Switch-peptides: design and characterization of controllable super-amyloid-forming host-guest peptides as tools for identifying anti-amyloid agents

Several amyloid-forming proteins are characterized by the presence of hydrophobic and highly amyloidogenic core sequences that play critical roles in the initiation and progression of amyloid fibril formation. Therefore targeting these sequences represents a viable strategy for identifying candidate molecules that could interfere with amyloid formation and toxicity of the parent proteins. However, the highly amyloidogenic and insoluble nature of these sequences has hampered efforts to develop high-throughput fibrillization assays. Here we describe the design and characterization of host-guest switch peptides that can be used for in vitro mechanistic and screening studies that are aimed at discovering aggregation inhibitors that target highly amyloidogenic sequences. These model systems are based on a host-guest system where the amyloidogenic sequence (guest peptide) is flanked by two beta-sheet-promoting (Leu-Ser)(n) oligomers as host sequences. Two host-guest peptides were prepared by using the hydrophobic core of Abeta comprising residues 14-24 (HQKLVFFAEDV) as the guest peptide with switch elements inserted within (peptide 1) or at the N and C termini of the guest peptide (peptide 2). Both model peptides can be triggered to undergo rapid self-assembly and amyloid formation in a highly controllable manner and their fibrillization kinetics is tuneable by manipulating solution conditions (for example, peptide concentration and pH). The fibrillization of both peptides reproduces many features of the full-length Abeta peptides and can be inhibited by known inhibitors of Abeta fibril formation. Our results suggest that this approach can be extended to other amyloid proteins and should facilitate the discovery of small-molecule aggregation inhibitors and the development of more efficacious anti-amyloid agents to treat and/or reverse the pathogenesis of neurodegenerative and systemic amyloid diseases

Switch-peptides as folding precursors in self-assembling peptides and amyloid fibrillogenesis

The study of conformational transitions of peptides has obtained considerable attention recently because of their importance as a mol. key event in a variety of degenerative diseases. However, the study of peptide self-assembly into beta-sheets and amyloid beta (Abeta) fibrils is strongly hampered by their difficult synthetic access and low soly. We have recently developed a new concept termed "switch-peptides" that allows the controlled onset of polypeptide folding and misfolding at physiol. conditions. As a major feature, the folding process is initiated by chem. or enzyme triggered O,N-acyl migration in flexible and sol. folding precursors contg. Ser- or Thr-derived switch (S)-elements. The elaborated methodologies are exemplified for the in situ conversion of NPY- and Cyclosporine A-derived prodrugs, as well as for the onset and reversal of alpha and beta conformational transitions in Abeta peptides. In combining orthogonally addressable switch-elements, the consecutive switching on of S-elements gives new insights into the role of individual peptide segments ("hot spots") in early processes of polypeptide self-assembly and fibrillogenesis. Finally, the well-known secondary structure disrupting effect of pseudoprolines (Psi Pro) is explored for its use as a building block (S-element) in switch-peptides. To this end, synthetic strategies are described, allowing for the prepn. of Psi Pro-contg. folding precursors, exhibiting flexible random-coil conformations devoid of fibril forming propensity. The onset of beta-sheet and fibril formation by restoring the native peptide chain in a single step classify Psi Pro-units as the most powerful tool for inhibiting peptide self-assembly, and complement the present methodologies of the switch-concept for the study of fibrillogenesis

Switch peptides in statu nascendi: Induction of conformational transitions relevant to degenerative diseases

A novel concept for triggering conformational transitions, and thus changes in structure and function, in peptides with a switching element S provides intriguing perspectives for studying mol. processes that play a key role, for example, in early events of Alzheimer's disease. [on SciFinder (R)

Switch-peptides as folding precursors in amyloid fibrillogenesis

Intramol. O,N-acyl migration reactions were used as structural switch (S-elements) from a depsipeptide bond contg., unfolded state (Soff) to an all-amide, native states (Son). Chem. or enzymically triggered acyl migrations allowed for the controlled induction of folding events in the process of primary structure evolution, i.e., in statu nascendi (ISN) of the native mol. In the (Soff)-state, the switch-peptide contg. two enzyme (dipeptidyl peptidase IV and pyroglutamate aminopeptidase) cleavable S-elements proved to be highly sol. at physiol. conditions, thus facilitating HPLC purifn. and structural characterization. The conformational decoupling of the individual peptide blocks resulted in a flexible random coil conformation, showing no tendency for self-assocn. or fibril formation after 24 h. In contrast, after selective triggering of the acyl migrations, significant changes in the physicochem. and conformational properties paralleled by the onset of Abeta-like fibrils were obsd