Solution State Characterization of Amyloid β-Derived Diffusible Ligands

Abstract

A growing body of evidence suggests that soluble oligomeric forms of the amyloid beta peptide known as amyloid-derived diffusible ligands (ADDLs) are the toxic species responsible for neurodegeneration associated with Alzheimer's disease. Accurate biophysical characterization of ADDL preparations is hampered by the peptide's strong tendency to self-associate and the effect of factors such as ionic strength, temperature, and pH on its behavior. In addition, amyloid peptides are known to interact with common laboratory excipients, specifically detergents, further complicating the results from standard analytical methods such as denaturing polyacrylamide gel electrophoresis. We have studied the solution behavior of various amyloid peptide preparations using analytical ultracentrifugation and size exclusion chromatography coupled with multiangle laser light scattering. Our results indicate that ADDL preparations exist in solution primarily as a binary mixture of a monomeric peptide and high-molecular mass oligomers. We relate our findings to previously described characterizations utilizing atomic force microscopy and electrophoretic methods and demonstrate that low-molecular mass oligomers identified by gel electrophoresis likely represent artifacts induced by the peptide's interaction with detergent, while atomic force microscopy results are likely skewed by differential binding of monomeric and oligomeric peptide species. Finally, we confirm that only the high-molecular mass oligomeric components of an ADDL preparation are capable of binding to subpopulations of primary hippocampal neurons in vitro.

Preparation and characterization of toxic Aβ aggregates for structural and functional studies in Alzheimer's disease research

“…1b), despite the fact that these species elute in the void volume of Superdex 75 ( > 70 kDa), which should only contain PFs. This anomalous migration on SDS gels by protofibrils and oligomers of sAβ has also been reported by other groups 13,83 . There are different possibilities to explain these experimental observations; (i) some of these LMW oligomers may exist in rapid equilibrium with protofibrils; (ii) these oligomers may not exist in solution but form as a result of SDS-induced disassociation of protofibrils; or (iii) formation of these species may be induced by the interaction of Aβ with SDS micelles as described above 73 .…”

Selection and structural analysis of de novo proteins from an α3β3 genetic library

“…As a result, these proteins may have interacted non-specifically with the gel matrix of the dextran-based column. 27 Thus, peaks corresponding to the molecular weight of these proteins could not be observed. In this regard, GFP selection is a preferred method to identify the folded proteins.…”

Aβ42 Neurotoxicity Is Mediated by Ongoing Nucleated Polymerization Process Rather than by Discrete Aβ42 Species

“…9,10). Although the toxic oligomer hypothesis has emerged as one of the major current working hypotheses in AD research, the development of effective diagnostic tools and therapies on the basis of this hypothesis has yet to be realized (11)(12)(13). This is partially due to the fact that identification of a single toxic A␤ species that correlates with AD progression and severity remains elusive.…”

“…Despite significant efforts by different groups to isolate specific intermediates along the amyloid formation pathway (12, 18 -22), the inherent heterogeneity of the process and metastable nature of A␤ oligomers (11)(12)(13) have precluded the isolation of a single toxic species. Unless covalently crosslinked (23), A␤ oligomers do not exist as stable entities, i.e.…”