MALDI-TOF MS Protein Identification

The detailed procedure for identifying the discriminative peaks using an UltrafleXtreme (Bruker Daltonics, Bremen, Germany) tandem mass spectrometer has been described previously [18 (link)]. Briefly, before the analyses were conducted, the serum samples were purified using ZipTip C18 tips. The obtained eluates (4 µL) were subjected to nanoLC separation, automatically mixed with HCCA matrix solution, and spotted onto an AnchorChip 384 MALDI target plate (Bruker Daltonics, Bremen, Germany). The experiments were performed in the reflectron positive ion mode of the mass spectrometer in the mass range of m/z 700–3500. Protein–peptide identification was based on the SwissProt database and Mascot 2.4.1 search engine. The database searches were taxonomically restricted to Homo sapiens.