*2.3.2 LC-ESI-Q-IT MS*

The tryptic peptide mixture was purified with ZipTipC18, and analyzed with LC-ESI-Q-IT MS on an LCQDeca mass spectrometer (Thermo Finnigan, San Jose, CA, USA). The MS/MS data were obtained to search Swiss-Prot database for protein identification. The detailed procedure was described previously [22].
