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Deamidation reactions of protonated asparagine and glutamine investigated by ion spectroscopy
Author(s) -
Kempkes Lisanne J. M.,
Martens Jonathan K.,
Grzetic Josipa,
Berden Giel,
Oomens Jos
Publication year - 2016
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.7464
Subject(s) - chemistry , deamidation , protonation , infrared spectroscopy , dissociation (chemistry) , tandem mass spectrometry , spectroscopy , asparagine , infrared multiphoton dissociation , mass spectrometry , ion , photochemistry , crystallography , amino acid , organic chemistry , chromatography , biochemistry , physics , quantum mechanics , enzyme
Rationale Deamidation of Asn and Gln residues is a primary route for spontaneous post‐translational protein modification. Several structures have been proposed for the deamidation products of the protonated amino acids. Here we verify these structures by ion spectroscopy, as well as the structures of parallel and sequential fragmentation products. Methods Infrared ion spectroscopy using the free electron laser FELIX has been applied to the reaction products from deamidation of protonated glutamine and asparagine in a tandem mass spectrometer. IR spectra were recorded over the 800–1900 cm −1 spectral range by infrared multiple‐photon dissociation (IRMPD) spectroscopy. Molecular structures of the fragment ions are derived from comparison of the experimental spectra with spectra predicted for different candidate structures by density functional theory (DFT) calculations. Results [AsnH + – NH 3 ] + is found to possess a 3‐aminosuccinic anhydride structure protonated on the amino group. The dissociation reaction involving loss of H 2 O and CO forms a linear immonium ion. For [GlnH + –NH 3 ] + , the N‐terminal nitrogen acts as the nucleophile leading to an oxo‐proline product ion structure. For [GlnH + –NH 3 ] + , a sequential loss of [CO + H 2 O] is found, leading to a pyrolidone‐like structure. We also confirm by IR spectroscopy that dehydration of protonated aspartic acid (AspH + ) and glutamic acid (GluH + ) leads to identical structures as to those found for the loss of NH 3 from AsnH + and GlnH + . Conclusions The structure determined for AsnH + is in agreement with the suggested structure derived from measured and computed activation energies. IR ion spectra for the NH 3 ‐loss product from GlnH + establish that a different reaction mechanism occurs for this species as compared to AsnH + . For both amino acids, loss of NH 3 occurs from the side chain. Copyright © 2016 John Wiley & Sons, Ltd.