Protonated α- N -Acetyl Galactose Glycopeptide Dissociation Chemistry
Résumé
We recently provided mass spectrometric, H/D labeling, and computational evidence of pyranose to furanose N-Acetylated ion isomerization reactions occurring prior to glycosidic bond cleavage in both O-and N-linked glycosylated amino acid model systems (Phys. Chem. Chem. Phys., 2021, 23, 23256-23266). These reactions occurred irrespective of glycosidic linkage stereochemistry (α/β) and N-Acetylated hexose structure (GlcNAc/GalNAc). In the present article we test the generality of the preceding findings by examining Threonyl α-GalNAc glycosylated peptides. We utilize computational chemistry to compare the various dissociation and isomerization pathways accessible with collisional activation. We then interrogate the structure(s) of the resulting charged glycan and peptide fragments with infrared "action" spectroscopy. Isomerization of the original pyranose, protonated glycopeptide, [AT(GalNAc)A+H] + , is predicted to be facile compared to direct dissociation, as is glycosidic bond cleavage of the newly formed furanose form. i.e., furanose oxazolinium ion structures are predicted to predominate. IR action spectra for the m/z 204, C8H14N1O5 + , glycan fragment population support this prediction. The IR action spectra of the complementary m/z 262, peptide fragment are assigned as a mixture of the lowest energy structures of [ATA+H] + consistent with the literature. If general, the change to a furanose m/z 204 product ion structure fundamentally alters the ion population available for MS 3 dissociation and glycopeptide sequence identification.
Domaines
Chimie
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