Fragmentation of intra-peptide and inter-peptide disulfide bonds of proteolytic peptides by nanoESI collision-induced dissociation |
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Authors: | Michael Mormann Johannes Eble Christian Schwöppe Rolf M Mesters Wolfgang E Berdel Jasna Peter-Katalini? Gottfried Pohlentz |
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Institution: | Institute for Medical Physics und Biophysics, University of Münster, Robert-Koch-Str. 31, 48149, Münster, Germany. |
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Abstract: | Characterisation and identification of disulfide bridges is an important aspect of structural elucidation of proteins. Covalent
cysteine-cysteine contacts within the protein give rise to stabilisation of the native tertiary structure of the molecules.
Bottom-up identification and sequencing of proteins by mass spectrometry most frequently involves reductive cleavage and alkylation
of disulfide links followed by enzymatic digestion. However, when using this approach, information on cysteine-cysteine contacts
within the protein is lost. Mass spectrometric characterisation of peptides containing intra-chain disulfides is a challenging
analytical task, because peptide bonds within the disulfide loop are believed to be resistant to fragmentation. In this contribution
we show recent results on the fragmentation of intra and inter-peptide disulfide bonds of proteolytic peptides by nano electrospray
ionisation collision-induced dissociation (nanoESI CID). Disulfide bridge-containing peptides obtained from proteolytic digests
were submitted to low-energy nanoESI CID using a quadrupole time-of-flight (Q-TOF) instrument as a mass analyser. Fragmentation
of the gaseous peptide ions gave rise to a set of b and y-type fragment ions which enabled derivation of the sequence of the
amino acids located outside the disulfide loop. Surprisingly, careful examination of the fragment-ion spectra of peptide ions
comprising an intramolecular disulfide bridge revealed the presence of low-abundance fragment ions formed by the cleavage
of peptide bonds within the disulfide loop. These fragmentations are preceded by proton-induced asymmetric cleavage of the
disulfide bridge giving rise to a modified cysteine containing a disulfohydryl substituent and a dehydroalanine residue on
the C-S cleavage site. |
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Keywords: | Inter-and intramolecular disulfide bridge Underivatised peptides Low-energy collision-induced dissociation Asymmetric disulfide-bridge cleavage |
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