Selective Screening of Tyrosine-Nitrated Peptides in Tryptic Mixtures by In-Source Photodissociation at 355 nm in Matrix-Assisted Laser Desorption Ionization

摘要

ABSTRACT: Nitration of tyrosine residues in proteins is an important post-translationalnmodification related to various diseases such as Alzheimer’s. In this work, efficient andnselective photodissociation (PD) at 355 nm was observed for [M þ H]nþ,[M þ H -n16]nþ, and [M þ H - 32]nþ generated by matrix-assisted ultraviolet laser desorptionnionization (UV-MALDI) of tyrosine-nitrated peptides (nitropeptides). Product ionnspectra obtained by post-source PD at this wavelength contained useful information onnthe amino acid sequence. The spectra for nitropeptides obtained with 355 nmnirradiation inside the ion source (MALDI/in-source PD) displayed characteristic tripletnpatterns due to PD of the above ions. For peptides displaying prominent signal in anMALDI mass map of a tryptic mixture, which are mostly those with arginine at thenC-terminus, in-source PD allowed positive identification of their tyrosine-nitrated forms. Identification of such nitropeptides wasnpossible at the 10 fmol level (in tryptic digest of 100 fmol BSA).