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Fragmentations of [M–H] – anions of peptides containing Ser sulfate. A joint experimental and theoretical study
Author(s) -
Nha Tran T. T.,
Wang Tianfang,
Hack Sandra,
Bowie John H.
Publication year - 2013
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.6686
Subject(s) - chemistry , sulfate , ion , peptide , crystallography , fragmentation (computing) , mass spectrometry , mass spectrum , analytical chemistry (journal) , stereochemistry , chromatography , organic chemistry , operating system , biochemistry , computer science
RATIONALE To determine the negative‐ion cleavages from [M–H] – ions of Ser sulfate‐containing peptides using experiment and theory in concert. METHODS Fragmentations were explored using a Waters QTOF2 mass spectrometer in negative‐ion electrospray mode, together with calculations at the CAM‐B3LYP/6‐311++g(d,p) level of theory. Peptides used in this study were:GSSO 3 HOH1 GSSO 3 HOCH 31 aGAVSSO 3 HOH2 GAVSSO 3 HOCH 32 aGLSSO 3 H GVA OH3GLSSO 3 H GDA OH4GLSSO 3 H GSSO 3 H A OH5RESULTS Previously, it has been shown that a peptide containing a Tyr sulfate group shows [(M–H) – –SO 3 ] as the base peak. Only a small peak was observed corresponding to HOSO 3 – (formed following rearrangement of the sulfate). A Ser sulfate‐containing peptide, in contrast, shows pronounced peaks due to cleavage product anions [(M–H) – –SO 3 ] and HOSO 3 – . Theoretical calculations at the CAM‐B3LYP/6‐311++g(d,p) level of theory suggest that rearrangement of a Ser sulfate to give C‐terminal CO 2 SO 3 H is energetically unfavourable in comparison with fragmentation of the intact Ser sulfate to yield [(M–H) – –SO 3 ] and HOSO 3 – . [(M–H) – –H 2 SO 4 ] anions are not observed in the spectra of peptides containing Ser sulfate, presumably because HOSO 3 – is a relatively weak gas‐phase base (ΔG acid = 1265 kJ mol –1 ). CONCLUSIONS Experimental and theoretical data suggest that [(M–H) – –SO 3 ] and HOSO 3 – product anions (from a peptide with a C‐terminal Ser sulfate) are formed from the serine sulfate anion accompanied by specific proton transfer. CID MS/MS/MS data for an [(M–H) – –SO 3 ] ion of an underivatised sulfate‐containing peptide will normally allow the determination of the amino acid sequence of that peptide. The one case we have studied where that is not the case is GLS(SO 3 H)GDA(OH), where the peptide contains Ser sulfate and Asp, where the diagnostic Asp cleavages are competitive with the Ser sulfate cleavages. Copyright © 2013 John Wiley & Sons, Ltd.