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

Abstract

The proteolytic processing of human amyloid precursor protein (APP) into shorter aggregating amyloid β (Aβ)-peptides, e.g., Aβ1-42, is considered a critical step in the pathogenesis of Alzheimer's disease (AD). Although APP is a well-known membrane glycoprotein carrying both N- and O-glycans, nothing is known about the occurrence of released APP/Aβ glycopeptides in cerebrospinal fluid (CSF). We used the 6E10 antibody and immunopurified Aβ peptides and glycopeptides from CSF samples and then liquid chromatography-tandem mass spectrometry for structural analysis using collision-induced dissociation and electron capture dissociation. In addition to 33 unglycosylated APP/Aβ peptides, we identified 37 APP/Aβ glycopeptides with sialylated core 1 like O-glycans attached to Thr(-39, -21, -20, and -13), in a series of APP/AβX-15 glycopeptides, where X was -63, -57, -52, and -45, in relation to Asp1 of the Aβ sequence. Unexpectedly, we also identified a series of 27 glycopeptides, the Aβ1-X series, where X was 20 (DAEFRHDSGYEVHHQKLVFF), 19, 18, 17, 16, and 15, which were all uniquely glycosylated on Tyr10. The Tyr10 linked O-glycans were (Neu5Ac)(1-2)Hex(Neu5Ac)HexNAc-O- structures with the disialylated terminals occasionally O-acetylated or lactonized, indicating a terminal Neu5Acα2,8Neu5Ac linkage. We could not detect any glycosylation of the Aβ1-38/40/42 isoforms. We observed an increase of up to 2.5 times of Tyr10 glycosylated Aβ peptides in CSF in six AD patients compared to seven non-AD patients. APP/Aβ sialylated O-glycans, including that of a Tyr residue, the first in a mammalian protein, may modulate APP processing, inhibiting the amyloidogenic pathway associated with AD.

• Authors: Adnan Halim, Gunnar Brinkmalm, Ulla Rüetschi, Ann Westman-Brinkmalm, Erik Portelius, Henrik Zetterberg, Kaj Blennow, Göran Larson, Jonas Nilsson
• Journal: Proceedings of the National Academy of Sciences of the United States of America (Proc Natl Acad Sci U S A) Vol. 108 Issue 29 Pg. 11848-53 (Jul 19 2011) ISSN: 1091-6490 [Electronic] United States
• PMID: 21712440 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Amyloid beta-Peptides
• Amyloid beta-Protein Precursor
• Threonine
• Tyrosine
• Serine

Topics

• Alzheimer Disease (metabolism, physiopathology)
• Amino Acid Sequence
• Amyloid beta-Peptides (genetics, metabolism)
• Amyloid beta-Protein Precursor (metabolism)
• Chromatography, Liquid
• Glycosylation
• Humans
• Molecular Sequence Data
• Proteomics
• Serine (metabolism)
• Tandem Mass Spectrometry
• Threonine (metabolism)
• Tyrosine (metabolism)