Photo-lipids: trans or cis ? The cover image represents AFM micrographs of phase-separated supported lipid bilayers containing an azobenzene-derived photo-lipid (top & bottom rows). The light-induced isomerization of the azobenzene allows remodeling of the shape of membrane domains. When the photo-lipid adopts a cis-configuration, a fluidification of the membrane is observed as small liquid-disordered (l_d) domains (brown) are formed inside the liquid-ordered (l_o) phase (gold). In the trans-configuration, the area of the l_o domains becomes prominent over that of the l_d phase, indicating an increase of membrane order. In the presence of a protein (middle row), cis-isomerization triggers the formation of domains enriched with protein clusters. More information can be found in the Review by Larissa Socrier and Claudia Steinem.

An optical control: The structure and organization of eukaryotic plasma membranes has been widely discussed since the introduction of the fluid mosaic model. Light-sensitive lipids were recently introduced in artificial lipid systems and cells to study lipid-lipid and lipid-protein interactions. Here, we review the application of these probes to investigate membrane properties and lateral organization.

Abstract

Biological membranes are described as a complex mixture of lipids and proteins organized according to thermodynamic principles. This chemical and spatial complexity can lead to specialized functional membrane domains enriched with specific lipids and proteins. The interaction between lipids and proteins restricts their lateral diffusion and range of motion, thus altering their function. One approach to investigating these membrane properties is to use chemically accessible probes. In particular, photo-lipids, which contain a light-sensitive azobenzene moiety that changes its configuration from trans- to cis- upon light irradiation, have recently gained popularity for modifying membrane properties. These azobenzene-derived lipids serve as nanotools for manipulating lipid membranes in vitro and in vivo. Here, we will discuss the use of these compounds in artificial and biological membranes as well as their application in drug delivery. We will focus mainly on changes in the membrane's physical properties as well as lipid membrane domains in phase-separated liquid-ordered/liquid-disordered bilayers driven by light, and how these changes in membrane physical properties alter transmembrane protein function.