A Lipid Photoswitch Controls Fluidity in Supported Bilayer Membranes
Patrick Urban, Stefanie D. Pritzl, Martina F. Ober, Christina F. Dirscherl, Carla Pernpeintner, David B. Konrad, James A. Frank, Dirk Trauner, Bert Nickel, Theobald Lohmueller
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. X-ray 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 H-aggregate formation in bilayer membranes.