Improved Mass Spectrometric Characterization of Protein Glycosylation Reveals Unusual Glycosylation of Maize-Derived Bovine Trypsin

摘要

Although bottom-up proteomics using tryptic digests isnwidely used to locate post-translational modificationsn(PTM) in proteins, there are cases where the protein hasnseveral potential modification sites within a tryptic fragmentnand MS2 strategies fail to pinpoint the location.nWe report here a method using two proteolytic enzymes,ntrypsin and pepsin, in combination followed byntandem mass spectrometric analysis to provide fragmentsnthat allow one to locate the modification sites.nWe used this strategy to find a glycosylation site onnbovine trypsin expressed in maize (TrypZean). Severalnglycans are present, and all are attached to a nonconsensusnN-glycosylation site on the protein.