Fluorescent glycan fingerprinting of SARS2 spike proteins

Glycosylation is the most common post-translational modification and has myriad of biological functions. However, glycan analysis has always been a challenge. Here, we would like to present new techniques for glycan fingerprinting based on enzymatic fluorescent labeling and gel electrophoresis. The method is illustrated on SARS2 spike (S) glycoproteins. SARS2, a novel coronavirus and the causative agent of the COVID-19 pandemic, has had significant social and economic impacts since the end of 2019. To obtain the N-glycan fingerprint of an S protein, glycans released from the protein are first labeled through enzymatic incorporation of fluorophore-conjugated sialic acid or fucose, then separated by SDS-PAGE, and finally visualized with a fluorescent imager. To identify the labeled glycans of a fingerprint, glycan standards and glycan ladders are enzymatically generated and run alongside the samples as references. By comparing the mobility of a labeled glycan to that of a glycan standard, the identity of glycans maybe determined. O-glycans can also be fingerprinted. Due to the lack of an enzyme for broad O-glycan release, O-glycans on the S protein can be labeled with fluorescent sialic acid and digested with trypsin to obtain labeled glycan peptides that are then separated by gel electrophoresis. Glycan fingerprinting could serve as a quick method for globally assessing the glycosylation of a specific glycoprotein.