Sulfonyl-γ-AAs act as β-turn templates, robustly inducing β-sheet conformation in macrocyclic peptides

Designing synthetic β-sheet mimics remains a significant challenge despite their critical role in protein secondary structures and diverse biological functions. These structures are essential for protein-protein interactions and are implicated in various diseases, including Alzheimer's disease where amyloid-beta (Aβ) aggregation involves the formation of toxic β-sheet fibrils. Current approaches struggle with sequence-dependent folding, limiting the development of stable, functional mimetics. A robust method for inducing predictable β-turn structures could unlock new avenues for therapeutic development and advanced biomaterials by enabling the creation of stable, antiparallel β-sheet architectures.

Researchers synthesized novel sulfonyl-γ-AAs (γ-substituted-N-sulfonyl-N-aminoethyl amino acids) and incorporated them into macrocyclic peptides. They performed single-crystal X-ray diffraction on sulfonyl-γ-AAs B1 and a macrocyclic peptide BS-1 containing these residues to elucidate their precise structural conformation. To further characterize the induced secondary structures, circular dichroism (CD) spectroscopy was applied to peptides BS-6 through BS-9. Additionally, 2D-NMR studies were conducted to confirm the folded solution structures and their consistency with the crystal structures, providing comprehensive insights into the β-sheet induction mechanism.

Sulfonyl-γ-AAs were confirmed as effective artificial β-turn inducers, driving stable β-sheet conformations in macrocyclic peptides. Single-crystal X-ray diffraction of sulfonyl-γ-AAs B1 and macrocyclic peptide BS-1 revealed that the sulfonyl-γ-AAs adopt a β-turn-like conformation. This conformation is stabilized by both intramolecular hydrogen bonding and the intrinsic curvature of the sulfonamido moiety, which collectively facilitate the formation of a folded β-sheet structure with defined amino acid residues. This work represents the first crystallographic validation of a polyalanine β-sheet structure enforced by a β-turn mimic. Moreover, circular dichroism (CD) spectroscopy of BS-6 to BS-9 displayed characteristic minima between 208-214 nm, consistent with robust β-sheet signatures. 2D-NMR studies further corroborated these findings, revealing well-folded solution structures that were consistent with the X-ray crystal structures.

These results establish sulfonyl-γ-AAs as a versatile class of β-turn templates that effectively drive β-sheet formation, enabling the creation of novel macrocyclic antiparallel β-sheet mimics.