Alamethicin self-assembling in lipid membranes: concentration dependence from pulsed EPR of spin labels

The antimicrobial action of the peptide antibiotic alamethicin (Alm) is commonly related to peptide self-assembling resulting in the formation of voltage-dependent channels in bacterial membranes, which induces ion permeation. To obtain a deeper insight into the mechanism of channel formation, it is useful to know the dependence of self-assembling on peptide concentration. With this aim, we studied Alm F50/5 spin-labeled analogs in a model 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) membrane, for peptide-to-lipid (P/L) ratios varying between 1/1500 and 1/100. Pulsed electron-electron double resonance (PELDOR) spectroscopy reveals that even at the lowest concentration investigated, the Alm molecules assemble into dimers. Moreover, under these conditions, electron spin echo envelope modulation (ESEEM) spectroscopy of D2O-hydrated membranes shows an abrupt change from the in-plane to the trans-membrane orientation of the peptide. Therefore, we hypothesize that dimer formation and peptide reorientation are concurrent processes and represent the initial step of peptide self-assembling. By increasing peptide concentration, higher oligomers are formed. A simple kinetic model of equilibrium among monomers, dimers, and pentamers allows for satisfactorily describing the experimental PELDOR data. The inter-label distances in the oligomers obtained from PELDOR experiments become better resolved with increasing P/L ratio, thus suggesting that the supramolecular organization of the higher-order oligomers becomes more defined

Hydrogen-bond-assisted, concentration-dependent molecular dimerization of ferrocenyl hydantoins

The synthesis and characterization of the ferrocenyl methylhydantoin 5-ferrocenyl-5-methylimidazolidine-2,4-dione, efficiently prepared through a Bucherer-Bergs reaction, and its derivatives carrying tert-butoxycarbonyl (Boc) protecting groups, namely 1,3-bis(tert-butoxycarbonyl)-5-ferrocenyl-S-methylirnidazolidine-2,4-dione and 1-(tert-butoxycarbonyl)-5-ferrocenyl-5-methylimidazolidine-2,4-dione, are reported. X-ray diffraction and ESI-mass spectrometry analyses of the ferrocenyl methylhydantoin revealed the presence of C=O center dot center dot center dot H-N intermolecularly hydrogen-bonded dimers. The mono-Boc derivative formed a hydrogen-bonded dimer in solution, as confirmed by H-1 NMR, FT-IR, and cyclic voltammetry experiments at different concentrations in CDCl3 or CHCl3

correction an epr study of ampullosporin a a medium length peptaibiotic in bicelles and vesicles

Correction for 'An EPR study of ampullosporin A, a medium-length peptaibiotic, in bicelles and vesicles' by Marco Bortolus et al., Phys. Chem. Chem. Phys., 2016, 18, 749–760

Conformationally Constrained Peptides with High Affinity to the Vascular Endothelial Growth Factor

The design of efficient vascular endothelial growth factor (VEGF) inhibitors is a high-priority research area aimed at the treatment of pathological angiogenesis. Among other compounds, v114* has been identified as a potent VEGF-binding peptide. In order to improve the affinity to VEGF, we built a conformational constrain in its structure. To this aim, C-alpha-tetrasubstituted amino acid Aib was introduced into the N-terminal tail, peptide loop, or C-terminal helix. NMR studies confirmed the stabilization of the helical conformation in proximity to the Aib residue. We found that the induction of the N-terminal helical structure or stabilization of the C-terminal helix can noticeably increase the peptide affinity to the VEGF. These peptides efficiently inhibited VEGF-stimulated cell proliferation as well. The insertion of the non-proteinogenic Aib residue significantly enhanced the stability of the peptides in the vitreous environment. Thus, these Aib-containing peptides are promising candidates for the design of VEGF inhibitors with improved properties.Peer reviewe

Covalent Graft of Lipopeptides and Peptide Dendrimers to Cellulose Fibers

Introduction: Bacterial proliferation in health environments may lead to the development of specific pathologies, but can be highly dangerous under particular conditions, such as during chemotherapy. To limit the spread of infections, it is helpful to use gauzes and clothing containing antibacterial agents. As cotton tissues are widespread in health care environments, in this contribution we report the preparation of cellulose fibers characterized by the covalent attachment of lipopeptides as possible antimicrobial agents. Aim: To covalently link peptides to cotton samples and characterize them. Peptides are expected to preserve the features of the fabrics even after repeated washing and use. Peptides are well tolerated by the human body and do not induce resistance in bacteria. Materials and Methods: A commercially available cotton tissue (specific weight of 150 g/m2, 30 Tex yarn fineness, fabric density of 270/230 threads/10 cm in the warp and weft) was washed with alkali and bleached and died. A piece of this tissue was accurately weighed, washed with methanol (MeOH) and N,N-dimethylformamide (DMF), and air-dried. Upon incubation with epibromohydrin, followed by treatment with Fmoc-NH-CH2CH2-NH2 and Fmoc removal, the peptides were synthesized by incorporating one amino acid at a time, beginning with the formation of an amide bond with the free NH2 of 1,2\u2013diaminoethane. We also linked to the fibers a few peptide dendrimers, because the mechanism of action of these peptides often requires the formation of clusters. We prepared and characterized seven peptide-cotton samples. Results: The new peptide-cotton conjugates were characterized by means of FT-IR spectroscopy and X-ray Photoelectron Spectroscopy (XPS). This latter technique allows for discriminating among different amino acids and thus different peptide-cotton samples. Some samples maintain a pretty good whiteness degree even after peptide functionalization. Interestingly, these samples also display encouraging activities against a Gram positive strain. Conclusions: Potentially antimicrobial lipopeptides can be covalently linked to cotton fabrics, step-by-step. It is also possible to build on the cotton Lys-based dendrimers. XPS is a useful technique to discriminate among different types of nitrogen. Two samples displaying some antibacterial potency did also preserve their whiteness index

A study of a C Α, Β -didehydroalanine homo-oligopeptide series in the solid-state by 13 C cross-polarization magic angle spinning NMR

The fully extended peptide conformation (2.0 5 -helix) has been investigated for the first time in the solid-state by 13 C cross-polarization magic angle spinning NMR. The compounds examined are members of a terminally protected, homo-oligopeptide series (from monomer through hexamer) based on C Α, Β -didehydroalanine. Copyright © 2004 European Peptide Society and John Wiley & Sons, Ltd.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/35198/1/551_ftp.pd

Fluoro-Aryl Substituted α,β2,3-Peptides in the Development of Foldameric Antiparallel β-Sheets: A Conformational Study

\u3b1,\u3b22,3 -Disteroisomeric foldamers of general formula Boc(S-Ala-\u3b2-2R,3R-Fpg)n OMe or Boc(S-Ala-\u3b2-2S,3S-Fpg)n OMe were prepared from both enantiomers of syn H-2-(2-F-Phe)-h-PheGly-OH (named \u3b2-Fpg) and S-alanine. Our peptides show two appealing features for biomedical applications: the presence of fluorine, attractive for non-covalent interactions, and aryl groups, crucial for \u3c0-stacking. A conformational study was performed, using IR, NMR and computational studies of diastereoisomeric tetra- and hexapeptides containing the \u3b22,3-amino acid in the R,R- and S,S-stereochemistry, respectively. We found that the stability of peptide conformation is dependent on the stereochemistry of the \u3b2-amino acid. Combining S-Ala with \u3b2-2R,3R-Fpg, a stable extended \u3b2-strand conformation was obtained. Furthermore, \u3b2-2R,3R-Fpg containing hexapeptide self-assembles to form antiparallel \u3b2-sheet structure stabilized by intermolecular H-bonds and \u3c0,\u3c0-interactions. These features make peptides containing the \u3b22,3-fluoro amino acid very appealing for the development of bioactive proteolytically stable foldameric \u3b2-sheets as modulators of protein-protein interaction (PPI)

Peptide delta-turn: Literature survey and recent progress

Among the various types of a-peptide folding motifs, delta-turn, which requires a central cis-amide disposition, has been one of the least extensively investigated. In particular, this main-chain reversal topology has been studied in-depth neither in linear/cyclic peptides nor in proteins. This Minireview article assembles and critically analyzes relevant data from a literature survey on the d-turn conformation in those compounds. Unpublished results from recent conformational energy calculations and a preliminary solution-state analysis on a small model peptide, currently ongoing in our laboratories, are also briefly outlined.Postprint (published version

Anticancer gold(III) peptidomimetics: from synthesis to in vitro and ex vivo biological evaluation

Five new Au(III)‐peptidodithiocarbamato complexes of the type [AuIIIBr2(dtc‐AA1‐AA2‐OR] (AA1=Sar, L/D‐Pro; AA2=L/D‐Ala, Aib; R=OtBu, TEG), differing in the amino acidic sequence and/or the chiral amino acid configuration, were designed to enhance the tumor selectivity and bioavailability. The gold(III)‐based moiety was functionalized to exploit the targeting properties of the peptidomimetic ligand towards two peptide transporters (namely, PEPT1 and PEPT2), up‐regulated in several tumor cells. The compounds were synthesized and fully characterized, mainly by means of elemental analysis, mono‐ and bidimensional NMR spectroscopy, FT‐IR and UV‐Vis spectrophotometries. The crystal structures of three compounds were also solved by X‐ray diffraction. In vitro cytotoxicity studies using a panel of human tumor cell lines (A549, MCF‐7, A2780, H1975, H460 and A431) showed that the dtc‐Pro‐Aib‐OtBu derivative is very effective, with GI50 values much lower than those of Cisplatin. It was thus selected for evaluating the stability under physiological conditions and possible interaction with serum albumin as well as for PARP‐1 enzyme inhibition assays and preliminary ex vivo toxicity experiments on healthy rat tissues