N-Terminal Derivatization of Peptides with 4'-Formylbenzo-18-crown-6-ether for Protein and Species Identification

Our research objective was to investigate the use of 4’-formylbenzo-18-crown-6-ether (4fb18C6) for the covalent labelling of peptides for unambiguous peptide identification. Specifically, 23 peptides were analysed using a coupled system of liquid chromatography and tandem mass spectrometry with electrospray ionization to test de novo sequencing of derivatized and intact peptides. The reaction was optimized for reductive amination to be performed in an aqueous medium at pH 6 using the microwave radiation. After matching the tandem mass spectra of derivatized and intact peptides in the range of ±0.005 Da, the chemical noise was reduced by up to 90 % and six proteins from 17 different species were identified using the BLASTp algorithm (NCBInr and UniProtKB/Swiss-Prot databases). Species identification enabled further accelerated database search using the classical method of mass spectra database matching. The presented method enables reliable de novo sequencing of peptides and represents a new tool for species identification.