Searches of MS/MS data used a trypsin protease specificity with the possibility of two missed cleavages, a peptide mass tolerance of ±300 ppm, a peptide fragment mass tolerance of ±0.2 Da, and the possibility of carbamidomethylation at cysteine and oxidation at methionine. The tandem MS spectra were validated manually by ensuring the spectra contained at least four consecutive -y or -b ions matching the predicted amino acid sequence.