Inhibition of toxicity and protofibril formation in the amyloid-β peptide β(25-35) using N-methylated derivatives

beta(25-35) is a fragment of beta-amylold that retains its wild-type properties. N-methylated derivatives of beta(25-35) can block hydrogen bonding on the outer edge of the assembling amylold, so preventing the aggregation and inhibiting the toxicity of the wildtype peptide. The effects are assayed by Congo Red and thioflavin T binding, electron microscopy and an MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] toxicity assay. N-methyl-Gly-25 has similar properties to the wild-type, while five other methylation sites have varying effects on prefolded fibrils and fibril assembly. In particular, N-methyl-Gly-33 is able to completely prevent fibril assembly and reduces the toxicity of prefolded amyloid. With N-methy-Leu-34 the fibril morphology is altered and toxicity reduced. A preliminary study of beta(25-35) structure in aqueous solution was made by small-angle neutron scattering (SANS). The protofibrillar aggregates are best described as a disc of radius 140 Angstrom and height 53 Angstrom (1 Angstrom = 0.1 nm), though the possibility of polydisperse aggregates cannot be ruled out. No aggregates form in the presence of N-methyl-Gly-33. We suggest that the use of N-methylated derivatives of amyloidogenic peptides and proteins could provide a general solution to the problem of amylold deposition and toxicity and that SANS is an important technique for the direct observation of protofibril formation and destruction in solution.