Stabilisation of a short α‐helical VIP fragment by side chain to side chain cyclisation: a comparison of common cyclisation motifs by circular dichroism

A model octapeptide segment derived from vasoactive intestinal peptide (VIP) was utilised to investigate the effect of several conventional cyclisation methods on the α‐helical conformation in short peptide fragments. Three of the classical macrocyclisation techniques (i.e. lactamisation, ring‐closing metathesis and Huisgen cycloaddition) were applied, and the conformations of the resulting cyclic peptides, as well as their linear precursors, were compared by CD analysis. The visibly higher folding propensity of the triazole‐tethered peptide after azide‐alkyne CuAAC macrocyclisation illustrates that the secondary structure of a short peptide fragment can differ significantly depending on the chemical strategy used to covalently cross‐link side chain residues in a ‘helical’ fragment. Copyright © 2013 European Peptide Society and John Wiley & Sons, Ltd.     

Synthesis and characterization of β‐peptide helices as transmembrane domains in lipid model membranes

Aggregation, orientation and dynamics of transmembrane helices are of relevance for protein function and transmembrane signaling. To explore the interactions of transmembrane helices and the interdependence of peptide structure and lipid composition of the membranes, β‐peptides were explored as model transmembrane domains. Various hydrophobic β‐peptide sequences were synthesized by solid phase peptide synthesis. Conformational analyses of β‐peptide helices were performed in organic solvents (methanol and 2,2,2‐trifluoroethanol) and in large unilamellar liposomes (dimyristoylphosphatidylcholine, dipalmitoylphosphatidylcholine and dioleoylphosphatidylcholine) indicating 12‐ and 14‐helix conformations, depending on β³‐amino acid sequences. The intrinsic tryptophan fluorescence of β³‐homotryptophan units inserted in the center or near the end of the sequence was used to verify the membrane insertion of the β‐peptides. A characteristic blue shift with peripheral β³‐homotryptophan compared with β‐peptides with central tryptophan served as indication for a transmembrane orientation of the β‐peptides within the lipid bilayer. Copyright © 2016 European Peptide Society and John Wiley & Sons, Ltd.     

VCD studies on cyclic peptides assembled from L‐α‐amino acids and a trans‐2‐aminocyclopentane‐ or trans‐2‐aminocyclohexane carboxylic acid

The increasing interest in peptidomimetics of biological relevance prompted us to synthesize a series of cyclic peptides comprising trans‐2‐aminocyclohexane carboxylic acid (Achc) or trans‐2‐aminocyclopentane carboxylic acid (Acpc). NMR experiments in combination with MD calculations were performed to investigate the three‐dimensional structure of the cyclic peptides. These data were compared to the conformational information obtained by electronic circular dichroism (ECD) and vibrational circular dichroism (VCD) spectroscopy. Experimental VCD spectra were compared to theoretical VCD spectra computed quantum chemically at B3LYP/6‐31G(d) density functional theory (DFT) level. The good agreement between the structural features derived from the VCD spectra and the NMR‐based structures underlines the applicability of VCD in studying the conformation of small cyclic peptides. Copyright © 2010 European Peptide Society and John Wiley & Sons, Ltd.     

Vibrational and chiroptical spectroscopic characterization of γ‐turn model cyclic tetrapeptides containing two β‐Ala residues

The optical spectroscopic characterization of γ‐turns in solution is uncertain and their distinction from β‐turns is often difficult. This work reports systematic ECD and vibrational circular dichroism (VCD) spectroscopic studies on γ‐turn model cyclic tetrapeptides cyclo(Ala‐β‐Ala‐Pro‐β‐Ala) ( 1 ), cyclo(Pro‐β‐Ala‐Pro‐β‐Ala) ( 2 ) and cyclo(Ala‐β‐Ala‐Ala‐β‐Ala) ( 3 ). Conformational analysis performed at the 6‐31G(d)/B3LYP level of theory using an adequate PCM solvent model predicted one predominant conformer for 1‐3 , featuring two inverse γ‐turns. The ECD spectra in ACN of 1 and 2 are characterized by a negative n→π* band near 230 nm and a positive π→π* band below 200 nm with a long wavelength shoulder. The ECD spectra in TFE of 1‐3 show similar spectra with blue‐shifted bands. The VCD spectra in ACN‐d₃ of 1 and 2 show a +/?/+/? amide I sign pattern resulting from four uncoupled vibrations in the case of 1 and a sequence of two positive couplets in the case of 2 . A ?/+/+/? amide I VCD pattern was measured for 3 in TFE‐d₂. All three peptides give a positive couplet or couplet‐like feature (+/?) in the amide II region. VCD spectroscopy, in agreement with theoretical calculations revealed that low frequency amide I vibrations (at ～1630 cm^?1 or below) are indicative of a C₇ H‐bonded inverse γ‐turns with Pro in position 2, while γ‐turns encompassing Ala absorb at higher frequency (above 1645 cm^?1). Chirality, 2010. © 2010 Wiley‐Liss, Inc.     

Improved anticancer potency by head‐to‐tail cyclization of short cationic anticancer peptides containing a lipophilic β2,2‐amino acid

We have recently reported a series of synthetic anticancer heptapeptides (H‐KKWβ^2,2WKK‐NH₂) containing a central achiral and lipophilic β^2,2‐amino acid that display low toxicity against non‐malignant cells and high proteolytic stability. In the present study, we have further investigated the effects of increasing the rigidity and amphipathicity of two of our lead heptapeptides by preparing a series of seven to five residue cyclic peptides containing the two most promising β^2,2‐amino acid derivatives as part of the central lipophilic core. The peptides were tested for anticancer activity against human Burkitt's lymphoma (Ramos cells), haemolytic activity against human red blood cells (RBC) and cytotoxicity against healthy human lung fibroblast cells (MRC‐5). The results demonstrated a considerable increase in anticancer potency following head‐to‐tail peptide cyclization, especially for the shortest derivatives lacking a tryptophan residue. High‐resolution NMR studies and molecular dynamics simulations together with an annexin‐V‐FITC and propidium iodide fluorescent assay showed that the peptides had a membrane disruptive mode of action and that the more potent peptides penetrated deeper into the lipid bilayer. The need for new anticancer drugs with novel modes of action is demanding, and development of short cyclic anticancer peptides with an overall rigidified and amphipathic structure is a promising approach to new anticancer agents. Copyright © 2012 European Peptide Society and John Wiley & Sons, Ltd.     

Peptide purification by affinity chromatography based on α‐ketoacyl group chemistry

Significant advances have been achieved in the fields of peptide/protein synthesis, permitting the preparation of large, complex molecules. Shortcomings, however, continue to exist in the area of peptide purification. This paper details some studies we undertook to develop a new strategy for peptide purification based on a reactivity of α‐ketoacyl groups in peptides. The α‐ketoacyl peptide was generated from N^ε‐acyl‐lysyl‐peptide in the solid phase via a transamination reaction using glyoxylic acid and nickel(II) ion. Cleavage of the α‐ketoacyl group with o‐phenylenediamine gave the target peptide in an acceptable yield and purity. We first carried out a careful step‐by‐step optimization of the purification conditions using a model peptide. The strategy was then used in the purification of a transmembrane peptide that could not be effectively purified using a conventional RP‐HPLC system due to the strong hydrophobicity of the peptide and its high tendency to aggregate. Copyright © 2009 European Peptide Society and John Wiley & Sons, Ltd.     

The β‐sheet breakers and π‐stacking

Fibrillation of β‐amyloid is recognized as a key process leading to the development of Alzheimer's disease. Small peptides called β‐sheet breakers were found to inhibit the process of β‐amyloid fibrillation and to dissolve amyloid fibrils in vitro, in vivo, and in cell culture studies [1,2]. The mechanism by which peptide inhibition takes place remains elusive and a detailed model needs to be established. Here, we present new insights into the possible role of consecutive Phe residues, present in the structure of β‐sheet breakers, supported by the results obtained by means of MD simulations. We performed a 30‐ns MD of two β‐sheet breakers: iAβ5 (LPFFD) and iAβ6 (LPFFFD) which have two and three consecutive Phe residues, respectively. We have found that Phe rings in these peptides tend to form stacked conformations. For one of the peptides – iAβ6 – the calculated electrostatic contribution to free energy of one of the conformers with three rings stacked (c2) is significantly lower than that corresponding to the unstacked one (c1), two rings stacked (c0) and second conformer with three rings stacked (c3). This may favor the interaction of the c2 conformer with the target on amyloid fibril. We hypothesize that the mechanism of inhibition of amyloidogenesis by β‐sheet breaker involves competition among π‐stacked Phe residues of the inhibitor and π‐stacking within the β‐amyloid fibril. iAβ6 may be a promising candidate for a lead compound of amyloidogenesis inhibitors. Copyright © 2013 European Peptide Society and John Wiley & Sons, Ltd.     

N‐terminal diproline and charge group effects on the stabilization of helical conformation in alanine‐based short peptides: CD studies with water and methanol as solvent

Protein folding problem remains a formidable challenge as main chain, side chain and solvent interactions remain entangled and have been difficult to resolve. Alanine‐based short peptides are promising models to dissect protein folding initiation and propagation structurally as well as energetically. The effect of N‐terminal diproline and charged side chains is assessed on the stabilization of helical conformation in alanine‐based short peptides using circular dichroism (CD) with water and methanol as solvent. A1 (Ac–Pro–Pro–Ala–Lys–Ala–Lys–Ala–Lys–Ala–NH₂) is designed to assess the effect of N‐terminal homochiral diproline and lysine side chains to induce helical conformation. A2 (Ac–Pro–Pro–Glu–Glu–Ala–Ala–Lys–Lys–Ala–NH₂) and A3 (Ac–d Pro–Pro–Glu–Glu–Ala–Ala–Lys–Lys–Ala–NH₂) with N‐terminal homochiral and heterochiral diproline, respectively, are designed to assess the effect of Glu...Lys (i , i  + 4) salt bridge interactions on the stabilization of helical conformation. The CD spectra of A1 , A2 and A3 in water manifest different amplitudes of the observed polyproline II (PPII) signals, which indicate different conformational distributions of the polypeptide structure. The strong effect of solvent substitution from water to methanol is observed for the peptides, and CD spectra in methanol evidence A2 and A3 as helical folds. Temperature‐dependent CD spectra of A1 and A2 in water depict an isodichroic point reflecting coexistence of two conformations, PPII and β‐strand conformation, which is consistent with the previous studies. The results illuminate the effect of N‐terminal diproline and charged side chains in dictating the preferences for extended‐β, semi‐extended PPII and helical conformation in alanine‐based short peptides. The results of the present study will enhance our understanding on stabilization of helical conformation in short peptides and hence aid in the design of novel peptides with helical structures. Copyright © 2017 European Peptide Society and John Wiley & Sons, Ltd.     

Hexafluoroisopropanol induces self‐assembly of β‐amyloid peptides into highly ordered nanostructures

Deposition of insoluble fibrillar aggregates of β‐amyloid (Aβ) peptides in the brain is a hallmark of Alzheimer's disease. Apart from forming fibrils, these peptides also exist as soluble aggregates. Fibrillar and a variety of nonfibrillar aggregates of Aβ have also been obtained in vitro. Hexafluoroisopropanol (HFIP) has been widely used to dissolve Aβ and other amyloidogenic peptides. In this study, we show that the dissolution of Aβ40, 42, and 43 in HFIP followed by drying results in highly ordered aggregates. Although α‐helical conformation is observed, it is not stable for prolonged periods. Drying after prolonged incubation of Aβ40, 42, and 43 peptides in HFIP leads to structural transition from α‐helical to β‐conformation. The peptides form short fibrous aggregates that further assemble giving rise to highly ordered ring‐like structures. Aβ16–22, a highly amyloidogenic peptide stretch from Aβ, also formed very similar rings when dissolved in HFIP and dried. HFIP could not induce α‐helical conformation in Aβ16–22, and rings were obtained from freshly dissolved peptide. The rings formed by Aβ40, 42, 43, and Aβ16–22 are composed of the peptides in β‐conformation and cause enhancement in thioflavin T fluorescence, suggesting that the molecular architecture of these structures is amyloid‐like. Our results clearly indicate that dissolution of Aβ40, 42 and 43 and the amyloidogenic fragment Aβ16–22 in HFIP results in the formation of annular amyloid‐like structures. Copyright © 2012 European Peptide Society and John Wiley & Sons, Ltd.     

Secondary structure of cell‐penetrating peptides during interaction with fungal cells

Cell‐penetrating peptides (CPPs) are peptides that cross cell membranes, either alone or while carrying molecular cargo. Although their interactions with mammalian cells have been widely studied, much less is known about their interactions with fungal cells, particularly at the biophysical level. We analyzed the interactions of seven CPPs (penetratin, Pep‐1, MPG, pVEC, TP‐10, MAP, and cecropin B) with the fungal pathogen Candida albicans using experiments and molecular simulations. Circular dichroism (CD) of the peptides revealed a structural transition from a random coil or weak helix to an α‐helix occurs for all peptides when the solvent is changed from aqueous to hydrophobic. However, CD performed in the presence of C. albicans cells showed that proximity to the cell membrane is not necessarily sufficient to induce this structural transition, as penetratin, Pep‐1, and MPG did not display a structural shift in the presence of cells. Monte Carlo simulations were performed to further probe the molecular‐level interaction with the cell membrane, and these simulations suggested that pVEC, TP‐10, MAP, and cecropin B strongly penetrate into the hydrophobic domain of the membrane lipid bilayer, inducing a transition to an α‐helical conformation. In contrast, penetratin, Pep‐1 and MPG remained in the hydrophilic region without a shift in conformation. The experimental data and MC simulations combine to explain how peptide structure affects their interaction with cells and their mechanism of translocation into cells (direct translocation vs. endocytosis). Our work also highlights the utility of combining biophysical experiments, biological experiments, and molecular modeling to understand biological phenomena.     

Cationic oligopeptides with the repeating sequence L‐lysyl‐L‐alanyl‐L‐alanine: conformational and thermal stability study using optical spectroscopic methods

The infrared (IR), vibrational circular dichroism (VCD), and electronic circular dichroism (ECD) spectra of short cationic sequential peptides (L ‐Lys‐L ‐Ala‐L ‐Ala)_n (n = 1, 2, and 3) were measured over a range of temperatures (20–90 °C) in aqueous solution at near‐neutral pH values in order to investigate their solution conformations and thermally induced conformational changes. VCD spectra of all three oligopeptides measured in the amide I′ region indicate the presence of extended helical polyproline II (PPII)‐like conformation at room temperature. UV‐ECD spectra confirmed this conclusion. Thus, the oligopeptides adopt a PPII‐like conformation, independent of the length of the peptide chain. However, the optimized dihedral angles ? and ψ are within the range ?82 to ?107° and 143–154°, respectively, and differ from the canonical PPII values. At elevated temperatures, the observed intensity and bandshape variations in the VCD and ECD spectra show that the PPII‐like conformation of the Lys‐Ala‐Ala sequence is still preferred, being in equilibrium with an unordered conformer at near‐neutral pH values within the range of temperatures from 20 to 90 °C. This finding was obtained from analysis of the temperature‐dependent spectra using the singular value decomposition method. The study presents KAA‐containing oligopeptides as conformationally stable models of biologically important cationic peptides and proteins. Copyright © 2009 European Peptide Society and John Wiley & Sons, Ltd.     

De novo design,synthesis and solution conformational study of two didehydroundecapeptides: effect of nature and number of amino acids interspersed between Phe residues

De novo design of peptides and proteins has recently surfaced as an approach for investigating protein structure and function. This approach vitally tests our knowledge of protein folding and function, while also laying the groundwork for the fabrication of proteins with properties not precedented in nature. The success relies heavily on the ability to design relatively short peptides that can espouse stable secondary structures. To this end, substitution with α,β‐didehydroamino acids, especially α,β‐didehydrophenylalanine (Δ^zPhe), comes in use for spawning well‐defined structural motifs. Introduction of ΔPhe induces β‐bends in small and 3₁₀‐helices in longer peptide sequences. The present work aims to investigate the effect of nature and the number of amino acids interspersed between two ΔPhe residues in two model undecapeptides, Ac‐Gly‐Ala‐ΔPhe‐Ile‐Val‐ΔPhe‐Ile‐Val‐ΔPhe‐Ala‐Gly‐NH₂ (I) and Boc‐Val‐ΔPhe‐Phe‐Ala‐Phe‐ΔPhe‐Phe‐Leu‐Ala‐ΔPhe‐Gly‐OMe (II). Peptide I was synthesized using solid‐phase chemistry and characterized using circular dichroism spectroscopy. Peptide II was synthesized using solution‐phase chemistry and characterized using circular dichroism and nuclear magnetic resonance spectroscopy. Peptide I was designed to examine the effect of incorporating β‐strand‐favoring residues like valine and isoleucine as spacers between two ΔPhe residues on the final conformation of the resulting peptide. Circular dichroism studies on this peptide have shown the existence of a 3₁₀‐helical conformation. Peptide II possesses three amino acids as spacers between ΔPhe residues and has been reported to adopt a mixed 3₁₀/α‐helical conformation using circular dichroism and nuclear magnetic resonance spectroscopy studies. Copyright © 2011 European Peptide Society and John Wiley & Sons, Ltd.     

Bacterial β‐Aminopeptidases: Structural Insights and Applications for Biocatalysis

β‐Aminopeptidases comprise a class of enzymes with functional and structural similarities. All members of the β‐aminopeptidases described to date were isolated from bacterial sources. Uniquely, they catalyze the hydrolysis of β³‐ and/or β²‐amino acid residues from amides and peptides that are otherwise considered proteolytically stable. Due to this unusual reactivity with β‐peptide substrates, β‐aminopeptidases have potential to be used as biocatalysts for β‐peptide synthesis and for the resolution of enantiomerically pure β‐amino acids from racemic substrate mixtures. β‐Aminopeptidases are formed from an inactive precursor by posttranslational autoproteolytic cleavage, exposing the catalytic nucleophile at the N‐terminus of the newly formed β‐polypeptide chain. Such an activation step is a characteristic trait of enzymes of the N‐terminal nucleophile (Ntn) hydrolase superfamily. However, classical Ntn hydrolases and β‐aminopeptidases differ by the fold of their catalytic cores and are hence likely to originate from distinct evolutionary ancestors. In this contribution, we review the existing literature on β‐aminopeptidases, including biochemical and functional studies, as well as structural investigations that recently allowed insights into the catalytic mechanisms of precursor processing and β‐peptide conversion.     

Folding thermodynamics of β‐hairpins studied by replica‐exchange molecular dynamics simulations

We study the differences in folding stability of β‐hairpin peptides, including GB1 hairpin and a point mutant GB1 K10G, as well as tryptophan zippers (TrpZips): TrpZip1, TrpZip2, TrpZip3‐1, and TrpZip4. By performing replica‐exchange molecular dynamics simulations with Amber03* force field (a modified version of Amber ff03) in explicit solvent, we observe ab initio folding of all the peptides except TrpZip3‐1, which is experimentally known to be the least stable among the peptides studied here. By calculating the free energies of unfolding of the peptides at room temperature and folding midpoint temperatures for thermal unfolding of peptides, we find that TrpZip4 and GB1 K10G peptides are the most stable β‐hairpins followed by TrpZip1, GB1, and TrpZip2 in the given order. Hence, the proposed K10G mutation of GB1 peptide results in enhanced stability compared to wild‐type GB1. An important goal of our study is to test whether simulations with Amber 03* model can reproduce experimentally predicted folding stability differences between these peptides. While the stabilities of GB1 and TrpZip1 yield close agreement with experiment, TrpZip2 is found to be less stable than predicted by experiment. However, as heterogenous folding of TrpZip2 may yield divergent thermodynamic parameters by different spectroscopic methods, mismatching of results with previous experimental values are not conclusive of model shortcomings. For most of the cases, molecular simulations with Amber03* can successfully reproduce experimentally known differences between the mutated peptides, further highlighting the predictive capabilities of current state‐of‐the‐art all‐atom protein force fields. Proteins 2015; 83:1307–1315. © 2015 Wiley Periodicals, Inc.     

FTIR spectroscopic studies on aggregation process of the β‐amyloid 11–28 fragment and its variants

Aggregation of Aβ peptides is a seminal event in Alzheimer's disease. Detailed understanding of the Aβ assembly process would facilitate the targeting and design of fibrillogenesis inhibitors. Here, conformational studies using FTIR spectroscopy are presented. As a model peptide, the 11–28 fragment of Aβ was used. This model peptide is known to contain the core region responsible for Aβ aggregation. The structural behavior of the peptide during aggregation provoked by the addition of water to Aβ(11–28) solution in hexafluoroisopropanol was compared with the properties of its variants corresponding to natural, clinically relevant mutants at positions 21–23 (A21G, E22K, E22G, E22Q and D23N). The results showed that the aggregation of the peptides proceeds via a helical intermediate, and it is possible that the formation of α‐helical structures is preceded by creation of 3₁₀‐helix/3₁₀‐turn structures. Copyright © 2008 European Peptide Society and John Wiley & Sons, Ltd.     

N‐terminal truncated pyroglutamyl β amyloid peptide Aβpy3‐42 shows a faster aggregation kinetics than the full‐length Aβ1‐42

We tested directly the differences in the aggregation kinetics of three important β amyloid peptides, the full‐length Aβ1‐42, and the two N‐terminal truncated and pyroglutamil modified Aβpy3‐42 and Aβpy11‐42 found in different relative concentrations in the brains in normal aging and in Alzheimer disease. By following the circular dichroism signal and the ThT fluorescence of the solution in phosphate buffer, we found substantially faster aggregation kinetics for Aβpy3‐42. This behavior is due to the particular sequence of this peptide, which is also responsible for the specific oligomeric aggregation states, found by TEM, during the fibrillization process, which are very different from those of Aβ1‐42, more prone to fibril formation. In addition, Aβpy3‐42 is found here to have an inhibitory effect on Aβ1‐42 fibrillogenesis, coherently with its known greater infective power. This is an indication of the important role of this peptide in the aggregation process of β‐peptides in Alzheimer disease. © 2009 Wiley Periodicals, Inc. Biopolymers 91: 861–873, 2009. This article was originally published online as an accepted preprint. The “Published Online“ date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com     

Engineered cystine knot peptides that bind αvβ3, αvβ5, and α5β1 integrins with low‐nanomolar affinity

There is a critical need for compounds that target cell surface integrin receptors for applications in cancer therapy and diagnosis. We used directed evolution to engineer the Ecballium elaterium trypsin inhibitor (EETI‐II), a knottin peptide from the squash family of protease inhibitors, as a new class of integrin‐binding agents. We generated yeast‐displayed libraries of EETI‐II by substituting its 6‐amino acid trypsin binding loop with 11‐amino acid loops containing the Arg‐Gly‐Asp integrin binding motif and randomized flanking residues. These libraries were screened in a high‐throughput manner by fluorescence‐activated cell sorting to identify mutants that bound to α_vβ₃ integrin. Select peptides were synthesized and were shown to compete for natural ligand binding to integrin receptors expressed on the surface of U87MG glioblastoma cells with half‐maximal inhibitory concentration values of 10–30 nM. Receptor specificity assays demonstrated that engineered knottin peptides bind to both α_vβ₃ and α_vβ₅ integrins with high affinity. Interestingly, we also discovered a peptide that binds with high affinity to α_vβ₃, α_vβ₅, and α₅β₁ integrins. This finding has important clinical implications because all three of these receptors can be coexpressed on tumors. In addition, we showed that engineered knottin peptides inhibit tumor cell adhesion to the extracellular matrix protein vitronectin, and in some cases fibronectin, depending on their integrin binding specificity. Collectively, these data validate EETI‐II as a scaffold for protein engineering, and highlight the development of unique integrin‐binding peptides with potential for translational applications in cancer. Proteins 2009. © 2009 Wiley‐Liss, Inc.     

Nanostructures from the self‐assembly of α‐helical peptide amphiphiles

Self‐assembly of PAs composed of palmitic acid and several repeated heptad peptide sequences, C₁₅H₃₁CO‐(IEEYTKK)_n‐NH₂ (n = 1–4, represented by PA1–PA4), was investigated systematically. The secondary structures of the PAs were characterized by CD. PA3 and PA4 (n = 3 and 4, respectively) showed an α‐helical structure, whereas PA1 and PA2 (n = 1 and 2, respectively) did not display an α‐helical conformations under the tested conditions. The morphology of the self‐assembled peptides in aqueous medium was studied by transmission electron microscopy. As the number of heptad repeats in the PAs increased, the nanostructure of the self‐assembled peptides changed from nanofibers to nanovesicles. Changes of the secondary structures and the self‐assembly morphologies of PA3 and PA4 in aqueous medium with various cations were also studied. The critical micelle concentrations were determined using a pyrene fluorescence probe. In conclusion, this method may be used to design new peptide nanomaterials. Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.     

Effect of agitation on the peptide fibrillization: Alzheimer's amyloid‐β peptide 1‐42 but not amylin and insulin fibrils can grow under quiescent conditions

Many peptides and proteins can form fibrillar aggregates in vitro, but only a limited number of them are forming pathological amyloid structures in vivo. We studied the fibrillization of four peptides – Alzheimer's amyloid‐β (Aβ) 1‐40 and 1‐42, amylin and insulin. In all cases, intensive mechanical agitation of the solution initiated fast fibrillization. However, when the mixing was stopped during the fibril growth phase, the fibrillization of amylin and insulin was practically stopped, and the rate for Aβ₄₀ substantially decreased, whereas the fibrillization of Aβ₄₂ peptide continued to proceed with almost the same rate as in the agitated conditions. The reason for the different sensitivity of the in vitro fibrillization of these peptides towards agitation in the fibril growth phase remains elusive. Copyright © 2013 European Peptide Society and John Wiley & Sons, Ltd.     

Investigating hydrophobic ligand–receptor interactions in parathyroid hormone receptor using peptide probes

With an increasing number of new chemical entities entering clinical studies, and an increasing share of the market, peptides and peptidomimetics constitute one of the most promising classes of therapeutics. The success of synthetic peptides as therapeutics relies on the lead optimization step in which the lead candidates are modified to improve drug‐like properties of peptides related to potency, pharmacokinetics, solubility, and stability, among others. Peptidomimetics based on the N‐terminal stretch of the first 11 amino acids of the PTH have been investigated as potential lead compounds for the treatment of osteoporosis. On the basis of a peptide reported in the literature, referred to here as the Parent Peptide (H‐Aib‐Val‐Aib‐Glu‐Ile‐Gln‐Leu‐Nle‐His‐Gln‐Har‐NH₂), we conducted systematic SAR analyses to investigate the effects of altering peptide hydrophobicity on PTH receptor functional potency as measured by the cAMP (cyclic adenosine monophosphate) accumulation and β‐arrestin recruitment assays. Among hydrophobic residues, we found that the Val2 position shows the least flexibility in terms of the SAR studies, whereas the Leu7 position appeared to be most flexible. Through circular dichroism and nuclear magnetic resonance spectroscopy studies, we were able to establish that changes in hydrophobic residues significantly change the extent of peptide helicity and that the helical character correlates well with receptor agonist activity. Here, we report several novel PTH 1–11 peptidomimetics that show comparable or enhanced potency to stimulate G_s‐signaling over β‐arrestin recruitment as compared with such properties of PTH 1–34 and the Parent Peptide. Copyright © 2013 European Peptide Society and John Wiley & Sons, Ltd.