Thermodynamic Analysis of β-Hairpin-Forming Peptides from the Thermal Dependence of¹H NMR Chemical Shifts

Abstract

The temperature dependence of the (1)H chemical shifts of six designed peptides previously shown to adopt beta-hairpin structures in aqueous solution has been analyzed in terms of two-state (beta-hairpin left arrow over right arrow coil) equilibrium. The stability of the beta-hairpins formed by these peptides, as derived from their T(m) (midpoint transition temperature) values, parallels in general their ability to adopt those structures as deduced from independent NMR parameters: NOEs, Deltadelta(C)(alpha)(H), Deltadelta(C)(alpha), and Deltadelta(C)(beta) values. The observed T(m) values are dependent on the particular position within the beta-hairpin that is probed, indicating that their folding to a beta-hairpin conformation deviates from a "true" two-state transition. To obtain individual T(m) values for each hairpin region in each peptide, a simplified model of a successive uncoupled two-state equilibrium covering the entire process has been applied. The distribution of T(m) values obtained for the different beta-hairpin regions (turn, strands, backbone, side chains) in the six analyzed peptides reveals a similar pattern. A model for beta-hairpin folding is proposed on the basis of this pattern and the reasonable assumption that regions showing higher T(m) values are the last ones to unfold and, presumably, the first to form. With this assumption, the analysis suggests that turn formation is the first event in beta-hairpin folding. This is consistent with previous results on the essential role of the turn sequence in beta-hairpin folding.

Context‐Dependence of the Contribution of Disulfide Bonds to β‐Hairpin Stability

“…Peptide design: The model peptides were derived from peptide 1 (Figures 1 and 2), a 15-residue peptide previously shown to adopt a monomeric 3:5 b-hairpin with a type I + G1 b-bulge turn in aqueous solution, [18][19][20] by replacing different pairs of facing residues by Cys residues. These peptides were named according to the Cys positions ( Figure 2).…”

“…(ppm)) as a function of peptide sequence provide corroborating evidence that the peptides adopt the expected 3:5 b-hairpins. [18][19][20] Excluding the N-and C-terminal residues, whose chemical shifts can be affected by charge-end effects, the profiles displayed by peptides C1C15, C2C14, C3C13, and C5C11 in their oxidized and reduced forms (Figures 4 and 5 and Figures S1 and S2 in Supporting Information) consist of two stretches with positive Dd C a H , Dd NH , and Dd C b values, Figure 3. NOESY spectral region of peptides C1C15o (top) and C1C15r (bottom) in D 2 O at pH 5.5 and 5 8C.…”

Cross-Strand Coupling and Site-Specific Unfolding Thermodynamics of a Trpzip β-Hairpin Peptide Using 13C Isotopic Labeling and IR Spectroscopy

“…The resulting thermal denaturation curves are often characterized by very broad transitions. [43][44][45][46][47] Increase in the number of interstrand hydrophobic interactions has been shown to stabilize -hairpin structures and result in somewhat more sigmoidal denaturation profiles in trpzips; 1,30,48 however, there can be a tendency for such peptide sequences to aggregate. 24 Due to their small size, trpzips have also been a subject of many theoretical studies.…”

The C-terminal Domains of Vertebrate CstF-64 and Its Yeast Orthologue Rna15 Form a New Structure Critical for mRNA 3′-End Processing

“…Thus, the processing defect caused by the L214P mutation may result from a destabilization of the Rna14 interaction. Interestingly, with the program BEHAIRPRED (81), this segment is predicted to form a 2:2 ␤-hairpin with a type IЈ ␤-turn, in which Leu 214 would form part of the turn sequence that is crucial for the formation and stability of ␤-hairpin structures (82).…”