Table I Data summary for the identification of protein citrullination in human tissues
Search approachTotal PSMsCit PSMsaC-term CitbBelow identity scorecAmbiguousdValid (MI)Valid peptides (MI)Valid proteins
Database search8,988,14613,0313,9813,0783,8812,091301154
Immonium ion295,83884211410391917
  • a PSMs with Cit annotation at the C-terminus of a tryptic peptide were categorically rejected because trypsin would not generate such a peptide.

  • b PSMs with Mascot ion scores below the identity threshold were discarded to reduce spurious PSMs.

  • c PSMs with otherwise ambiguous spectra, such as incomplete Cit-containing fragment ion series and sequence ambiguities regarding deamindation/citrullination.

  • d PSMs with at least two neutral loss ions from Cit fragment ions in MS2 spectra. MI, manual inspection.