Beyond Natural Limitations: Long‐Range Influence of Non‐Natural Flexible and Rigid β‐Turn Mimetics in a Native β‐Hairpin Motif

Abstract

β‐Turns mediate diverse protein recognition processes, although dihedral angle preferences of canonical amino acids limit accessible β‐turn geometries. Organic synthesis can go beyond these limitations and either increase the mobility of a β‐turn or constrain it inside a bicyclic ring. Nine β‐turn dipeptides are studied here in the isolated β‐hairpin of the miniprotein Foldon, which is only moderately structured in the absence of the native protein environment. The dipeptide mimetics, which vary the backbone flexibility from linear alkyl chains to bicyclic dipeptides (Hot=Tap), are ranked against each other with regard to their hairpin‐stabilizing capacities. NMR‐derived parameters and melting temperatures correlate the backbone rigidity of the β‐turns with the hairpin population. In contrast to the general expectation, highly populated hairpins are not only observed for rigid dipeptides, but also for selected flexible amino acids in the i + 1 and i + 2 positions of the β‐turn.

Tunable CH/π Interactions within a Tryptophan Zipper Motif to Stabilize the Fold of Long β-Hairpin Peptides

“…As the energy of hydrogen bonds in XH/π interactions is strongly distance dependent (1/r 3 ), the CSDs are expected to deviate from linearity upon heating. 32,73,74 Indeed, this is exactly what we found with the large resonance shifts of H ε3 and H β2 at both edge W4/W17 and the H N of G14 (see Table S9) characterized by a markedly nonlinear behavior at temperatures comparable to the global hairpin denaturation T m ∼ 50 °C obtained in the CD study. H N and H ar chemical shifts typically display a linear and negative temperature dependence (Δδ/ΔT ≤ 0, within experimental uncertainty), although it is striking that protons involved in XH/π interactions deviate strongly from linearity into melting curves resembling a local unfolding (Δδ/ΔT ≥ 0, up to 25 ppb/K at T m ).…”

High five! Methyl probes at five ring positions of phenylalanine explore the hydrophobic core dynamics of zinc finger miniproteins

“…31 The hydroxy groups are liberated from the acetonide during acidic cleavage from the resin. 34 After successful synthesis we observed higher purity, both crude and purified, (Supporting Information), higher yield and better solubility. NMR analysis of the apo peptide reveals, that the Hot=Tap derivative exhibits a pre-folded species with β-turn indications.…”

“…Here, we introduce strongly β-turn stabilizing Hot Tap 31 which has been incorporated into several β-turn motifs 32,33 and displays superior conformational restriction of hairpin turns, in comparison to BTD. 34 After the substitution of the natural β-turn, we observed an increased yield, crude purity, and solubility for the zinc finger derivative, while retaining the fold of the natural zinc finer peptide and the BTD derivative. As expected for a well-folded structure, the influence of the stronger restriction by Hot Tap is nearly indistinguishable from BTD which lacks preferred lactam puckering and β-branching.…”

Assembly of synthetic Aβ miniamyloids on polyol templates

“…Compound 5 combines side-chain cis -diol functionality for boronic ester formation and the potential of controlled oligomerization by peptide chemistry. Azido ester 5 is a precursor of the dipeptide Hot=Tap, which serves as a β-turn mimic in peptides and proteins [ 24 – 26 ]. Alternatively, Fmoc-Hot=Tap-OH ( 8 , Fig.…”