Chemically synthesized Gb 3 glycosphingolipids: tools to access their function in lipid membranes
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REVIEW
Chemically synthesized Gb3 glycosphingolipids: tools to access their function in lipid membranes Jeremias Sibold1 · Somayeh Ahadi2 · Daniel B. Werz2 · Claudia Steinem1,3 Received: 29 June 2020 / Revised: 24 August 2020 / Accepted: 26 August 2020 © The Author(s) 2020
Abstract Gb3 glycosphingolipids are the specific receptors for bacterial Shiga toxin. Whereas the trisaccharidic head group of G b3 defines the specificity of Shiga toxin binding, the lipophilic part composed of sphingosine and different fatty acids is suggested to determine its localization within membranes impacting membrane organisation and protein binding eventually leading to protein internalisation. While most studies use G b3 extracts, chemical synthesis provides a unique tool to access different tailor-made G b3 glycosphingolipids. In this review, strategies to synthesize these complex glycosphingolipids are presented. Special emphasis is put on the preparation of Gb3 molecules differing only in their fatty acid part (saturated, unsaturated, α-hydroxylated and both, unsaturated and α-hydroxylated). With these molecules in hand, it became possible to investigate the phase behaviour of liquid ordered/liquid disordered supported membranes doped with the Gb3 species by means of fluorescence and atomic force microscopy. The results clearly highlight the influence of the different fatty acids of the G b3 sphingolipids on the phase behaviour and the binding properties of Shiga toxin B subunits, even though the membranes were only doped with 5 mol% of the receptor lipid. To obtain fluorescent G b3 derivatives, either fatty acid labelled Gb3 molecules or head group labelled ones were synthesized. These molecules enabled us to address the question, where the Gb3 sphingolipids are localized prior protein binding by means of fluorescence microscopy on giant unilamellar vesicles. The results again demonstrate that the fatty acid of Gb3 plays a pivotal role for the overall membrane organisation. Keywords Fluorescence microscopy · Glycolipids · Model membranes · Organic synthesis · Shiga toxin
Introduction Glycosphingolipids Glycosphingolipids (GSLs) are a subclass of glycolipids that are found in cell membranes of various organisms ranging Special Issue: Multicomponent lipid membranes. * Daniel B. Werz d.werz@tu‑braunschweig.de * Claudia Steinem [email protected]‑goettingen.de 1
Georg‑August‑Universität Göttingen, Institute of Organic and Biomolecular Chemistry, Tammannstr. 2, 37077 Göttingen, Germany
2
Technische Universität Braunschweig, Institute of Organic Chemistry, Hagenring 30, 38106 Braunschweig, Germany
3
Max Planck Institute for Dynamics and Self Organization, Am Faßberg 17, 37077 Göttingen, Germany
from bacteria to humans. Being typically a minor component of the cell membrane, they are of utmost importance for biological functions that rely on lipid-lipid and lipid-protein interactions (Schnaar and Kinoshita 2015). The chemical structure of 90% of mammalian GSLs is based on glucosyl ceramide, w
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