Exploiting a 13C-labelled heparin analogue for in situsolid-state NMR investigations of peptide-glycan interactions within amyloid fibrils

Abstract

Pathological amyloid deposits are mixtures of polypeptides and non-proteinaceous species including heparan sulfate proteoglycans and glycosaminoglycans (GAGs). We describe a procedure in which a ¹³C-labelled N-acetyl derivative of the GAG heparin ([¹³C-CH₃]NAcHep) serves as a useful probe for the analysis of GAG-protein interactions in amyloid using solid-state nuclear magnetic resonance (SSNMR) spectroscopy. NAcHep emulates heparin by enhancing aggregation and altering the fibril morphology of Aβ_1–40, one of the β-amyloid polypeptides associated with Alzheimer's disease, and α-synuclein, the major protein component of Lewy bodies associated with Parkinson's disease. ¹³C SSNMR spectra confirm the presence of [¹³C-CH₃]NAcHep in Aβ_1–40 fibril deposits and detect dipolar couplings between the glycan and arginine R₅ at the Aβ_1–40 N-terminus, suggesting that the two species are intimately mixed at the molecular level. This procedure provides a foundation for further extensive investigations of polypeptide-glycan interactions within amyloid fibrils.