Updated publication reference for PubMed record(s): 32807795. The aim of the proteomics experiment was to determine the specificity of the generated monobodies for the target protein STAT3. This was done in an affinity-enrichment experiment using two endogenously expressed and tandem-affinity-tagged monobodies in two different cell lines (Jurkat and K562). Eluted proteins after affinity purification were resolved by SDS-PAGE, and analysed using bottom-up proteomics workflow including tryptic digestion, LC-MS/MS, database-search and spectral counting.