Protein-bound glycogen is linked to tyrosine residues

Abstract

Tyrosine-glycogen obtained from retina proteoglycogen by exhaustive proteolytic digestion was radiolabelled with 125I. The 125I-labelled tyrosine-glycogen was degraded by amylolytic digestion to a very small radioactive product, which was identified as iodotyrosine by h.p.l.c. The amylolytic mixture used released glucose and maltose that were alpha-linked to the phenolic hydroxy group of p-nitrophenol. No free iodotyrosine was found before or after the intact [125I]iodotyrosine-glycogen was subjected to two cycles of the Edman degradation procedure. The linkage between protein and glycogen was alkali-stable. Therefore it is concluded that the protein-bound glycogen was O-glycosidically linked to the phenolic hydroxy group of tyrosine. The amino acid has not been heretofore found to be involved in the linkage of carbohydrates to proteins.

Site-specific characterization of threonine, serine, and tyrosine glycosylations of amyloid precursor protein/amyloid β-peptides in human cerebrospinal fluid

“…The analysis also revealed a hitherto unknown complex glycosylation of a tyrosine residue (Tyr10). Tyrosine residues are well-known to become phosphorylated or sulfated, but glycosylation of the Tyr hydroxyl group has only been described for glucosylation of glycogenin (28,29), and in some prokaryotic glycoproteins (30). The unique Tyr10 glycosylation thus adds another amino acid to the well-known Ser and Thr residues as possible O-glycan attachment sites for sialylated glycans on mammalian proteins.…”

Analysis of a novel linkage unit of O-linked carbohydrates from the crystalline surface layer glycoprotein of Clostridium thermohydrosulfuricum S102-70

“…3) was determined by one-and two-dimensional proton and carbon NMR spectroscopy techniques and will be published elsewhere (8). No (2,29). The involvement of tyrosine was concluded from iodination experiments (2).…”

“…No (2,29). The involvement of tyrosine was concluded from iodination experiments (2). The anomeric configuration of glucose was deduced from the specificity of the enzyme mixture used for the degradation reaction (29).…”

Structural Aspects of the O‐glycosylation Linkage in Glycopeptides via MD Simulations and Comparison with NMR Experiments

“…N‐ and O‐glycosylation are the two most common types of glycosylation where glycans are attached to proteins via either the nitrogen of Asn (N‐linked) or the oxygen of Ser/Thr (O‐linked). In some limited cases O‐glycans can be attached to modified hydroxyproline and hydroxylysine and in a very rare event, O‐glycosidic linkage of α ‐glucose to tyrosine is observed in glycogen containing eukaryotic cells . The consensus sequence for N‐glycosylation is Asn‐X‐Thr/Ser where X is any amino acid different than Proline.…”