Multimerization of a rationally designed nanobody for enhanced avidity toward Aβ42 oligomers.

Alzheimer's disease affects tens of millions of people worldwide and is associated with the self-assembly of the Aβ42 peptide into amyloid aggregates. Among the species formed during this process, soluble oligomeric intermediates are the most closely linked to neurotoxicity and are therefore an attractive target for both therapeutic and diagnostic strategies. Their conformational heterogeneity and transient nature, however, have so far hindered the development of reagents that recognize them selectively, and no fully quantitative biomarker of Aβ42 oligomers is widely available. To address this problem, we use a rationally designed conformation-specific single-domain antibody, DesAbO, which binds selectively to Aβ42 oligomers. By using enzyme-linked immunosorbent assay, we show that encoding self-assembling multimerization domains in the DesAbO plasmid yields multimeric variants with increased avidity toward Aβ42 oligomers. In aggregation assays, the multimeric variants inhibited Aβ42 aggregation at concentrations at which the monomeric form was no longer effective, with the SB175 trimer performing best. These results show how multimerization can be used to enhance the recognition of Aβ42 oligomers and offer a route toward diagnostic and therapeutic agents for Alzheimer's disease and other protein misfolding disorders.