Labeling Membrane Glycoproteins or Glycolipids with Fluorescent Wheat Germ Agglutinin

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.