An In-tether Chiral Center Modulates the Helicity, Cell Permeability, and Target Binding Affinity of a Peptide

The facile and visualizable identification of broad-spectrum inhibitors of MDM2/p53 using co-expressed protein complexes

MDM2 is a well-known oncoprotein overexpressed in a variety of cancers, and the identification of inhibitors that disrupt the MDM2/p53 interaction is of great interest in anticancer drug development. Here we designed a platform for the facile and visualizable identification of inhibitors of MDM2 using co-expressed protein complexes of MDM2/p53. A hexahistidine-tag on MDM2 allows the binding of the protein complex to the Ni-NTA affinity resin, while the fluorescent protein fused to p53 enables the direct visualization of the interaction of p53 with MDM2. Hence, the inhibition of the MDM2/p53 interaction can be observed with the naked eye. The assay can be set up by directly loading cell lysate to the Ni-NTA affinity resin, and no chemical modification of proteins is needed. In addition to the qualitative analyses, the binding affinity of inhibitors to the MDM2 protein can be quantified by fluorescence titration. The applications of this system have been verified using small molecules and peptide inhibitors. As a proof of concept, we screened a small library using this platform. Interestingly, two types of novel inhibitors of MDM2, including cyclohexyl-triphenylamine derivatives and platinum complexes, were identified and their binding affinities were obtained. Quantitative measurements show that these new types of inhibitors demonstrate a high binding affinity (up to K_d = 51.9 nM) to MDM2.

Ordered and Isomerically Stable Bicyclic Peptide Scaffolds Constrained through Cystine Bridges and Proline Turns

Bicyclic peptides are attractive scaffolds for the design of potent protein binders and new therapeutics. However, peptide bicycles constrained through disulfide bonds are rarely stable or tolerant to sequence manipulation owing to disulfide isomerization, especially for peptides lacking a regular secondary structure. Herein, we report the discovery and identification of a class of bicyclic peptide scaffolds with ordered but irregular secondary structures. These peptides have a conserved cysteine/proline framework for directing the oxidative folding into a fused bicyclic structure that consists of four irregular turns and a 3₁₀ helix (characterized by NMR spectroscopy). This work shows that bicyclic peptides can be stabilized into ordered structures by manipulating both the disulfide bonds and proline-stabilized turns. In turn, this could inspire the design and engineering of multicyclic peptides with new structures and benefit the development of novel protein binders and therapeutics.

Design and Synthetic Strategies for Helical Peptides

Abnormal protein-protein interactions (PPIs) are the basis of multiple diseases, and the large and shallow PPI interfaces make the target "undruggable" for traditional small molecules. Peptides, emerging as a new therapeutic modality, can efficiently mimic PPIs with their large scaffolds. Natural peptides are flexible and usually have poor serum stability and cell permeability, features that limit their further biological applications. To satisfy the clinical application of peptide inhibitors, many strategies have been developed to constrain peptides in their bioactive conformation. In this report, we describe several classic methods used to constrain peptides into a fixed secondary structure which could significantly improve their biophysical properties.

Autophagy inducing cyclic peptides constructed by methionine alkylation

Peptides that induced autophagy at micromolar concentrations with improved proteolytic resistance properties were generated using the facile methionine bis-alkylation method. Notably, a short bicyclic peptide 7f was proven to be the most potent one among the designed peptides in regards to autophagy inducing activity. This study facilitated the development of a peptide-based autophagy inducer and demonstrated the potential applications of the methionine alkylation-based macrocyclization method for the diversity-oriented generation of peptide-based autophagy inducers.

Stabilized Peptide HDAC Inhibitors Derived from HDAC1 Substrate H3K56 for the Treatment of Cancer Stem-Like Cells In Vivo

FDA-approved HDAC inhibitors exhibit dose-limiting adverse effects; thus, we sought to improve the therapeutic windows for this class of drugs. In this report, we describe a new class of peptide-based HDAC inhibitors derived from the HDAC1-specific substrate H3K56 with improved nonspecific toxicity compared with traditional small-molecular inhibitors. We showed that our designed peptides exerted superior antiproliferation effects on cancer stem-like cells with minimal toxicity to normal cells compared with the small-molecular inhibitor SAHA, which showed nonspecific toxicity to normal and cancer cells. These peptide inhibitors also inactivated cellular HDAC1 and HDAC6 and disrupted the formation of the HDAC1, LSD1, and CoREST complex. In ovarian teratocarcinoma (PA-1) and testicular embryonic carcinoma (NTERA-2) cell xenograft animal models (5 mice/group, 50 mg/kg, every other day, intraperitoneal injection), these peptides inhibited tumor growth by 80% to 90% with negligible organ (heart, liver, spleen, lung, kidney, brain) lesions. These results represent the first attempt to design chemically stabilized peptide inhibitors to investigate HDAC inhibition in cancer stem-like cells. These novel peptide inhibitors have significantly enhanced therapeutic window and offer promising opportunities for cancer therapy. SIGNIFICANCE: Selective antiproliferative effects of stabilized peptide HDAC inhibitors toward cancer stem-like cells provide a therapeutic alternative that avoids high nonspecific toxicity of current drugs.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/79/8/1769/F1.large.jpg.

Non-reducible disulfide bond replacement implies that disulfide exchange is not required for hepcidin-ferroportin interaction

Previous studies have led to opposing hypotheses about the requirement of intermolecular disulfide exchange in the binding of the iron regulatory peptide hepcidin to its receptor ferroportin. To clarify this issue, we used the diaminodiacid approach to replace the disulfide bonds in hepcidin with non-reducible thioether bonds. Our results implied that disulfide exchange is not required for the interaction between hepcidin and ferroportin. This theory is further supported by our development of biologically active minihepcidins that do not show activity dependence on cysteine.

Tuning the Binding Affinity and Selectivity of Perfluoroaryl-Stapled Peptides by Cysteine-Editing

A growing number of approaches to "staple" α-helical peptides into a bioactive conformation using cysteine cross-linking are emerging. Here, the replacement of l-cysteine with "cysteine analogues" in combinations of different stereochemistry, side chain length and beta-carbon substitution, is explored to examine the influence that the thiol-containing residue(s) has on target protein binding affinity in a well-explored model system, p53-MDM2/MDMX, which is constituted by the interaction of the tumour suppressor protein p53 and proteins MDM2 and MDMX, which regulate p53 activity. In some cases, replacement of one or more l-cysteine residues afforded significant changes in the measured binding affinity and target selectivity of the peptide. Computationally constructed homology models indicate that some modifications, such as incorporating two d-cysteine residues, favourably alter the positions of key functional amino acid side chains, which is likely to cause changes in binding affinity, in agreement with measured surface plasmon resonance data.

HBx-Derived Constrained Peptides Inhibit the Secretion of Hepatitis B Virus Antigens

Hepatitis B virus (HBV) infection is the primary cause of cirrhosis and liver cancer. Protein-protein interactions (PPIs) between HBV x protein (HBx) and its host targets, including Bcl-2, are important for cell death and viral replication. No modulators targeting these PPIs have been reported yet. Here, we developed HBx-derived constrained peptides generated by a facile macrocyclization method by joining two methionine side chains of unprotected peptides with chemoselective alkylating linkers. The resulting constrained peptides with improved cell permeability and binding affinity were effective anti-HBV modulators by blocking the secretion of viral antigens. This study clearly demonstrated HBx as a potentially important PPI target and the potential application of this efficient peptide macrocyclization strategy for targeting key PPIs.

Recent structural advances in constrained helical peptides

Given the ubiquity of the ⍺-helix in the proteome, there has been much research in developing mimics of ⍺-helices, and most of this study has been toward developing protein-protein interaction inhibitors. A common strategy for mimicking ⍺-helices has been through the use of constrained, helical peptides. The addition of a constraint typically provides for conformational and proteolytic stability and, in some cases, cell permeability. Some of the most well-known strategies included are lactam formation and hydrocarbon "stapling." Beyond those strategies, there have been many recent advances in developing constrained peptides. The purpose of this review is to highlight recent advances in the development of new helix-stabilizing technologies, constraint diversification strategies, tether diversification strategies, and combination strategies that create new bicyclic helical peptides.

Synthesis of Peptide Disulfide-Bond Mimics by Using Fully Orthogonally Protected Diaminodiacids

A new strategy was developed for the synthesis of peptide disulfide-bond mimics using fully orthogonally protected diaminodiacids. This method overcomes the previous problems of heavy-metal contamination and poor compatibility with Fmoc chemistry and provides a practical avenue for the efficient preparation of peptide disulfide-bond mimics.

Facile Chemoselective Modification of Thio-Ethers Generates Chiral Center-Induced Helical Peptides

A precisely positioned sulfimide chiral center on-tether of a thio-ether tethered peptide determines the peptide secondary structure by chemoselective oxaziridine modification. This method provides a facile way to tune peptides' secondary structures and biophysical properties.

Emerging Methods and Design Principles for Cell-Penetrant Peptides

Biomolecules such as antibodies, proteins, and peptides are important tools for chemical biology and leads for drug development. They have been used to inhibit a variety of extracellular proteins, but accessing intracellular proteins has been much more challenging. In this review, we discuss diverse chemical approaches that have yielded cell-penetrant peptides and identify three distinct strategies: masking backbone amides, guanidinium group patterning, and amphipathic patterning. We summarize a growing number of large data sets, which are starting to reveal more specific design guidelines for each strategy. We also discuss advantages and disadvantages of current methods for quantifying cell penetration. Finally, we provide an overview of best-odds approaches for applying these new methods and design principles to optimize cytosolic penetration for a given bioactive peptide.

Constructing Thioether/Vinyl Sulfide-tethered Helical Peptides Via Photo-induced Thiol-ene/yne Hydrothiolation

Here, we describe a detailed protocol for the preparation of thioether-tethered peptides using on-resin intramolecular/intermolecular thiol-ene hydrothiolation. In addition, this protocol describes the preparation of vinyl-sulfide-tethered peptides using in-solution intramolecular thiol-yne hydrothiolation between amino acids that possess alkene/alkyne side chains and cysteine residues at i, i+4 positions. Linear peptides were synthesized using a standard Fmoc-based solid-phase peptide synthesis (SPPS). Thiol-ene hydrothiolation is carried out using either an intramolecular thio-ene reaction or an intermolecular thio-ene reaction, depending on the peptide length. In this research, an intramolecular thio-ene reaction is carried out in the case of shorter peptides using on-resin deprotection of the trityl groups of cysteine residues following the complete synthesis of the linear peptide. The resin is then set to UV irradiation using photoinitiator 4-methoxyacetophenone (MAP) and 2-hydroxy-1-[4-(2-hydroxyethoxy)-phenyl]-2-methyl-1-propanone (MMP). The intermolecular thiol-ene reaction is carried out by dissolving Fmoc-Cys-OH in an N,N-dimethylformamide (DMF) solvent. This is then reacted with the peptide using the alkene-bearing residue on resin. After that, the macrolactamization is carried out using benzotriazole-1-yl-oxytripyrrolidinophosphonium hexafluorophosphate (PyBop), 1-hydroxybenzotriazole (HoBt), and 4-Methylmorpholine (NMM) as activation reagents on the resin. Following the macrolactamization, the peptide synthesis is continued using standard SPPS. In the case of the thio-yne hydrothiolation, the linear peptide is cleaved from the resin, dried, and subsequently dissolved in degassed DMF. This is then irradiated using UV light with photoinitiator 2,2-dimethoxy-2-phenylacetophenone (DMPA). Following the reaction, DMF is evaporated and the crude residue is precipitated and purified using high-performance liquid chromatography (HPLC). These methods could function to simplify the generation of thioether-tethered cyclic peptides due to the use of the thio-ene/yne click chemistry that possesses superior functional group tolerance and good yield. The introduction of thioether bonds into peptides takes advantage of the nucleophilic nature of cysteine residues and is redox-inert relative to disulfide bonds.

Universal Implementation of a Residue-Specific Force Field Based on CMAP Potentials and Free Energy Decomposition

The coupling between neighboring backbone ϕ and ψ dihedral angles (torsions) has been well appreciated in protein force field development, as in correction map (CMAP) potentials. However, although preferences of backbone torsions are significantly affected by side-chain conformation, there has been no easy way to optimize this coupling. Herein, we prove that the three-dimensional (3D) free energy hypersurface of joint (ϕ, ψ, χ₁) torsions can be decomposed into three separated 2D surfaces. Thus, each of the 2D torsional surfaces can be efficiently and automatically optimized using a CMAP potential. This strategy is then used to reparameterize an AMBER force field such that the resulting χ₁-dependent backbone conformational preference can agree excellently with the reference protein coil library statistics. In various validation simulations (including the folding of seven peptides/proteins, backbone dynamics of three folded proteins, and two intrinsically disordered peptides), the new RSFF2C (residue-specific force field with CMAP potentials) force field gives similar or better performance compared with RSFF2. This strategy can be used to implement our RSFF force fields into a variety of molecular dynamics packages easily.

Tuning peptide self-assembly by an in-tether chiral center

The self-assembly of peptides into ordered nanostructures is important for understanding both peptide molecular interactions and nanotechnological applications. However, because of the complexity and various self-assembling pathways of peptide molecules, design of self-assembling helical peptides with high controllability and tunability is challenging. We report a new self-assembling mode that uses in-tether chiral center-induced helical peptides as a platform for tunable peptide self-assembly with good controllability. It was found that self-assembling behavior was governed by in-tether substitutional groups, where chirality determined the formation of helical structures and aromaticity provided the driving force for self-assembly. Both factors were essential for peptide self-assembly to occur. Experiments and theoretical calculations indicate long-range crystal-like packing in the self-assembly, which was stabilized by a synergy of interpeptide π-π and π-sulfur interactions and hydrogen bond networks. In addition, the self-assembled peptide nanomaterials were demonstrated to be promising candidate materials for applications in biocompatible electrochemical supercapacitors.

Reversible stapling of unprotected peptides via chemoselective methionine bis-alkylation/dealkylation

We have developed a general peptide macrocyclization strategy that involves a facile and chemoselective methionine bis-alkylation/dealkylation process. This method provides a straightforward and easy approach to generate cyclic peptides with tolerances of all amino acids (including Cys), variable loop sizes, and different linkers. The Met bis-alkylation we apply in this strategy yields two additional on-tether positive charges that could assist in the cellular uptake of the peptides. Notably, the bis-alkylated peptide could be reduced to release the original peptide both in vitro and within cellular environments. This strategy provides an intriguing and facile traceless post-peptide-synthesis modification with enhanced cellular uptakes. Peptides constructed with this method could be utilized to zero in on various protein targets or to achieve other goals, such as drug delivery.

Glucuronic acid as a helix-inducing linker in short peptides

A new strategy is demonstrated for making peptides helical, using a carbohydrate to bridge between sidechains at each end of a pentapeptide. CD and NMR spectra establish that both an α-helix and a 3₁₀-helix structure can form depending upon the bridge.

Switching substitution groups on the in-tether chiral centre influences backbone peptides' permeability and target binding affinity

Different substitution groups on the in-tether chiral centre of chirality-induced helical peptides (CIH peptides) showed distinguishable effects on the peptides' cellular uptakes and binding affinities with the estrogen receptor α(ER-α). This study proves that in-tether chiral centres are a valuable modification site for constructing peptide ligands with preferable biophysical properties.

Development of Stabilized Peptide-Based PROTACs against Estrogen Receptor α

Peptide modulators targeting protein-protein interactions (PPIs) exhibit greater potential than small-molecule drugs in several important aspects including facile modification and relative large contact surface area. Stabilized peptides constructed by variable chemistry methods exhibit improved peptide stability and cell permeability compared to that of the linears. Herein, we designed a stabilized peptide-based proteolysis-targeting chimera (PROTAC) targeting estrogen receptor α (ERα) by tethering an N-terminal aspartic acid cross-linked stabilized peptide ERα modulator (TD-PERM) with a pentapeptide that binds the Von Hippel-Lindau (VHL) E3 ubiquitin ligase complex. The resulting heterobifunctional peptide (TD-PROTAC) selectively recruits ERα to the VHL E3 ligase complex, leading to the degradation of ERα in a proteasome-dependent manner. Compared with the control peptides, TD-PROTAC shows significantly enhanced activities in reducing the transcription of the ERα-downstream genes and inhibiting the proliferation of ERα-positive breast cancer cells. In addition, in vivo experiments indicate that TD-PROTAC leads to tumor regression in the MCF-7 mouse xenograft model. This work is a successful attempt to construct PROTACs based on cell-permeable stabilized peptides, which significantly broadens the chemical space of PROTACs and stabilized peptides.

An in-tether sulfilimine chiral center induces helicity in short peptides

A precisely positioned sulfilimine chiral center in the tether of a stabilized peptide would determine the peptide's secondary structure. Peptide sulfilimines could be prepared by a facile chloramine T oxidation and the two resulting peptide diastereomers showed significant differences in their secondary structures, which were supported by circular dichroism spectroscopy and NMR.

An in-tether sulfilimine chiral center induces β-turn conformation in short peptides

A sulfilimine chiral center in the tether at i, i + 3 positions of short peptides was systematically studied to elucidate the chirality-driven conformational changes. A rare and unexpected type III β-turn structure was induced in short peptides by an in-tether chiral center, supported by circular dichroism spectroscopy, NMR and X-ray crystallography.

N terminal N-methylation modulates chiral centre induced helical (CIH) peptides’ biophysical properties

The effects of N-methylation on CIH peptides’ biophysical properties were systematically studied.

Diastereomeric Right- and Left-Handed Helical Structures with Fourteen (R)-Chiral Centers

The relationship between chiral centers and the helical-screw control of their peptides has already been reported, but it has yet to be elucidated in detail. A chiral four-membered ring α,α-disubstituted α-amino acid with a (R,R)-butane-2,3-diol acetal moiety at the γ-position, but no α-chiral carbon, was synthesized. X-ray crystallographic analysis unambiguously revealed that its homo-chiral heptapeptide formed right-handed (P) and left-handed (M) 3₁₀ -helical structures at a ratio of 1:1. They appeared to be enantiomeric at the peptide backbone, but diastereomeric with fourteen (R)-configuration chiral centers. Conformational analyses of homopeptides in solution also indicated that diastereomeric (P) and (M) helices existed at approximately equal amounts, with a slight preference toward right-handedness, and they quickly interchanged at room temperature. The circumstances of chiral centers are important for the control of their helical-screw direction.

Structural Basis of Inhibition of ERα-Coactivator Interaction by High-Affinity N-Terminus Isoaspartic Acid Tethered Helical Peptides

Direct inhibition of the protein-protein interaction of ERα and its endogenous coactivators with a cell permeable stabilized peptide may offer a novel, promising strategy for combating ERα positive breast cancers. Here, we report the co-crystal structure of a helical peptide stabilized by a N-terminal unnatural cross-linked aspartic acid (TD) in complex with the ERα ligand binding domain (LBD). We designed a series of peptides and peptide 6 that showed direct and high-affinity binding to ERα with selective antiproliferative activity in ERα positive breast cancer cells. The co-crystal structure of the TD-stabilized peptide 6 in complex with ERα LBD further demonstrates that it forms an α helical conformation and directly binds at the coactivator binding site of ERα. Further studies showed that peptide 6_W could potently inhibit cellular ERα's transcriptional activity. This approach demonstrates the potential of TD stabilized peptides to modulate various intracellular protein-protein interactions involved in a range of disorders.

In-Tether Chiral Center Induced Helical Peptide Modulators Target p53-MDM2/MDMX and Inhibit Tumor Growth in Stem-Like Cancer Cell

Inhibition of the interaction between p53 and MDM2/MDMX has attracted significant attention in anticancer therapy development. We designed a series of in-tether chiral center-induced helical stabilized peptides, among which MeR/PhR effectively reactivated p53. The activation of p53 inhibits cell proliferation and induces apoptosis in both the MCF-7 normal tumor cell line and the PA-1 pluripotent cancer cell line with only minimal cellular toxicity towards normal cells or cancer cell lines with p53 mutations. The in vivo bioactivity study of the peptide in the ovarian teratocarcinoma (PA-1) xenograft model showed a tumor growth rate inhibition of 70% with a dosage of 10 mg/kg (one injection every other day). This is the first application of a stabilized peptide modulator targeting stem-like cancer cell both in vitro and in vivo and provides references to cancer stem cell therapy.

New Modalities for Challenging Targets in Drug Discovery

Our ever-increasing understanding of biological systems is providing a range of exciting novel biological targets, whose modulation may enable novel therapeutic options for many diseases. These targets include protein-protein and protein-nucleic acid interactions, which are, however, often refractory to classical small-molecule approaches. Other types of molecules, or modalities, are therefore required to address these targets, which has led several academic research groups and pharmaceutical companies to increasingly use the concept of so-called "new modalities". This Review defines for the first time the scope of this term, which includes novel peptidic scaffolds, oligonucleotides, hybrids, molecular conjugates, as well as new uses of classical small molecules. We provide the most representative examples of these modalities to target large binding surface areas such as those found in protein-protein interactions and for biological processes at the center of cell regulation.

Reversible and Versatile On-Tether Modification of Chiral-Center-Induced Helical Peptides

Modification of the cross-linker of constrained peptides has recently received considerable attention. Here, we present a versatile approach to modifing the cross-linking tether of chiral-center-induced helical (CIH) peptides via the S-alkylation reaction. The alkylation process displayed high conversion efficiency, selectivity, and substrate tolerance. Notably, although on-tether S-alkylation could lead to a pair of peptide epimers, the major alkylated product retained the helical structure of its helical precursor peptide. This S-alkylation was readily reversible under reductive conditions, which provides a simple method for traceless modification. In addition to expanding the chemical space of CIH peptides, this strategy is the first on-tether modification platform with known retention of the peptides' original helicity.

Double quick, double click reversible peptide "stapling"

A versatile, rapid and reversible approach to constrain peptides in a bioactive helical conformation and bearing a functional handle for inhibition of protein–protein interactions is described.

The development of constrained peptides for inhibition of protein–protein interactions is an emerging strategy in chemical biology and drug discovery. This manuscript introduces a versatile, rapid and reversible approach to constrain peptides in a bioactive helical conformation using BID and RNase S peptides as models. Dibromomaleimide is used to constrain BID and RNase S peptide sequence variants bearing cysteine (Cys) or homocysteine (hCys) amino acids spaced at i and i + 4 positions by double substitution. The constraint can be readily removed by displacement of the maleimide using excess thiol. This new constraining methodology results in enhanced α-helical conformation (BID and RNase S peptide) as demonstrated by circular dichroism and molecular dynamics simulations, resistance to proteolysis (BID) as demonstrated by trypsin proteolysis experiments and retained or enhanced potency of inhibition for Bcl-2 family protein–protein interactions (BID), or greater capability to restore the hydrolytic activity of the RNAse S protein (RNase S peptide). Finally, use of a dibromomaleimide functionalized with an alkyne permits further divergent functionalization through alkyne–azide cycloaddition chemistry on the constrained peptide with fluorescein, oligoethylene glycol or biotin groups to facilitate biophysical and cellular analyses. Hence this methodology may extend the scope and accessibility of peptide stapling.

A New Methodology for Incorporating Chiral Linkers into Stapled Peptides

Stapled peptides have arisen as a new class of chemical probe and potential therapeutic agents for modulating protein–protein interactions. Here, we report the first two‐component i,i+7 stapling methodology that makes use of two orthogonal, on‐resin stapling reactions to incorporate linkers bearing a chiral centre into a p53‐derived stapled peptide. Post‐stapling modifications to the chain were performed on‐resin and enabled rapid access to various peptide derivatives from a single staple. The stapled peptides have increased helicity, protease stability and in vitro binding affinities to MDM2 compared to the equivalent unstapled peptide. This approach can be used to generate a library of diverse stapled peptides with different properties starting from a single stapled peptide, with scope for much greater functional diversity than that provided by existing stapling methodologies.

Impact of the amino acid sequence on the conformation of side chain lactam-bridged octapeptides

Synthetic helical peptides are valuable scaffolds for the development of modulators of protein-protein interactions involving helical motifs. Backbone-to-side chain or side chain-to-side chain constraints have been and still are intensively exploited to stabilize short α-helices. Very often, these constraints have been combined with backbone modifications induced by Cα-tetrasubstituted, β-, or γ-amino acids, which facilitate the α-peptide or α/β/γ-peptide adopting an α-helical conformation. In this work, we investigated the helical character of octapeptides that were cyclized by a Lys-Asp-(i,i + 4)-lactam bridge. We started with two sequences extracted from the helix-loop-helix region of the Id proteins, which are inhibitors of cell differentiation during development and in cancer. Nineteen analogs containing the lactam bridge at different positions and displaying different amino acid core triads (i + 1,2,3) as well as outer residues were prepared by solid-phase methodology. Their conformation in water and water/2,2,2-trifluoroethanol mixtures was investigated by circular dichroism (CD) spectroscopy. The cyclopeptides could be grouped in helix-prone and non-helix-prone structures. Both the amino acid core triad (i + 1,2,3) and the pendant residues positively or negatively affected the formation of a helical structure. Computational studies based on the NMR-derived helical structure of a cyclopeptide containing Aib at position (i + 2) of the triad were generally in agreement with the secondary structure propensity of the cyclopeptides observed by CD spectroscopy. In conclusion, the Lys-Asp-(i,i + 4)-lactam bridge may succeed or fail in the stabilization of short helices, depending on the primary structure. Moreover, computational methods may be valuable tools to discriminate helix-prone from non-helix-prone peptide-based macrolactams. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.

An in-tether chiral center modulates the proapoptotic activity of the KLA peptide

We have utilized a novel in-tether chiral center induced helicity strategy (CIH) to develop a potent apoptosis inducer based on apoptotic KLA peptide. For our constructed peptides, the CIH-KLA-(R) epimer exhibited superior cellular uptakes and special mitochondrial targeting when compared with its S counterpart.

A precisely positioned chiral center in an i, i + 7 tether modulates the helicity of the backbone peptide

A chiral center of R absolute configuration at the γ-position to the C-terminal of a 10-membered tether could function to efficiently induce helicity of the backbone peptides.