Structural Diversity of Photoswitchable Sphingolipids for Optodynamic Control of Lipid Raft Microdomains

Abstract

Sphingolipids are a structurally diverse class of lipids predominantly found in the plasma membrane of eukaryotic cells. These lipids can laterally segregate with other saturated lipids and cholesterol into lipid rafts; liquid-ordered (Lo) microdomains that act as organizing centers within biomembranes. Owing the vital role of sphingolipids for lipid segregation, controlling their lateral localization is of utmost significance. Hence, we made use of the light-induced trans-cis isomerization of azobenzene-modified acyl chains, to develop a set of photoswitchable sphingolipids, with different headgroups (hydroxyl, galactosyl, phosphocholine) and backbones (sphingosine, phytosphingosine, tetrahydropyran (THP)-blocked sphingosine), able to shuttle between liquid-ordered (Lo) and liquid-disordered (Ld) regions of model membranes upon irradiation with UV-A (λ = 365 nm) and blue (λ = 470 nm) light, respectively. Using combined high-speed atomic force microscopy, fluorescence microscopy, and force spectroscopy, we investigated how these active sphingolipids laterally remodel supported bilayers upon photo-isomerization, notably in terms of domain area changes, height mismatch, line tension, and membrane piercing. Hereby, we show that all sphingosine- (Azo-β-Gal-Cer, Azo-SM, Azo-Cer) and phytosphingosine-based (Azo-α-Gal-PhCer, Azo-PhCer) photolipids behave similarly, promoting a reduction in Lo domain area when in the UV-adapted cis-isoform. In contrast, azo-sphingolipids having THP groups that block H-bonding at the sphingosine backbone (Azo-THP-SM, Azo-THP-Cer) induce an increase in the Lo domain area when in cis, accompanied by a major rise in height mismatch and line tension. These changes were fully reversible upon blue light-triggered isomerization of the various lipids back to trans, pinpointing the role of interfacial interactions for the formation of stable Lo lipid raft domains.

Optical Manipulation of Gb3 Enriched Lipid Domains: Impact of Isomerization on Gb3‐Shiga Toxin B Interaction

“…Only if the photo‐Gb 3 partitions into the l o phase in the trans ‐configuration, does the photoisomerization to cis recruit l d phase lipids leading to a re‐organization of the membrane. Our results demonstrate that the complex sugar headgroup of Gb 3 , which is even more complex than a galactose (galactocerebroside) or a phosphocholine group (sphingomyelin) [44] does not interfere with the photoisomerization in the liquid‐liquid phase‐separated membranes. If the azobenzene group is localized at the end of the fatty acid, the trans ‐configuration of the Gb 3 (dark adapted or blue light illumination state) appears to predominantly localize within l o domains, while the cis ‐configuration (UV‐illumination state) induces l d lakes within l o domains thus reorganizing the l o domains and expanding them.…”

Optical Control of Glycerolipids and Sphingolipids

“…These included the optical control of thermal hypersensitivity in vivo via a S1PR3/TRPV1 signaling axis without genetic intervention. [33] 3.3 Sphingomyelin [SM] [35] Sphingomyelin is the most abundant sphingolipid. [28] Like ceramide, sphingomyelin can undergo membrane phase separation.…”

“…A photoswitchable analog of SM, termed AzoSM, enabled optical control of domain formation in supported lipid bilayers. [35] or lipid exchange. [21][22][23] Recent applications by the Lohmüller and Trauner groups include reversible control of lipid organization and fluidity.…”