Fluorophore position of headgroup-labeled Gb glycosphingolipids in lipid bilayers.

Fluorescent lipid probes are an invaluable tool for investigating lipid membranes. In particular, localizing certain receptor lipids such as glycosphingolipids within phase-separated membranes is of pivotal interest to understanding the influence of protein-receptor lipid binding on membrane organization. However, fluorescent labeling can readily alter the phase behavior of a lipid membrane because of the interaction of the fluorescent moiety with the membrane interface.

Differential recognition of lipid domains by two Gb3-binding lectins.

The two lectins LecA from Pseudomonas aeruginosa and the B-subunit of Shiga toxin from Shigella dysenteriae (StxB) share the glycosphingolipid globotriaosylceramide (Gb3) as receptor. Counterintuitively, we found that LecA and StxB segregated into different domains after recognizing Gb3 at the plasma membrane of cells. We hypothesized that the orientation of the carbohydrate head group of Gb3 embedded in the lipid bilayer differentially influences LecA and StxB binding.

Synthesis of Gb Glycosphingolipids with Labeled Head Groups: Distribution in Phase-Separated Giant Unilamellar Vesicles.

The receptor lipid Gb is responsible for the specific internalization of Shiga toxin (STx) into cells. The head group of Gb defines the specificity of STx binding, and the backbone with different fatty acids is expected to influence its localization within membranes impacting membrane organization and protein internalization. To investigate this influence, a set of Gb glycosphingolipids labeled with a BODIPY fluorophore attached to the head group was synthesized.

Shiga toxin binding alters lipid packing and the domain structure of Gb-containing membranes: a solid-state NMR study.

We studied the influence of globotriaosylceramide (Gb3) lipid molecules on the properties of phospholipid membranes composed of a liquid ordered (lo)/liquid disordered (ld) phase separated 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC)/N-palmitoyl-d-erythro-sphingosylphosphorylcholine (PSM)/cholesterol mixture (40/35/20, mol/mol/mol) supplemented with 5 mol% of either short acyl chain palmitoyl-Gb3 or long acyl chain lignoceryl-Gb3 using 2H solid-state NMR spectroscopy. To this end, both globotriaosylceramides were chemically synthesized featuring a perdeuterated lipid acyl chain. The solid-state 2H NMR spectra support the phase separation into a POPC-rich ld phase and a PSM/cholesterol-rich lo phase.

Aldehyde-assisted ruthenium(II)-catalyzed C-H oxygenations.

Versatile ruthenium(II) complexes allow for site-selective C-H oxygenations with weakly-coordinating aldehydes. The challenging C-H functionalizations proceed with high chemoselectivity by rate-determining C-H metalation. The new method features an ample substrate scope, which sets the stage for the step-economical preparation of various bioactive heterocycles.

Glycosylations of cyclopropyl-modified carbohydrates: remarkable β-selectivity using a mannose building block.

A mannosyl donor bearing a spiroannulated cyclopropane unit at C-5 has been prepared, and its behavior in glycosylation reactions investigated. Selectivities in favor of the β-anomer were observed. Corresponding di- and trisaccharides incorporating the rigid cyclopropane motif were assembled.