Conformational Dynamics of Amyloid β-Protein Assembly Probed Using Intrinsic Fluorescence † (original) (raw)

Formation of toxic oligomeric and fibrillar structures by the amyloid-protein (A) is linked to Alzheimer's disease (AD). To facilitate the targeting and design of assembly inhibitors, intrinsic fluorescence was used to probe assembly-dependent changes in A conformation. To do so, Tyr was substituted in A 40 or A 42 at position 1, 10 (wild type), 20, 30, 40, or 42. Fluorescence then was monitored periodically during peptide monomer folding and assembly. Electron microscopy revealed that all peptides assembled readily into amyloid fibrils. Conformational differences between A 40 and A 42 were observed in the central hydrophobic cluster (CHC) region, Leu 17-Ala 21. Tyr 20 was partially quenched in unassembled A 40 but displayed a significant and rapid increase in intensity coincident with the maturation of an oligomeric, R-helix-containing intermediate into amyloid fibrils. This process was not observed during A 42 assembly, during which small decreases in fluorescence intensity were observed in the CHC. These data suggest that the structure of the CHC in A 42 is relatively constant within unassembled peptide and during the self-association process. Solvent accessibility of the Tyr ring was studied using a mixed solvent (dimethyl sulfoxide/water) system. [Tyr 40 ]A 40, [Tyr 30 ]A 42, and [Tyr 42 ]A 42 all were relatively shielded from solvent. Analysis of the assembly dependence of the sitespecific intrinsic fluorescence data suggests that the CHC is particularly important in controlling A 40 assembly, whereas the C-terminus plays the more significant role in A 42 assembly.

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