Interpretation of matrix-assisted laser desorption/ionization postsource decay spectra of charge-derivatized peptides: Some examples of tris[(2,4,6-trimethoxyphenyl) phosphonium]-tagged proteolytic digestion products of phosphoenolpyruvate carboxykinase

Abstract

The fragmentation of peptides, to which a positive charge is attached at the N-terminus, was studied by matrix-assisted laser desorption/ionization postsource decay mass spectrometry. In these experiments, the tris[(2,4,6-trimethoxyphenyl)phosphonium] acetyl group is covalently attached. The main advantage of this modification is that the resulting spectra are simplified and the fragment ions observed consist predominantly of a(n)-type ions. We report the results for charge-derivatized peptides formed following enzymatic digestion of phosphoenolpyruvate carboxykinase. Specific fragmentation of bonds within aspargine and threonine residues are observed and are discussed. The understanding of the mechanistic aspects of the fragmentation process is essential to formulate a simple and straightforward mass spectrometric strategy for peptide sequencing using these charged derivatives.

Photodissociation of Charge Tagged Peptides

“…The TMPP ion (m/z 573. 19) dominates the PSD spectrum (Figure 3c) with some sequence ions just above noise level. Photodissociation (Figure 3d) produces more intense sequence ions and an almost complete series of a n ions.…”

“…However, this kind of charge sequestering is not absolute and a proton can still move around to some extent. To address these problems, several types of peptide derivatization schemes have been developed in the past 20 years [14][15][16][17][18][19][20][21]. Charge tags, based on phosphonium or quaternary ammonium ions, may be helpful in improving sensitivity for detecting peptides that may not readily ionize.…”

“…It does not decompose to produce a mobile proton like TMAB. Several studies demonstrated that the phosphonium ion is absolutely fixed at the Nterminus, and N-terminal a n ions are produced [16][17][18][19]29]. Recent studies also indicate that the fragmentation efficiency of arginine-containing charge-tagged peptides is low [20,28,30].…”

Electron-Capture and -Transfer Dissociation of Peptides Tagged with Tunable Fixed-Charge Groups: Structures and Dissociation Energetics

“…However, a more general approach is to derivatize in situ the desired peptide with a charge-carrying or readily ionizable group [17][18][19][20][21][22][23][24], and thus affix the charge position in the sequence. Various charge tags have been implemented on an ad hoc basis of availability and convenience, such as 2,4,6-trimethylpyridinium [25], 2,2′-bipyridyl [26], tris (2,4,6-trimethoxyphenyl)phosphonium [24,[27][28][29], trimethylammoniumalkyl [30], etc. The charge tags function as potential electron attachment sites, depending on their intrinsic recombination energies (REs) relative to those of the charged peptide residue [31].…”

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

“…Several charge tags have been investigated on the basis of their chemical availability or synthetic convenience, e.g., 2,4,6-trimethylpyridinium [4], 2,2'-bipyridyl [5], tris(2,4,6-trimethoxyphenyl)phosphonium (TMPP) [6][7][8], and trimethylammoniumalkyl [9,10]. Enhanced charging can also be achieved by introducing into the peptide the basic guanidine group by various guanidination strategies [11][12][13][14][15][16][17].…”