Peptide, modified peptide and precursor
In bottom‑up
proteomics peptides are analyzed in a mass spectrometer, usually to infer
information about the proteins they come from. When you analyze your mass
spectrometry results in any of
Biognosys software, you get information for different
elements at different levels, related to the detected peptides (Table 1).
- Peptide (stripped sequence): it refers
to the amino acid sequence regardless of charge state or modification of the
analyzed peptide. It is mainly used for protein inference.
- Modified peptide: it reports
information about the posttranslational modified status of the peptides. In our reports, this appears with the
additional mass added ‑if any‑ to the amino acid residue in square brackets.
- Precursor: this refers to the actual unique molecular unit
being analyzed on the mass spectrometer. It contains information about the
sequence, the modification status, and the charge state. Ultimately, fragment
ions are produced from these precursors.
Following this rational, the number of precursors will always be equal or higher than the number of modified peptides, and the latter equal or higher than the number of stripped sequences (or peptides, Table 1).
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