Thio-triazole-biotin-labeled peptides derived from iPA probes

iPAs are minimal-tag chemical probes - propargyl analogs of putrescine (PUT), spermidine (SPD), and spermine (SPM) - that preserve charge/spacing, retain transporter compatibility, and enable high-resolution intracellular imaging following paraformaldehyde (PFA)-based crosslinking and copper-catalyzed azide-alkyne cycloaddition to a fluorescent reporter. The LC-MS/MS data submitted here support an experiment designed to assess whether intracellular iPAs undergo substantial metabolic/catabolic transformation. MCF-7 cells were treated with iPAs, lysed, and subjected to a copper-catalyzed azide-alkyne-thiol reaction in which solvent-exposed cysteines in proteins react simultaneously with alkyne-bearing probe(s) released from cells and with azide-PEG3-biotin added to the lysis buffer. Proteins were then digested with trypsin; thio-triazole-biotin-labeled peptides were enriched and analyzed by LC–MS/MS. Open-search analysis showed that the observed cysteine mass shifts predominantly correspond to incorporation of the intact, alkyne-retaining probe species. Note that this assay selectively detects alkyne-retaining species and does not quantify potential alkyne-loss products.