Characterization of Hydrophilic Post Translational Modifications by LC-MS

Post Translational Modifications (PTM) are modifications which take place following protein biosynthesis. There are hundreds of PTMs which have been discovered and possibly many more which have yet to be discovered. The analysis of the 20 amino acids to study has exponentially increased to seemingly limitless combinations of proteins and PTMs, and this number of possible PTM combinations add daunting challenges for proteomic analysis.

The most diverse PTM, glycosylation, is of great importance leading to the possible bio-markers and biotherapeutics. In 2016, a new protocol was published describing a new technique for releasing Asparagine(N)-linked glycans from a peptide backbone which is much cheaper than standard protocols.¹ Here, the validity of this protocol will be compared to an established technique (PNGase F).²

Another well-studied PTM is the deamidation of Asparagine (Asn) to aspartic acid (Asp) and its isomerization to iso-aspartic acid (i-Asp). The biological consequences of Asn forming i-Asp is a mutagenesis on the secondary structure and conformation of a protein. These consequences demonstrate the importance verifying deamidation and the source of deamidation. Is the deamidation native to the protein, the result of sample preparation, or how the protein had been stored? Here, the sample preparation as a possible source of deamidation is explored.³

1.            Song, X. Z.; Ju, H.; Lasanajak, Y.; Kudelka, M. R.; Smith, D. F.; Cummings, R. D., Oxidative release of natural glycans for functional glycomics. Nature Methods 2016, 13 (6), 528-+.

2.            Fischler DA, Orlando, R. N-linked Glycan Release Efficiency: A Quantitative Comparison between NaOCl and PNGase F Release Protocols. (In Preparation)

3.            Fischler DA, Orlando, R. Deamidation and Isomerization Rates of Asparagine Containing Immunoglobulin G (IgG) Peptides During Trypsin Digestion. (In Preparation)