Labeling Membrane Glycoproteins or Glycolipids with Fluorescent Wheat Germ Agglutinin

INTRODUCTION: Glycoprotein and glycolipids are found as part of the outer leaflet of cellular plasma membranes. Those glycoproteins or glycolipids that contain sialic acid and N-acetylglucosamine residues can be labeled with wheat germ agglutinin (WGA), a plant lectin that exists as a dimer (mwt ~36,000) and is normally cationic. Fluorescently labeled WGA is commercially available with fluorescein, Alexa Fluor, or rhodamine moieties. Fluorescent WGA can also be used to stain the Golgi (the trans-Golgi) in fixed cells. Fluorescently labeled concanavalin A (Con A), which selectively binds to α-mannopyranosyl and α-glucopyranosyl residues, can also be used to label plasma membranes. This protocol describes the labeling of membrane glycoproteins or glycolipids with fluorescent WGA.