Liquid chromatography with tandem mass spectrometry analysis. The tryptic peptides were dissolved in 0.1% formic acid (solvent A), directly loaded onto a home-made reverse-phase analytical column (15-cm length, 75 μm inner diameter.). The gradient was increased from 6% to 23% solvent B (0.1% formic acid in 98% acetonitrile) over 16min, then 23% to 35% for 8min and was increased to 80% for 3min, then held at 80% for the last 3min, all at a constant flow rate of 400nl min−1 on an EASY-nLC 1000 UPLC system. The peptides were applied to a nanospray ion source followed by tandem mass spectrometry (MS/MS) in a Q Exactive Plus system (Thermo Fisher Scientific) coupled online to the ultra-performance liquid chromatography system. The electrospray voltage applied was 2.0 kV. The m/z scan range was 350 to 1800 for a full scan, and intact peptides were detected in an Orbitrap mass analyzer at a resolution of 70,000. Peptides were then selected for MS/MS using a normalized collision energy setting of 28 and thefragments were detected in the Orbitrap at a resolution of 17,500. A data-dependent procedure that alternated between one MS scan followed by 20 MS/MS scans with 15.0 s dynamic exclusion was carried out. The automatic gaincontrol was set at 5E4.