Wheat germ agglutinin

[5] N-acetyl-D-glucosamine in the natural environment of wheat is found in the chitin of insects, and the cell membrane of yeast & bacteria.

In those animals sialic acid is found in mucous membranes, e.g. the lining of the inner nose, and digestive tract.

[5] Since WGA binds to glycoconjugates, it can be used to label cell membranes,[8] fibrotic scar tissue[9] and arbuscular mycorrhizae[10] for imaging and analysis.

[11] WGA has also demonstrated some cytotoxicity and has thus been used in recent research involving hematological cancers, particularly acute myeloid leukemia.

[2] In addition, WGA has been thought to improve drug delivery due to its ability to cross the blood-brain barrier, but research has yet to be performed on this hypothesis.

The above image shows WGA3 in the program Chimera (PDB code 1WGT). The cyan color shows the cysteine residues, the light green color shows the glycine residues, and the dark gray color shows the remaining hydrophobic residues.
A fluorescent microscopy image of a fungal arbuscule stained with WGA and Alexa Fluor