Inhibitors of amyloid toxicity based on β-sheet packing of Aβ40 and Aβ42

Amyloid fibrils associated with Alzheimer's disease and a wide range of other neurodegenerative diseases have a cross beta-sheet structure, where main chain hydrogen bonding occurs between beta-strands in the direction of the fibril axis. The surface of the beta-sheet has pronounced ridges and grooves when the individual P-strands have a parallel orientation and the amino acids are in-register with one another. Here we show that in A amyloid fibrils, Met35 packs against Gly33 in the C-terminus of A beta 40 and against Gly37 in the C-terminus of A beta 42. These packing interactions suggest that the protofilament subunits are displaced relative to one another in the A beta 40 and A beta 42 fibril structures. We take advantage of this corrugated structure to design a new class of inhibitors that prevent fibril formation by placing alternating glycine and aromatic residues on one face of a beta-strand. We show that peptide inhibitors based on a GxFxGxF framework disrupt sheet-to-sheet packing and inhibit the formation of mature A beta fibrils as assayed by thioflavin T fluorescence, electron microscopy, and solid-state NMR spectroscopy. The alternating large and small amino acids in the GxFxGxF sequence are complementary to the corresponding amino acids in the IxGxMxG motif found in the C-terminal sequence of A beta 40 and A beta 42. Importantly, the designed peptide inhibitors significantly reduce the toxicity induced by A beta 42 on cultured rat cortical neurons.