Development of ß-sheet structure in Aß aggregation intermediates diminishes exposed hydrophobic surface area and enhances proinflammatory activity.

Three decades of research, both in vitro and in vivo, have demonstrated the conformational heterogeneity that is displayed by the amyloid ß peptide (Aß) in Alzheimer's disease (AD). Understanding the distinct properties between Aß conformations and how conformation may impact cellular activity remain open questions, yet still continue to provide new insights into protein misfolding and aggregation. In particular, there is interest in the group of soluble oligomeric prefibrillar Aß species comprising lower molecular weight oligomers up to larger protofibrils. In the current study, a number of strategies were utilized to separate Aß protofibrils and oligomers and show that the smaller Aß oligomers have a much different conformation than Aß protofibrils. The differences were consistent for both Aß40 and Aß42. Protofibrils bound thioflavin T to a greater extent than oligomers, and were highly enriched in ß-sheet secondary structure. Aß oligomers possessed a more open structure with significant solvent exposure of hydrophobic domains as determined by tryptophan fluorescence and bis-ANS binding, respectively. The protofibril-selective antibody AbSL readily discerned conformational differences between protofibrils and oligomers. The more developed structure for Aß protofibrils ultimately proved critical for provoking the release of tumor necrosis factor α from microglial cells. The findings demonstrated a dependency on ß-sheet structure for soluble Aß aggregates to cause a microglial inflammatory response. The Aß aggregation process yields many conformationally-varied species with different levels of ß-structure and exposed hydrophobicity. The conformation elements likely determine biological activity and pathogenicity.

Development of a Simple and Effective Lipid-A Antagonist Based on Computational Prediction.

Sepsis is a serious medical condition characterized by bacterial infection and a subsequent massive systemic inflammatory response. In an effort to identify compounds that block lipopolysaccharide (LPS)-induced inflammation reported herein is the development of simple Lipid-A analogues that lack a disaccharide core yet still possess potent antagonistic activity against LPS. The structure of the new lead compound was developed based on predictive computational experiments. LPS antagonism by the lead compound was not straightforward, and a biphasic effect was observed suggesting a possibility of more than one binding site. An IC50 value of 13 nM for the new compound was determined for the possible high affinity site. The combination of computational, synthetic, and biological studies revealed new structural determinants of these simplified analogues. It is expected that the acquired information will aid future design of LPS targeting glycopharmaceuticals.