Aberrant proteolytic processing of amyloid precursor protein (APP) can alter amyloid-β (Aβ) peptide trafficking, with recent studies implicating MUC1-type O-glycosylation as a modulatory factor. In this study, we synthesized native and Swedish-mutated (Lys670Asn/Met671Leu) APP glycopeptides spanning the Aβ(1-23) region, including the β- and α-secretase cleavage sites, and introduced O-GalNAc moieties at Thr663, Ser667, and/or Tyr681. Circular dichroism (CD) revealed conformational changes governed by the glycosylation site and glycan density. Increased glycan valency favored the stabilization of β-turn-rich structures typically associated with oligomeric and prefibrillar intermediates. The Swedish mutation enhanced β-secretase (BACE1) cleavage, especially when Ser667 was glycosylated, while additional glycans favored α-secretase (ADAM10) processing. However, this shift was not sufficient to counterbalance the amyloidogenic pathway. Similarly, Ser667 glycosylation promoted fibril formation in coincubation assays with Aβ40, while di- and triglycosylated peptides disrupted fibril architecture and favored oligomer formation, as confirmed by ThT kinetics, AFM/TEM imaging, and dynamic light scattering. These findings highlight the critical role of mutation and site-specific glycosylation in shaping APP proteolytic processing, secondary structure, and aggregation behavior, underscoring their importance for understanding APP function in both healthy and diseased states.
Navarro et al. (Wed,) studied this question.