Aggregation of β-amyloid (Aβ) is implicated in the pathology of Alzheimer's disease. Development of a robust strategy to detect Aβ oligomeric intermediates, which have been identified as significant toxic agents, would be highly beneficial in the screening of drug candidates as well as enhancing our understanding of Aβ oligomerization. Rapid, specific and quantitative detection, currently unavailable, would be highly preferred for accurate and reliable probing of transient Aβ oligomers. Here, we report the development of a novel peptide probe, PG46, based on the nature of Aβ self-assembly and the conformation-sensitive fluorescence of the biarsenical dye, FlAsH. PG46 was found to bind to Aβ oligomers and displayed an increase in FlAsH fluorescence upon binding. No such event was observed when PG46 was co-incubated with Aβ low-molecular-weight species or Aβ fibrils. Aβ oligomer detection was fast, and occurred within one hour without any additional sample incubation or preparation. We anticipate that the development of a strategy for detection of amyloid oligomers described in this study will be directly relevant to a host of other amyloidogenic proteins.

Aggregation of β-amyloid (Aβ) is implicated in the pathology of Alzheimer's disease (AD). A considerable amount of data has identified soluble Aβ oligomers as potentially significant toxic agents. Rapid, specific and quantitative detection is preferred for accurate profiling of structurally unstable Aβ oligomers as well as for implementation of high-throughput assays for pharmaceutical applications. PG46 is an engineered Aβ variant, constructed by integrating Aβ self-recognition sequences with the conformation-sensitive biarsenical fluorescent dye, FlAsH. PG46 was found to be an effective peptide probe, which detected Aβ oligomers specifically and quantitatively within one hour. However, PG46 was highly aggregation-prone and displayed a limited repertoire of detectable Aβ oligomers. Here, we report the creation of a novel molecular probe, PG44, by C-terminal truncation of PG46. PG44 exhibited a reduced self-aggregation propensity and a different conformation when compared to PG46, and generated specific FlAsH fluorescence signals as a result of binding to various Aβ oligomers, including those not readily detectable by PG46. We also show that sensitivity of PG44 for detection of certain Aβ oligomers may be increased by lowering PG44 concentration and thus decreasing the extent of self-aggregation of PG44. Our results suggest that PG44 can serve as an important molecular probe with a broadened repertoire of detectable Aβ oligomeric aggregates. We believe that detection of Aβ oligomers using our peptide probe would potentially contribute toward a better understanding of the molecular basis of Aβ oligomerization and the development of Aβ oligomer-based early diagnostics as well as therapeutic drugs targeting Aβ oligomers.

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