The Shiga toxin B subunit (STxB), which is involved in cell membrane attachment and trafficking of Shiga holotoxin, binds specifically to the glycosphingolipid Gb 3. In biological membranes, Gb 3 glycosphingolipids differ in their fatty acid composition and there is strong evidence that the fatty acid alters the binding behaviour of STxB as well as the intracellular routing of the Shiga toxin/Gb 3 complex. To analyse the binding of STxB to different Gb 3 s, we chemically synthesized saturated, unsaturated, a-hydroxylated Gb 3 s and a combination thereof, all based on a C 24-fatty acid chain starting from monosaccharide building blocks, sphingosine and the respective fatty acids. These chemically well-defined Gb 3 s were inserted into solid supported phase-separated lipid bilayers composed of DOPC/sphingomyelin/cholesterol as a simple mimetic of the outer leaflet of animal cell membranes. By fluorescenceand atomic force microscopy the phase behaviour of the bilayer as well as the lateral organization of bound STxB were analysed. The fatty acid of Gb 3 significantly alters the ratio between the ordered and disordered phase and induces a third intermediate phase in the presence of unsaturated Gb 3. The lateral organization of STxB on the membranes varies significantly. While STxB attached to membranes with Gb 3 s with saturated fatty acids forms protein clusters, it is more homogeneously bound to membranes containing unsaturated Gb 3 s. Large interphase lipid redistribution is observed for a-hydroxylated Gb 3 doped membranes. Our results clearly demonstrate that the fatty acid of Gb 3 strongly influences the lateral organization of STxB on the membrane and impacts the overall membrane organization of phase-separated lipid membranes.

A versatile and rapid access to various chain lengths of ethylene-bridged BODIPY motifs was discovered. Corresponding oligomers comprising up to eight monomeric units were studied with respect to their microstructures by photophysical, X-ray crystallographic, and computational means. The investigation of three different dipyrrin cores revealed a crucial dependence on the substitution pattern of the core, whereas the nature of the meso-periphery is less critical. The impact of substituent effects on the conformational space was investigated by Monte Carlo simulations and a set of DFT methods (B3LYP, PBEh-3c, TPSS/PWPB95), including dispersion effects. Cryptopyrrole-derived oligo-BODIPYs are characterized by a tight intramolecular arrangement triggering a dominant J-type excitonic coupling with red-shifts up to 45 nm, exceptionally small line widths of the absorption and emission event (up to 286 cm), outstandingly high attenuation coefficients (up to 1 042 000 M cm), and quantum yields of up to unity.

Shiga toxin subunit B (STxB) binding to its cellular receptor Gb3 leads to the formation of protein-lipid clusters and bending of the membrane. A newly developed synthetic route allowed synthesizing the biologically most relevant Gb3-C24:1 2OH species with both, the natural (Gb3-R) as well as the unnatural (Gb3-S) configuration of the 2OH group. The derivatives bind STxB with identical nanomolar affinity, while the propensity to induce membrane tubules in giant unilamellar vesicles is more pronounced for Gb3-S. Fluorescence and atomic force microscopy images of phase-separated supported membranes revealed differences in the lateral organization of the protein on the membrane. Gb3-R favorably induces large and tightly packed protein clusters, while a lower protein density is found on Gb3-S doped membranes.

A fundamental, highly fluorescent, and easily accessible scaffold derived from the BODIPY core is reported. The use of benzimidazole as a bridging ligand at the meso position enables the binding of two BF units to provide sufficient rigidity and enhanced electron-withdrawing strength. Absorption and emission events thus take place in the red (λ≈600 nm); the fluorescence quantum yields can reach unity (0.96) and show little dependence on solvent polarity. The synthetic route was shortened to two steps starting from commercially available precursors while the preparation is modular and tolerates various pyrrole and benzimidazole moieties. Fluoride replacement by propynyl groups, various halogenations, as well as Knoevenagel-type condensations were applied to extend the versatility of these new photostable fluorophores, which we termed BOIMPYs.