The effect of turn residues on the folding and cell-penetrating activity of β-hairpin peptides and applications toward protein delivery.
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ABSTRACT:
SUBMITTER: Miller SE
PROVIDER: S-EPMC8425381 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Although β-hairpins are widespread in proteins, there is no tool to coax any small peptide to adopt a β-hairpin conformation, regardless of sequence. Here, we report that δ-linked γ(R)-methyl-ornithine (δ MeOrn) provides an improved β-turn template for inducing a β-hairpin conformation in peptides. We developed a synthesis of protected δ MeOrn as a building block suitable for use in Fmoc-based solid-phase peptide synthesis. The synthesis begins with l-leucine and affords gram quantities of the Nα -Boc-Nδ -Fmoc-γ(R)-methyl-ornithine building block. X-ray crystallography confirms that the δ MeOrn turn unit adopts a folded structure in a macrocyclic β-hairpin peptide. CD and NMR spectroscopy allow comparison of the δ MeOrn turn template to the δ-linked ornithine (δ Orn) turn template that we previously introduced and to the popular d-Pro-Gly turn template. These studies show that the folding of the δ MeOrn turn template is substantially better than that of δ Orn and is comparable to d-Pro-Gly.
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Project description:The folding of WW domains is rate limited by formation of a beta-hairpin comprising residues from strands 1 and 2. Residues in the turn of this hairpin have reported Phi-values for folding close to 1 and have been proposed to nucleate folding. High Phi-values do not necessarily imply that the energetics of formation are a driving force for initiating folding. We demonstrate by NMR studies and molecular dynamics simulations that the first turn of the hYAP, FBP28, and PIN1 WW domains is structurally dynamic and solvent exposed in the native and folding transition states. It is, therefore, unlikely that the formation of the beta-turn per se provides the energetic driving force for hairpin folding. It is more likely that the turn acts as an easily formed hinge that facilitates the formation of the hairpin; it is a nucleus as defined by the nucleation-condensation mechanism whereby a diffuse nucleus is stabilized by associated interactions.
| S-EPMC2204123 | biostudies-literature
Project description:The turn-forming ability of a series of three-residue sequences was investigated by substituting them into a well-characterized beta-hairpin peptide. The starting scaffold, bhpW, is a disulfide-cyclized 10-residue peptide that folds into a stable beta-hairpin with two antiparallel strands connected by a two-residue reverse turn. Substitution of the central two residues with the three-residue test sequences leads to less stable hairpins, as judged by thiol-disulfide equilibrium measurements. However, analysis of NMR parameters indicated that each molecule retains a significant folded population, and that the type of turn adopted by the three-residue sequence is the same in all cases. The solution structure of a selected peptide with a PDG turn contained an antiparallel beta-hairpin with a 3:5 type I + G1 bulge turn. Analysis of the energetic contributions of individual turn residues in the series of peptides indicates that substitution effects have significant context dependence, limiting the predictive power of individual amino acid propensities for turn formation. The most stable and least stable sequences were also substituted into a more stable disulfide-cyclized scaffold and a linear beta-hairpin scaffold. The relative stabilities remained the same, suggesting that experimental measurements in the bhpW context are a useful way to evaluate turn stability for use in protein design projects. Moreover, these scaffolds are capable of displaying a diverse set of turns, which can be exploited for the mimicry of protein loops or for generating libraries of reverse turns.
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Project description:Combining natural α-amino acid residues and unnatural β-amino acid residues in a single chain leads to heterogeneous-backbone oligomers called α/β-peptides. Despite their unnatural backbones, α/β-peptides can manifest a variety of folding patterns and biological functions reminiscent of natural peptides and proteins. Moreover, incorporation of β-residues can impart useful properties to the oligomer such as improved stability to degradation by protease enzymes. α/β-Peptides have been developed that engage diverse biological targets, including proteins involved in apoptotic signalling, HIV-cell fusion, hormone signalling, and angiogenesis. For some systems, promising results obtained in vitro have paved the way for demonstrated activity in vivo, where α/β-peptides show equal potency and improved duration of effect compared to α-peptide counterparts.
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Project description:Several cationic antimicrobial peptides (AMPs) have recently been shown to display anticancer activity via a mechanism that usually entails the disruption of cancer cell membranes. In this work, we designed an 18-residue anticancer peptide, SVS-1, whose mechanism of action is designed to take advantage of the aberrant lipid composition presented on the outer leaflet of cancer cell membranes, which makes the surface of these cells electronegative relative to the surface of noncancerous cells. SVS-1 is designed to remain unfolded and inactive in aqueous solution but to preferentially fold at the surface of cancer cells, adopting an amphiphilic ?-hairpin structure capable of membrane disruption. Membrane-induced folding is driven by electrostatic interaction between the peptide and the negatively charged membrane surface of cancer cells. SVS-1 is active against a variety of cancer cell lines such as A549 (lung carcinoma), KB (epidermal carcinoma), MCF-7 (breast carcinoma), and MDA-MB-436 (breast carcinoma). However, the cytotoxicity toward noncancerous cells having typical membrane compositions, such as HUVEC and erythrocytes, is low. CD spectroscopy, appropriately designed peptide controls, cell-based studies, liposome leakage assays, and electron microscopy support the intended mechanism of action, which leads to preferential killing of cancerous cells.
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Project description:Hairpins play a central role in numerous protein folding and misfolding scenarios. Prior studies of hairpin folding, many conducted with analogs of a sequence from the B1 domain of protein G, suggest that faster folding can be achieved only by optimizing the turn propensity of the reversing loop. Based on studies using dynamic NMR, the native GB1 sequence is a slow folding hairpin (k(F)(278)=1.5 x 10(4)/s). GB1 hairpin analogs spanning a wide range of thermodynamic stabilities (DeltaG(U)(298)=-3.09 to+3.25 kJ/mol) were examined. Fold-stabilizing changes in the reversing loop can act either by accelerating folding or retarding unfolding; we present examples of both types. The introduction of an attractive side-chain/side-chain Coulombic interaction at the chain termini further stabilizes this hairpin. The 1.9-fold increase in folding rate constant observed for this change at the chain termini implies that this Coulombic interaction contributes before or at the transition state. This observation is difficult to rationalize by "zipper" folding pathways that require native turn formation as the sole nucleating event; it also suggests that Coulombic interactions should be considered in the design of systems intended to probe the protein folding speed limit.
| S-EPMC1266093 | biostudies-literature
Project description:Beta-turns are common conformations that enable proteins to adopt globular structures, and their formation is often rate limiting for folding. Beta-turn mimics, molecules that replace the i + 1 and i + 2 amino acid residues of a beta-turn, are envisioned to act as folding nucleators by preorganizing the pendant polypeptide chains, thereby lowering the activation barrier for beta-sheet formation. However, the crucial kinetic experiments to demonstrate that beta-turn mimics can act as strong nucleators in the context of a cooperatively folding protein have not been reported. We have incorporated 6 beta-turn mimics simulating varied beta-turn types in place of 2 residues in an engineered beta-turn 1 or beta-bulge turn 1 of the Pin 1 WW domain, a three-stranded beta-sheet protein. We present 2 lines of kinetic evidence that the inclusion of beta-turn mimics alters beta-sheet folding rates, enabling us to classify beta-turn mimics into 3 categories: those that are weak nucleators but permit Pin WW folding, native-like nucleators, and strong nucleators. Strong nucleators accelerate folding relative to WW domains incorporating all alpha-amino acid sequences. A solution NMR structure reveals that the native Pin WW beta-sheet structure is retained upon incorporating a strong E-olefin nucleator. These beta-turn mimics can now be used to interrogate protein folding transition state structures and the 2 kinetic analyses presented can be used to assess the nucleation capacity of other beta-turn mimics.
| S-EPMC2708776 | biostudies-literature
Project description:A light-switchable peptide is transformed with ultrashort pulses from a beta-hairpin to an unfolded hydrophobic cluster and vice versa. The structural changes are monitored by mid-IR probing. Instantaneous normal mode analysis with a Hamiltonian combining density functional theory with molecular mechanics is used to interpret the absorption transients. Illumination of the beta-hairpin state triggers an unfolding reaction that visits several intermediates and reaches the unfolded state within a few nanoseconds. In this unfolding reaction to the equilibrium hydrophobic cluster conformation, the system does not meet significant barriers on the free-energy surface. The reverse folding process takes much longer because it occurs on the time scale of 30 micros. The folded state has a defined structure, and its formation requires an extended search for the correct hydrogen-bond pattern of the beta-strand.
| S-EPMC1993841 | biostudies-literature
Project description:We examine the dynamical folding pathways of the C-terminal beta-hairpin of protein G-B1 in explicit solvent at room temperature by means of a transition-path sampling algorithm. In agreement with previous free-energy calculations, the resulting path ensembles reveal a folding mechanism in which the hydrophobic residues collapse first followed by backbone hydrogen-bond formation, starting with the hydrogen bonds inside the hydrophobic core. In addition, the path ensembles contain information on the folding kinetics, including solvent motion. Using the recently developed transition interface sampling technique, we calculate the rate constant for unfolding of the protein fragment and find it to be in reasonable agreement with experiments. The results support the validation of using all-atom force fields to study protein folding.
| S-EPMC218724 | biostudies-literature
Project description:Molecular dynamics (MD) simulations have been used to characterize the effects of backbone N-amination of residues in a model β-hairpin peptide. This modification is of considerable interest as N-aminated peptides have been shown to inhibit amyloid-type aggregation. Six derivatives of the β-hairpin peptide, which contain one, two, or four N-aminated residues, have been studied. For each peptide 100 ns MD simulations starting from the folded β-hairpin structure were performed. The effects of the N-amination prove to be very sequence dependent. N-Amination of a residue involved in interstrand hydrogen bonding (Val3) leads to unfolding of the β-hairpin, whereas N-amination of a residue toward the C-terminus (Leu11) gives fraying at the termini of the peptide. In the other derivatives the peptide remains folded, with increasing levels of N-amination reducing the right-handed twist of the β-hairpin and favoring population of a type II' rather than a type I' β-turn. MD simulations (100 ns) have also been run for each peptide starting from an unfolded extended chain. Here, the peptide with four N-aminated residues shows the most folding into the β-hairpin (34%). Analysis of the simulations shows that N-amination favors the population of β (φ, ψ) conformations by the preceding residue due to, at least in part, a network of weak NH2(i)-CO(i) and NH2(i)-CO(i-2) hydrogen bonds. It also leads to a reduction of misfolding because of changes in the hydrogen-bonding potential. Both of these features help funnel the peptide to the folded β-hairpin structure. The conformational insights provided through this work give a firm foundation for the design of N-aminated peptide inhibitors for modulating protein-protein interactions and aggregation.
| S-EPMC9795546 | biostudies-literature