TANGO-Inspired Design of Anti-Amyloid Cyclic Peptides

Abstract

β-Amyloid peptide (Aβ) self-associates into oligomers and fibrils, in a process that is believed to directly lead to neuronal death in Alzheimer’s disease. Compounds that bind to Aβ, and inhibit fibrillogenesis and neurotoxicity, are of interest as an anti-Alzheimer therapeutic strategy. Peptides are particularly attractive for this purpose, because they have advantages over small molecules in their ability to disrupt protein–protein interactions, yet they are amenable to tuning of their properties through chemical means, unlike antibodies. Self-complementation and peptide library screening are two strategies that have been employed in the search for peptides that bind to Aβ. We have taken a different approach, by designing Aβ-binding peptides using transthyretin (TTR) as a template. Previously, we demonstrated that a cyclic peptide, with sequence derived from the known Aβ-binding site on TTR, suppressed Aβ aggregation into fibrils and protected neurons against Aβ toxicity. Here, we searched for cyclic peptides with improved efficacy, by employing the algorithm TANGO, designed originally to identify amyloidogenic sequences in proteins. By using TANGO as a guide to predict the effect of sequence modifications on conformation and aggregation, we synthesized a significantly improved cyclic peptide. We demonstrate that the peptide, in binding to Aβ, redirects Aβ toward protease-sensitive, nonfibrillar aggregates. Cyclic peptides designed using this strategy have attractive solubility, specificity, and stability characteristics.

Transthyretin Mimetics as Anti‐β‐Amyloid Agents: A Comparison of Peptide and Protein Approaches

“…cG8b was purified by RP-HPLC on a Vydac C18 column as previously described. [15] ThT analysis confirmed that cG8b retained the ability to inhibit Aβ aggregation (data not shown).…”

“…[13, 15] In this study, we evaluated mTTR and cG8 for their efficacy, stability, selectivity and mode of action. Our aim was to compare critical parameters that influence the choice of protein versus peptide-based compounds for anti-amyloid therapeutic strategies.…”

“…As shown in prior work, mTTR arrests Aβ aggregate growth entirely whereas cG8 redirects aggregation down a non-amyloid pathway. [13, 15] We speculate that mTTR, by retaining Aβ in a smaller and less aggregated state, decreases the quantity of Aβ deposited on cell membranes and inhibits internalization, thereby reducing Aβ-induced cellular toxicity. The striking effect of mTTR on Aβ-cell interactions was observed only when co-incubation occurred under oligomer-forming conditions.…”

“…[15, 18] Biotinylated cG8 (cG8b) was synthesized by New England Peptide (Gardner, MA) by replacing Val19 with Fmoc-Glu(biotinyl-PEG)-OH. cG8b was received as a linear peptide still on the resin.…”

“…[14] Further evolution produced cG8, which increased efficacy by increasing the adoption of an antiparallel β-strand structure and decreasing the tendency to self-associate. [15] …”