Heterotypic Interactions between the 40- and 42-Residue Isoforms of β-Amyloid Peptides on Lipid Bilayer Surfaces

Co-aggregation involving different amyloidogenic sequences has been emphasized recently in the modified amyloid cascade hypothesis. Yet, molecular-level interactions between two predominant β-amyloid peptide sequences, Aβ₄₀ and Aβ₄₂, in the fibrillation process in membrane-mimicked environments remain unclear. Here, we report biophysical evidence that demonstrates the molecular-level interactions between Aβ₄₀ and Aβ₄₂ at the membrane-associated conucleation stage using dynamic nuclear polarization-enhanced solid-state NMR spectroscopy. These residue-specific contacts are distinguished from those reported in mature fibrils formed by either Aβ₄₀ or Aβ₄₂. Meanwhile, site-specific interactions between Aβ and lipid molecules and modulation of microsecond-time-scale lipid dynamics are observed, which may be responsible for the more rapid and significant membrane content leakage compared to that with Aβ₄₀ alone.