or structural analytes and localised heating by the laser [28] which can change the sample.…”