on 08-23-201205:33 AM - edited on 10-15-202111:13 AM by Closed Account
Zhang H, Huang RY, Jalili PR, Irungu JW, Nicol GR, Ray KB, Rohrs HW, Gross ML. Anal Chem. 2010 Dec 15;82(24):10095-101. Although bottom-up proteomics using tryptic digests is widely used to locate post-translational modifications (PTM) in proteins, there are cases where the protein has several potential modification sites within a tryptic fragment and MS(2) strategies fail to pinpoint the location. We report here a method using two proteolytic enzymes, trypsin and pepsin, in combination followed by tandem mass spectrometric analysis to provide fragments that allow one to locate the modification sites. We used this strategy to find a glycosylation site on bovine trypsin expressed in maize (TrypZean). Several glycans are present, and all are attached to a nonconsensus N-glycosylation site on the protein.