Direct Visualization of Galectin-Glycan Lattice using Cryo-Electron Microscopy (cryo-EM) Techniques

Carlos Manuel Alberto Guardia

National Cancer Institute

By binding to specific glycans on plasmalemmal glycoproteins, oligomeric glycan-binding proteins (lectins) help to organize glycoprotein assemblies on the surface of the cell. These lectin-glycoprotein lattices are characterized by multiple low-affinity interactions, and the strength of the interactions can be dynamically modulated by altering protein glycosylation or lectin expression. One family of multivalent lectins that can organize cell-surface microdomains or lattices is the galectins. So far, the formation of these lattices has only been shown indirectly in the formation of structural aggregates on the surface of cells. We are interested in studying the formation of these lattices with a higher degree of detail: a direct visualization, using a sub-nano scale resolution approach, would conclusively demonstrate the formation of these galectin-glycan-receptors networks and the dependence of the structure of the protein to carry out the formation of them. In the field of structural biology, it is known that cryo-electron microscopy (cryo-EM) techniques are a powerful tool to monitor protein structural changes in their native biological environments (without fixing or stain in any way the sample). The aim of this project is to demonstrate the existence and study the galectin-glycan lattices in the surface of the cell by cryo-electron microscopy techniques. We expect that these results would allow us to obtain the first images of a lattice in the surface of the cells, determine in situ the nature of the interactions that leads to the formation and maintenance the structure, and the final importance of these complexes in the activation of the glycosilated receptors through complementary cell biology experiments.