N-terminal engineering of amyloid-β-binding Affibody molecules yields improved chemical synthesis and higher binding affinity

The aggregation of amyloid-beta (A beta) peptides is believed to be a major factor in the onset and progression of Alzheimer's disease Molecules binding with high affinity and selectivity to A beta-peptides are important tools for investigating the aggregation process An A beta-binding Affibody molecule, Z(A beta 3), has earlier been selected by phage display and shown to bind A beta(1-40) with nanomolar affinity and to inhibit A beta-peptide aggregation In this study, we create truncated functional versions of the Z(A beta 3) Affibody molecule better suited for chemical synthesis production Engineered Affibody molecules of different length were produced by solid phase peptide synthesis and allowed to form covalently linked homodimers by S-S-bridges The N-terminally truncated Affibody molecules Z(A beta 3)(12-58), Z(A beta 3)(15-58), and Z(A beta 3)(18-58) were produced in considerably higher synthetic yield than the corresponding full-length molecule Z(A beta 3)(1-58) Circular dichroism spectroscopy and surface plasmon resonance-based biosensor analysis showed that the shortest Affibody molecule, Z(A beta 3)(18-58), exhibited complete loss of binding to the A beta(1-40)-peptide, while the Z(A beta 3)(12-58) and Z(A beta 3)(15-58) Affibody molecules both displayed approximately one order of magnitude higher binding affinity to the A beta(1-40)-peptide compared to the full-length Affibody molecule Nuclear magnetic resonance spectroscopy showed that the structure of A beta(1-40) in complex with the truncated Affibody dimers is very similar to the previously published solution structure of the A beta(1-40)-peptide in complex with the full-length Z(A beta 3) Affibody molecule This indicates that the N-terminally truncated Affibody molecules Z(A beta 3)(12-58) and Z(A beta 3)(15-58) are highly promising for further engineering and future use as binding agents to monomeric A beta(1-40)