Discovered more than a century ago, lectins are a specialized class of plant proteins that bind to specific carbohydrate groups attached to proteins or residing in cell membranes. Today these proteins are commonly utilized in the laboratory to localize glycoproteins and to detect glycol-conjugates in various applications. The lectin known as wheat germ agglutinin selectively binds to N-acetylglucosamine and N-acetylneuraminic (sialic acid) residues. In solution, wheat germ agglutinin exists as a heterodimer that weighs approximately 38,000 Daltons. Some of the many applications for which wheat germ agglutinin has been utilized include nuclear core studies, investigations of plant hemicelluloses, and examinations of intracellular distribution of altered lysosomal proteins. Conjugates of the lectin are also particularly well suited for staining the Golgi network in fixed cells since a number of proteins and lipids found in the Golgi apparatus are glycosylated.

In order to visualize lectin binding to the Golgi complex in MDCK cells, the adherent culture illustrated above was treated with wheat germ agglutinin conjugated to Oregon Green. The cells were subsequently counterstained with Alexa Fluor 568 conjugated to phalloidin to localize the filamentous actin network, and the nucleic acid stain DAPI to label DNA in the nucleus. Images were recorded in grayscale with a QImaging Retiga Fast-EXi camera system coupled to an Olympus BX-51 microscope equipped with bandpass emission fluorescence filter optical blocks provided by Omega Optical. During the processing stage, individual image channels were pseudocolored with RGB values corresponding to each of the fluorophore emission spectral profiles.