3B-O1-0940 PDF
Distinguish C-Terminal Side Ions in MALDI In-Source Decay Spectrum by Pseudo-MS3
Matrix-assisted laser desorption/ionization in-source decay (MALDI-ISD) is a useful method for top-down sequencing of proteins and preferentially produces the c'/z• fragment pair. Subsequently, radical z• fragments undergo a variety of radical reactions. This article focuses on the chemical properties of the 1,5-diaminonaphthalene (1,5-DAN) adduct on z fragment ions (zn*), which are abundant ions in MALDI-ISD spectra. Post-source decay (PSD) of the zn* fragments resulted in specific peptide bond cleavage adjacent to the binding site of 1,5-DAN, leading to the preferential formation of y'(n–1) fragments. The dominant loss of an amino acid with 1,5-DAN from zn* can be used in pseudo-MS3 mode to identify the C-terminal side fragments from a complex MALDI-ISD spectrum or to determine missed cleavage residues using MALDI-ISD. Although the N–Cα bond at the N-terminal side of Pro is not cleaved by MALDI-ISD, pseudo-MS3 via zn* can confirm the presence of a Pro residue.