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In Situ Imaging of N‐Glycans by MALDI Imaging Mass Spectrometry of Fresh or Formalin‐Fixed Paraffin‐Embedded Tissue

Glycosylation of cell surface, secreted, and circulating proteins is one of the most common types of post‐translational modification. These modifications occur most commonly as one of three major classes: N‐linked glycosylation on asparagine residues, O‐linked glycosylation on serine or threonine residues, or as glycosaminoglycan oligosaccharide polymers on serine. Specifically, for N‐linked glycans, an endoglycosidase enzyme, peptide N‐glycosidase F (PNGase F), cleaves the attached oligosaccharides between the asparagine and first sugar. A method to analyze released N‐glycans and map them to specific locations within a tissue is presented here. The PNGase F is applied by solvent sprayer as a molecular layer on frozen or formalin‐fixed tissues and all released N‐glycans in a given region of tissue are detected using matrix‐assisted laser desorption/ionization (MALDI) imaging mass spectrometry (MALDI‐IMS). Using the described MALDI‐IMS protocol, at least 40 or more individual N‐glycans can be mapped to tissue histopathology and extracted for further structural analysis approaches. © 2018 by John Wiley & Sons, Inc.