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Hybrid associates formed between peptide assemblies and fluorophores are attractive mainly because of their unique properties for biomedical applications. Recently, we demonstrated that the production of reactive oxygen species (ROS) by hypericin and their stability in excited states are enhanced upon conjugation with l,l-diphenylalanine microtubes (FF-MNTs). Although the detailed mechanisms responsible for improving the photophysical properties of ROS remain unclear, tentative hypotheses have suggested that the driving force is the growth of overall dipolar moments ascribed either to coupling between aligned H₂O dipoles within the ordered structures or to the organization of hypericin molecules on peptide interfaces. To provide new insights on ROS activity in hypericin/FF-MNTs hybrids and further explore the role of water in this respect, we present results obtained from investigations on the behavior of these complexes organized into different crystalline arrangements. Specifically, we monitored and compared the photophysical performance of hypericin bound to FF-MNTs with peptides organized in both hexagonal (water-rich) and orthorhombic (water-free) symmetries. From a theoretical perspective, we present the results of new molecular dynamics simulations that highlight the distinct hypericin/peptide interaction at the interface of FF-MNTs for the different symmetries. As a conclusion, we propose that although water enhances photophysical properties, the organization induced by peptide structures and the availability of a hydrophobic environment surrounding the hypericin/peptide interface are paramount to optimizing ROS generation. The findings presented here provide useful basic research insights for designing peptide/fluorophore complexes with outstanding technological potential. Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.

The generation of reactive oxygen species (ROS) by hypericin has been found to be significantly improved upon association with l,l-diphenylalanine microtubes. The photophysical performance of these hybrids was investigated for assemblies organized into both hexagonal (water-rich) and orthorhombic (water-free) symmetries. We have found that organization induced by peptide structures and availability of a hydrophobic micro-environment surrounding the hypericin/peptide interface are paramount to optimizing ROS generation.

Interactions between peptides are relevant from a biomedical point of view, in particular for the role played by their aggregates in different important pathologies, and also because peptide aggregates represent promising scaffolds for innovative materials.

In the present article, the aggregation properties of the homo-peptides formed by α-aminoisobutyric acid (U) residues are discussed. The peptides investigated have chain lengths between six and 15 residues and comprise benzyl and naphthyl groups at the N- and C-termini, respectively. Spectroscopic experiments and molecular dynamics simulations show that the shortest homo-peptide, constituted by six U, does not exhibit any tendency to aggregate under the conditions examined. On the other hand, the homologous peptide with 15 U forms very stable and compact aggregates in 70/30_(v/v) methanol/water solution. Atomic force microscopy images indicate that these aggregates promote formation of long fibrils once they are deposited on a mica surface. The aggregation phenomenon is mainly due to hydrophobic interactions occurring between very stable helical structures, and the aromatic groups in the peptides seem to play a minor role. Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.

The aggregation properties of Aib homo-peptides have been analyzed by means of computational and experimental techniques. Our findings reveal that the longer homolog of the series, (Aib)₁₅, forms stable aggregates in water/methanol solutions and fibers when dried on mica surface. (Aib)₆, on the contrary, does not show any tendency to aggregate because of its intrinsic higher flexibility in the investigated conditions. During the molecular dynamics simulations (tens of nanoseconds long) of (Aib)₆, both P- and M-helices were populated.

Celiac disease (CD) is an autoimmune mediated disease with complex and multifactorial etiology. Gluten intake triggers a composite immune response involving T-cells and B-cells and leading to the secretion of autoantibodies if a genetic predisposition is present. Untreated CD patients show high levels of circulating autoantibodies directed to different auto-antigens present in the intestinal mucosa. The most important auto-antigen is the endomysial enzyme tissue transglutaminase (tTG). Both IgA and IgG antibody isotypes to tTG are known, but only the IgA antibodies demonstrate the highest disease specificity and thus are considered disease biomarkers. Because the pathogenicity and exact tTG binding properties of these autoantibodies are still unclear, the characterization of tTG antigenic domains is a crucial step in understanding CD onset and the autoimmune pathogenesis. Overlapping peptide libraries can be used for epitope mapping of selected protein portions to determine antigenic fragments contributing to the immunological activity and possibly develop innovative peptide-based tools with high specificity and sensitivity for CD. We performed an epitope mapping study to characterize putative linear auto-antigenic epitopes present in the tTG N-terminal portion (1–230). A library of 23 overlapping peptides spanning tTG(1–230) was generated by Fmoc/tBu solid-phase peptide synthesis and screened by immunoenzymatic assays employing patients' sera. The results indicate that four synthetic peptides, that is, Ac-tTG(1–15)-NH₂, Ac-tTG(41–55)-NH₂, Ac-tTG(51–65)-NH₂, and Ac-tTG(151–165)-NH₂, are recognized by IgA autoantibodies circulating in CD patients' sera. These results offer important insight on the nature of the antigen-antibody interaction. Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.

Mapping of the tissue transglutaminase N-terminal portion (1–230) identified putative linear auto-antigenic epitopes. A library of 23 overlapping peptides was generated by Fmoc/tBu solid-phase peptide synthesis and screened by immunoenzymatic assays. Four peptides are recognized as linear epitopes by IgA autoantibodies circulating in celiac disease patients' sera.

Proteasome is a ‘proteolytic factory’ that constitutes an essential part of the ubiquitin-proteasome pathway. The involvement of proteasome in regulation of all major aspects of cellular physiology makes it an attractive drug target. So far, only inhibitors of the proteasome entered the clinic as anti-cancer drugs. However, proteasome regulators may also be useful for treatment of inflammatory and neurodegenerative diseases. We established in our previous studies that the peptide Tat2, comprising the basic domain of HIV-1 Tat protein: R⁴⁹KKRRQRR⁵⁶, supplemented with Q⁶⁶DPI⁶⁹ fragment, inhibits the 20S proteasome in a noncompetitive manner. Mechanism of Tat2 likely involves allosteric regulation because it competes with the proteasome natural 11S activator for binding to the enzyme noncatalytic subunits. In this study, we performed alanine walking coupled with biological activity measurements and FTIR and CD spectroscopy to dissect contribution of a charge and conformation of Tat2 to its capability to influence peptidase activity of the proteasome. In solution, Tat2 and most of its analogs with a single Ala substitution preferentially adopted a conformation containing PPII/turn structural motifs. Replacing either Asp10 or two or more adjacent Arg/Lys residues induced a random coil conformation, probably by disrupting ionic interactions responsible for stabilization of the peptides ordered structure. The random coil Tat2 analogs lost their capability to activate the latent 20S proteasome. In contrast, inhibitory properties of the peptides more significantly depended on their positive charge. The data provide valuable clues for the future optimization of the Tat2-based proteasome regulators. Copyright © 2014 European Peptide Society and John Wiley & Sons, Ltd.

Ala scan studies of Tat2 peptide, a noncompetitive inhibitor of human SDS-activated 20S proteasome and a weak activator of the latent 20S, revealed that different peptide features are responsible for its stimulating and inhibitory activity toward the proteasome chymotrypsin-like peptidase. While for stimulating capacity preservation of the PPII/turn conformation seems to play an important role, inhibitory capacity depends rather on the positive charge.