Comprehensive Phosphorylation Site Analysis of α-S2 Casein Using Microwave-Assisted Acid Hydrolysis and Phosphopeptide Enrichment

摘要

In this work MAAH digestion was used to generate a large number of peptides by non-specific cleavages. 8 out of 12 phosphorylation sites were isolated in single peptides, allowing unambiguous site assignment. No peptides were found to contain S56-S58, despite runs that also used an inclusion list. However, these missing peptides were found using MALDI and trypsin digestion. This work shows the strength of MAAH to pinpoint modification sites without ambiguity, and shows the need to use complementary techniques such as QTOF, Orbitrap, and MALDI-TOF/TOF to gain a clear picture of variable modification sites. As a result of these techniques, it was found that most of the phosphorylation sites in α-S2 casein are variably modified.