Abstract
Galectins are a family of glycan binding proteins that stand out for the wide range of biological phenomena in which they are involved. Most galectin functions are associated with their glycan binding capacities, which are generally well characterized at the oligosaccharide level, but not at the glycoprotein or glycolipid level. Glycolipids form the part of cell membranes where they can act as galectin cellular receptors. In this scenario, glycan presentation as well as the membrane chemical and structural features are expected to have a strong impact in these molecular association processes. Herein, liposomes were used as membrane mimicking scaffolds for the presentation of glycosphingolipids (GSLs) and to investigate their interaction with Galectin-3 and the N-domain of Galectin-8 (Gal8N). The binding towards GM3 and GM1 and their non-silaylated GSLs was compared to the binding to the free glycans, devoid of lipid. The analysis was carried out using a combination of NMR methods, membrane perturbation studies, and molecular modeling. Our results showed a different tendency of the two galectins in their binding capacities towards the glycans, depending on whether they were free oligosaccharides or as part of GSL inserted into a lipid bilayer, highlighting the significance of GSL glycan presentation on membranes in lectin binding.
Highlights
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Glycans are presented at cell surfaces attached to either proteins or lipids, where they can be recognized by carbohydrate-binding proteins to mediate or influence diverse processes such as cell adhesion, signaling, intracellular trafficking, or pathogen recognition [1]
The most common presentation of glycans on lipids occurs on a ceramide (Cer) scaffold to generate glycosphingolipids (GSLs)
Summary
The most common presentation of glycans on lipids occurs on a ceramide (Cer) scaffold to generate glycosphingolipids (GSLs). Ceramide structures vary in length, hydroxylation pattern, and degree of saturation of the fatty acid moieties, resulting in lipid structural diversity that impacts the presentation of the attached glycan at the membrane surface [2]. The first sugar linked to Cer can be either Galactose (Gal), or Glucose (Glc), with the latter being typically glycosylated to give lactosylceramide (Galβ1-4GlcβCer, LacCer). This neutral core is the common structure for the ganglio-, lacto-, neolacto-, globo-, and isoglobo- GSL series, as found in mammals
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