Tunable Charge Tags for Electron-Based Methods of Peptide Sequencing: Design and Applications

Abstract

Charge tags using basic auxiliary functional groups 6-aminoquinolinylcarboxamido, 4-aminopyrimidyl-1-methylcarboxamido, 2-aminobenzoimidazolyl-1-methylcarboxamido, and the fixedcharge 4-(dimethylamino)pyridyl-1-carboxamido moiety are evaluated as to their properties in electron transfer dissociation mass spectra of arginine C-terminated peptides. The neutral tags have proton affinities that are competitive with those of amino acid residues in peptides. Charge reduction by electron transfer from fluoranthene anion-radicals results in peptide backbone dissociations that improve sequence coverage by providing extensive series of N-terminal ctype fragments without impeding the formation of C-terminal z fragments. Comparison of ETD mass spectra of free and tagged peptides allows one to resolve ambiguities in fragment ion assignment through mass shifts of c ions. Simple chemical procedures are reported for Nterminal tagging of Arg-containing tryptic peptides.

Electron Transfer Reduction of the Diazirine Ring in Gas-Phase Peptide Ions. On the Peculiar Loss of [NH4O] from Photoleucine

“…Other functional groups that work as disruptors have been previously identified (e.g., aromatic amino acid residues furnished with NO 2 or CN substituents [56][57][58], thioxoamide groups [59], or fixed charge tags [60]). Conversely, some side-chain dissociations upon electron capture have been identified on the basis of thermochemical arguments as originating from excited electronic states accessed by electron attachment [61].…”

Gas-Phase Fragmentation of Oligoproline Peptide Ions Lacking Easily Mobilizable Protons

“…Peptides containing 2-(triethylammonium)acetyl and 2-(4-aza-1-azoniabicyclo[2.2.2]octylammonium)acetyl were synthesized according to the procedure described by us previously [14]. The N-terminal amino group of peptides attached to the resin was iodoacetylated for 3 h in the presence of N,N′ -diisopropylcarbodiimide followed by treatment with a 5-fold excess of tertiary amine (Et 3 N and DABCO, respectively) for 24 h at room temperature (Supplementary Data, Figure 1S, procedure A).…”

“…The effect of the arginine residue can be mimicked by peptide derivatization with a fixed positive charge-carrying molecule [13, 14], including quaternary ammonium salts (QAS) [15–18], which enables MS analysis without proton transfer from solvent. In this case, there are three types of hydrogens (α, β and amide) that could undergo intramolecular migration to yield fragment ions.…”

Investigation of the mechanism of electron capture and electron transfer dissociation of peptides with a covalently attached free radical hydrogen atom scavenger

“…Factors influencing the prominent N−C α bond cleavage processes leading to c and z ions in ECD have been a major focus of these investigations. These wide ranging investigations include tagging peptides with permanent charged groups [20–27], electron/hydrogen atom scavengers [28–33] and modified peptide backbones [34–38]. These experiments are primarily designed to monitor the initial electron capture and subsequent electronic state relaxation via internal conversion and intramolecular electron, proton and hydrogen atom transfer processes.…”