Structure characterization of unexpected covalent O-sulfonation and ion-pairing on an extremely hydrophilic peptide with CE-MS and FT-ICR-MS

Pattky, Martin; Willbold, S.; Willbold, D.; Klein, Antonia N.; Nicolardi, Simone; Jiang, Nan; Huhn, C.; Kutzsche, Janine; Funke, S. A.; van der Burgt, Yuri E. M.; Hänel, Karen; Sydes, Daniel; Mohrlüder, Jeannine; Santiago-Schübel, Beatrix

doi:10.1007/s00216-015-8826-8

Journal Article

FZJ-2015-06891

Structure characterization of unexpected covalent O-sulfonation and ion-pairing on an extremely hydrophilic peptide with CE-MS and FT-ICR-MS

Pattky, M. ; Nicolardi, S. ; Santiago-Schübel, B.FZJ* ; Sydes, D. ; van der Burgt, Y. E. M. ; Klein, A. N.FZJ* ; Jiang, N.FZJ* ; Mohrlüder, J.FZJ* ; Hänel, K.FZJ* ; Kutzsche, J.FZJ* ; Funke, S. A. ; Willbold, D.FZJ* ; Willbold, S.FZJ* ; Huhn, C. (Corresponding author)

2015
Springer Berlin

Analytical and bioanalytical chemistry 407(22), 6637 - 6655 (2015) [10.1007/s00216-015-8826-8]

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Please use a persistent id in citations: doi:10.1007/s00216-015-8826-8

Abstract: In this study, we characterized unexpected side-products in a commercially synthesized peptide with the sequence RPRTRLHTHRNR. This so-called peptide D3 was selected by mirror phage display against low molecular weight amyloid-β-peptide (Aβ) associated with Alzheimer’s disease. Capillary electrophoresis (CE) was the method of choice for structure analysis because the extreme hydrophilicity of the peptide did not allow reversed-phase liquid chromatography (RPLC) and hydrophilic interaction stationary phases (HILIC). CE-MS analysis, applying a strongly acidic background electrolyte and different statically adsorbed capillary coatings, provided fast and efficient analysis and revealed that D3 unexpectedly showed strong ion-pairing with sulfuric acid. Moreover, covalent O-sulfonation at one or two threonine residues was identified as a result of a side reaction during peptide synthesis, and deamidation was found at either the asparagine residue or at the C-terminus. In total, more than 10 different species with different m/z values were observed. Tandem-MS analysis with collision induced dissociation (CID) using a CE-quadrupole-time-of-flight (QTOF) setup predominantly resulted in sulfate losses and did not yield any further characteristic fragment ions at high collision energies. Therefore, direct infusion Fourier transform ion cyclotron resonance (FT-ICR) MS was employed to identify the covalent modification and discriminate O-sulfonation from possible O-phosphorylation by using an accurate mass analysis. Electron transfer dissociation (ETD) was used for the identification of the threonine O-sulfation sites. In this work, it is shown that the combination of CE-MS and FT-ICR-MS with ETD fragmentation was essential for the full characterization of this extremely basic peptide with labile modifications.

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