Arabidopsis cell LC-MSMS - Proteomics analysis reveals a highly heterogeneous proteasome composition and the post-translational regulation of peptidase activity under pathogen signaling in plants

26S proteasome was affinity-purified with anti-FLAG beads and separated by 2-DE method. Each spot was cut and digested by Trypsin enzyme, which finaly applied for LC-MS/MS nalysis using a LTQ-Orbitrap XL (Thermo Scientific). The obtained spectra were compared against 35,386 sequences in The Arabidopsis Information Resource 10 (TAIR10; http://www.arabidopsis.org/) using the MASCOT server (version 2.4; Matrix Science) with the following search parameters: threshold set-off at 0.05 in the ion-score cut-off; protein identification cut-off set to two assigned spectra per predicted protein; peptide tolerance at 10 ppm; MS/MS tolerance at +/- 0.5 Da; peptide charge of 2+ or 3+; trypsin as the enzyme and allowing up to one missed cleavage; carboxymethylation on cysteines as a fixed modification and oxidation on methionine as a variable modification.