Title : 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 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