Development of Alkaline Phosphatase-Fused Mouse Prion Protein and Its Application in Toxic Aß Oligomer Detection.

Amyloid ß (Aß) oligomers play a key role in the progression of Alzheimer's disease (AD). Multiple forms of Aß assemblies have been identified by in vitro and in vivo analyses; however, it is uncertain which oligomer is highly neurotoxic. Thus, understanding the pathogenesis of AD by detecting toxic Aß oligomers is crucial. In this study, we report a fusion protein of cellular prion protein (PrPc) and alkaline phosphatase (ALP) from Escherichia coli as a sensing element for toxic Aß oligomers. Since the N-terminus domain of PrPc (residue 23-111) derived from mice is known to bind to toxic Aß oligomers in vitro, we genetically fused PrPc23-111 to ALP. The developed fusion protein, PrP-ALP, retained both the binding ability of PrPc and enzymatic activity of ALP. We showed that PrP-ALP strongly bound to high molecular weight (HMW) oligomers but showed little or no affinity toward monomers. The observation that PrP-ALP neutralized the toxic effect of Aß oligomers indicated an interaction between PrP-ALP and toxic HMW oligomers. Based on ALP activity, we succeeded in detecting Aß oligomers. PrP-ALP may serve as a powerful tool for detecting toxic Aß oligomers that may be related to AD progression.