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

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.

• Authors: Martin Pattky, Simone Nicolardi, Beatrix Santiago-Schübel, Daniel Sydes, Yuri E M van der Burgt, Antonia N Klein, Nan Jiang, Jeannine Mohrlüder, Karen Hänel, Janine Kutzsche, S A Funke, D Willbold, S Willbold, C Huhn
• Journal: Analytical and bioanalytical chemistry (Anal Bioanal Chem) Vol. 407 Issue 22 Pg. 6637-55 (Sep 2015) ISSN: 1618-2650 [Electronic] Germany
• PMID: 26123437 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Peptides
• Sulfates
• Sulfonic Acids

Topics

• Binding Sites
• Electrophoresis, Capillary (methods)
• Hydrophobic and Hydrophilic Interactions
• Peptide Mapping (methods)
• Peptides (chemistry)
• Protein Binding
• Reproducibility of Results
• Sensitivity and Specificity
• Spectrometry, Mass, Electrospray Ionization (methods)
• Spectroscopy, Fourier Transform Infrared (methods)
• Sulfates (chemistry)
• Sulfonic Acids (chemistry)