Detection of glycoproteins separated by nondenaturing polyacrylamide gel electrophoresis using the periodic acid-Schiff stain

We observed that published methods for staining glycoproteins in sodium dodecyl sulfate-polyacrylamide gels did not stain glycoproteins separated by nondenaturing polyacrylamide gel electrophoresis. Therefore, the periodic acid-Schiff stain for glycoprotein was adapted for use with proteins analyzed by nondenaturing polyacrylamide gel electrophoresis. Following nondenaturing polyacrylamide gel electrophoresis proteins were denatured in situ by incubation with aqueous 2% sodium dodecyl sulfate, 5% 2-mercaptoethanol, 40% ethanol, and 5% acetic acid at 90°C for 15 min followed by periodic acid-Schiff staining. This modified procedure will detect at least 0.2 μg protein-associated carbohydrate. Omission of the periodic acid treatment from the protocol was used as a control to detect nonspecific staining of some proteins. This modified procedure was validated using both purified glycoproteins and extracellular culture fluid containing carbohydrate-associated proteins of Ruminococcus flavefaciens.