Electron cryo-microscopy studies of protein-carbohydrate complexes and glycoproteins

Abstract

The recent resolution revolution experienced by electron cryo-microscopy (Cryo-EM) has meant the technique has begun to displace X-ray crystallography (XRD) as the method of choice for elucidating the structure of large complexes and, more recently, single proteins. While most of the advances that have pushed the technique's resolution and size limits have been made using highest-end 300 keV instrumentation, it should be possible to complete complex structural biology projects with more accessible hardware. One particular area of interest and of inherent complexity is structural glycobiology: glycoproteins and protein-carbohydrate complexes have traditionally been affected by shortfalls in methodology and the intrinsic difficulties associated with the mobility of oligosaccharide chains. Recent studies comparing the quality of carbohydrate structure derived by XRD and Cryo-EM have demonstrated differences, which might be attributable to the nature of the experiments. In this work, we aim to further test these differences using an enzyme-ligand complex (beta-galactosidase with 4-epi cyclophellitol) and a small glycoprotein (human transferrin), using a middle-range 200 keV electron cryo-microscope (TFS Glacios).