Peptide-Spectrum Match is the most fundamental unit of data in bottom-up proteomics, representing the moment a specific mass spectrum is successfully linked to a specific peptide sequence.
Conceptually, PSMs are similar to reads in RNA-seq. In both fields, these units represent the “raw counts” generated by a high-throughput machine—a mass spectrometer for proteins and a sequencer for RNA. Just as a “read” is a digitized sequence of nucleotides representing a fragment of an RNA molecule, a PSM is a digitized identification of a peptide fragment from a protein. In both workflows, the goal is to map these small, fragmented pieces back to a reference “map,” whether that is a genome for RNA-seq or a protein database for proteomics, to determine what was present in the original sample.
The table below compares the difference between them
