Structural analysis and aggregation propensity of pyroglutamate Av(3-40) in aqueous trifluoroethanol

A hallmark of Alzheimer's disease (AD) is the accumulation of extracellular amyloid-v (Av) plaques in the brains of patients. N-terminally truncated pyroglutamate-modified Av (pEAv) has been described as a major compound of Av species in senile plaques. pEAv is more resistant to degradation, shows higher toxicity and has increased aggregation propensity and v-sheet stabilization compared to non-modified Av. Here we characterized recombinant pEAv(3-40) in aqueous trifluoroethanol (TFE) solution regarding its aggregation propensity and structural changes in comparison to its non-pyroglutamate-modified variant Av(1-40). Secondary structure analysis by circular dichroism spectroscopy suggests that pEAv(3-40) shows an increased tendency to form v-sheet-rich structures in 20% TFE containing solutions where Av(1-40) forms a-helices. Aggregation kinetics of pEAv(3-40) in the presence of 20% TFE monitored by thioflavin-T (ThT) assay showed a typical sigmoidal aggregation in contrast to Av(1-40), which lacks ThT positive structures under the same conditions. Transmission electron microscopy confirms that pEAv(3-40) aggregated to large fibrils and high molecular weight aggregates in spite of the presence of the helix stabilizing co-solvent TFE. High resolution NMR spectroscopy of recombinantly produced and uniformly isotope labeled [U-15N]-pEAv(3-40) in TFE containing solutions indicates that the pyroglutamate formation affects significantly the N-terminal region, which in turn leads to decreased monomer stability and increased aggregation propensity