Association of Glycolipids and Growth Factor Receptors in Lipid Rafts

Glycolipids improve the stability of liposomes: The perspective of bilayer membrane structure

The storage and thermal stability of liposomes, which are amphiphilic carriers, cause very large challenges. However, glycolipid modification may be a potential method to improve the stability of liposomes. In this study, the mechanism by which tilapia head glycolipids improve the stability of liposomes was studied. The head groups of glycolipids and liposomes have a strong interaction (K_a = 633.650 M^-1), mainly due to hydrogen bonds, which promote the formation of microstructure domains between glycolipids and liposomes. In addition, glycolipids caused the bilayer structure of liposomes to rearrange, resulting in an increase in the phase transition temperature, tight arrangement of membrane molecules, and increase in membrane thickness (from 2.4 nm to 3.5 nm). Novelty, the formation of microstructure domains helped prevent the liposomes membrane structure from being disrupted during storage and heat. Therefore, glycolipid modification improved the stability of liposomes. This study can provide new insights into the development of high-stability liposomes.

Oligosaccharide Presentation Modulates the Molecular Recognition of Glycolipids by Galectins on Membrane Surfaces

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.

Membrane Domain Localization and Interaction of the Prion-Family Proteins, Prion and Shadoo with Calnexin

The cellular prion protein (PrP^C) is renowned for its infectious conformational isoform PrP^Sc, capable of templating subsequent conversions of healthy PrP^Cs and thus triggering the group of incurable diseases known as transmissible spongiform encephalopathies. Besides this mechanism not being fully uncovered, the protein’s physiological role is also elusive. PrP^C and its newest, less understood paralog Shadoo are glycosylphosphatidylinositol-anchored proteins highly expressed in the central nervous system. While they share some attributes and neuroprotective actions, opposing roles have also been reported for the two; however, the amount of data about their exact functions is lacking. Protein–protein interactions and membrane microdomain localizations are key determinants of protein function. Accurate identification of these functions for a membrane protein, however, can become biased due to interactions occurring during sample processing. To avoid such artifacts, we apply a non-detergent-based membrane-fractionation approach to study the prion protein and Shadoo. We show that the two proteins occupy similarly raft and non-raft membrane fractions when expressed in N2a cells and that both proteins pull down the chaperone calnexin in both rafts and non-rafts. These indicate their possible binding to calnexin in both types of membrane domains, which might be a necessary requisite to aid the inherently unstable native conformation during their lifetime.