Dehydration reactions of protonated dipeptides containing asparagine or glutamine investigated by infrared ion spectroscopy

Abstract

The role of specific amino acid side-chains in the fragmentation chemistry of gaseous protonated peptides resulting from collisional activation remains incompletely understood. For small peptides containing asparagine and glutamine, a dominant fragmentation channel induced by collisional activations is, in addition to deamidation, the loss of neutral water. Identifying the product ion structures from H2O-loss from four protonated dipeptides containing Asn or Gln using infrared ion spectroscopy, mechanistic details of the dissociation reactions are revealed. Several sequential dissociation reactions have also been investigated and provide additional insights into the fragmentation chemistry. While water loss can in principle occur from the C-terminus, the side chain or the amide bond carbonyl oxygen, in most cases the C-terminus was found to detach H2O, leading to a b2-sequence ion with an oxazolone structure for AlaGln, and bifurcating mechanisms leading to both oxazolone and diketopiperazine species for AlaAsn and AsnAla. In contrast, GlnAla expels water from the amide side chain leading to an imino-substituted prolinyl structure.

Water Loss from Protonated XxxSer and XxxThr Dipeptides Gives Oxazoline—Not Oxazolone—Product Ions

“…If correct, this observation parallels a bifurcating dehydration mechanism previously observed for protonated AsnAla, where H 2 O expulsion from the C-terminus forms isomeric oxazolone and diketopiperazine product ions. 49 …”

“…Our group recently investigated dehydration pathways of protonated dipeptides containing Asn and Gln. 49 Whereas AlaAsn and AsnAla follow a bifurcating mechanism leading to oxazolone as well as diketopiperazine product ions, AlaGln exclusively produced oxazolone fragments. In contrast, for GlnAla, expulsion of water mainly occurs from the Gln side-chain, resulting in a five-membered imino-substituted prolinyl structure, in line with earlier studies on the dehydration and deamidation of peptides with an N-terminal Gln or Glu residue.…”

Investigation of the position of the radical in z3-ions resulting from electron transfer dissociation using infrared ion spectroscopy

“…No apparent differences were noticed in the wavelengthdependent fragmentation into the individual dissociation channels; no clear evidence was therefore found for the co-existence of multiple isomers, such as for instance in some of our previous CID MS/MS studies. 77,78 The yield is linearly corrected for the frequency-dependent change in the laser pulse energy and the infrared frequency is calibrated using a grating spectrometer (FELIX) or a wavemeter (OPO).…”

Experimental and computational studies of monovalent metal cation–peptide interactions in [M·GlyGlyHis]+ (M = Li, Na, K, Rb, Cs, and Ag) complexes

“…Structures and dissociation behavior of metal cationpeptide complexes have been studied extensively for many years through spectroscopy [1][2][3][4][5][6][7][8][9] and tandem mass spectrometry. [10][11][12][13][14][15][16][17][18][19][20][21][22][23] The metal ion in these complexes interacts with peptide ligands at the partially negatively charged carbonyl oxygen atoms on the peptide backbone, adopting multi-dentate structures where the ion is encapsulated by the ligands.…”