The impact of N-glycosylation on the properties of the antimicrobial peptide LL-III.

The misuse of antibiotics has led to the emergence of drug-resistant pathogens. Antimicrobial peptides (AMPs) may represent valuable alternative to antibiotics; nevertheless, the easy degradation due to environmental stress and proteolytic enzyme action, limits their use. So far, different strategies have been developed to overcome this drawback. Among them, glycosylation of AMPs represents a promising approach. In this work, we synthesized and characterized the N-glycosilated form of the antimicrobial peptide LL-III (g-LL-III). The N-acetylglucosamine (NAG) was covalently linked to the Asn residue and the interaction of g-LL-III with bacterial model membranes, together with its resistance to proteases, were investigated. Glycosylation did not affect the peptide mechanism of action and its biological activity against both bacteria and eukaryotic cells. Interestingly, a higher resistance to the activity of proteolytic enzymes was achieved. The reported results pave the way for the successful application of AMPs in medicine and biotechnological fields.

Novel Retro-Inverso Peptide Antibiotic Efficiently Released by a Responsive Hydrogel-Based System.

Topical antimicrobial treatments are often ineffective on recalcitrant and resistant skin infections. This necessitates the design of antimicrobials that are less susceptible to resistance mechanisms, as well as the development of appropriate delivery systems. These two issues represent a great challenge for researchers in pharmaceutical and drug discovery fields. Here, we defined the therapeutic properties of a novel peptidomimetic inspired by an antimicrobial sequence encrypted in human apolipoprotein B. The peptidomimetic was found to exhibit antimicrobial and anti-biofilm properties at concentration values ranging from 2.5 to 20 µmol L-1, to be biocompatible toward human skin cell lines, and to protect human keratinocytes from bacterial infections being able to induce a reduction of bacterial units by two or even four orders of magnitude with respect to untreated samples. Based on these promising results, a hyaluronic-acid-based hydrogel was devised to encapsulate and to specifically deliver the selected antimicrobial agent to the site of infection. The developed hydrogel-based system represents a promising, effective therapeutic option by combining the mechanical properties of the hyaluronic acid polymer with the anti-infective activity of the antimicrobial peptidomimetic, thus opening novel perspectives in the treatment of skin infections.

Similarities and differences for membranotropic action of three unnatural antimicrobial peptides.

Previously, we described the design and synthesis of three nine-residue AMPs, P9Nal(SS), P9Trp(SS), and P9Nal(SR), showing high stability in serum and broad spectrum antimicrobial activity. The peptides P9Trp(SS) and P9Nal(SR) differ from P9Nal(SS) for the replacement of the two 2Nal residues with Trp residues and for the replacement of the two Cys (StBu) with Cys (tBu) residues, respectively. These changes led to peptides with a lower hydrophobicity respect to the P9Nal(SS). Interestingly, the three peptides have very similar activity against Gram-negative bacteria. Instead, they exhibit a significant difference towards Gram-positive bacteria, being P9Nal(SS) the most active. In order to evaluate the impact of amino acids substitution on membranotropic activity and rationalize the observed effects in vivo, here, we report the detailed biophysical characterization of the interaction between P9Nal(SR) and P9Trp(SS) and liposomes by combining differential scanning calorimetry, circular dichroism, and fluorescence spectroscopy. The comparison with the results for the previously characterized P9Nal(SS) peptide reveals similarities and differences on the interaction process and perturbation activities. It was found that the three peptides can penetrate at different extent inside the bilayer upon changing their conformation and inducing lipid domains formation, revealing that the formation of lipid domains is fundamental for the activity against Gram-negative bacteria. On the contrary, the dissimilar activity against Gram-positive bacteria well correlate with the different affinity of peptides for the lipoteichoic acid, a component selectively present in the cell wall of Gram-positive bacteria.

Novel human bioactive peptides identified in Apolipoprotein B: Evaluation of their therapeutic potential.

Host defence peptides (HDPs) are short, cationic amphipathic peptides that play a key role in the response to infection and inflammation in all complex life forms. It is increasingly emerging that HDPs generally have a modest direct activity against a broad range of microorganisms, and that their anti-infective properties are mainly due to their ability to modulate the immune response. Here, we report the recombinant production and characterization of two novel HDPs identified in human Apolipoprotein B (residues 887-922) by using a bioinformatics method recently developed by our group. We focused our attention on two variants of the identified HDP, here named r(P)ApoBL and r(P)ApoBS, 38- and 26-residue long, respectively. Both HDPs were found to be endowed with a broad-spectrum antimicrobial activity while they show neither toxic nor haemolytic effects towards eukaryotic cells. Interestingly, both HDPs were found to display a significant anti-biofilm activity, and to act in synergy with either commonly used antibiotics or EDTA. The latter was selected for its ability to affect bacterial outer membrane permeability, and to sensitize bacteria to several antibiotics. Circular dichroism analyses showed that SDS, TFE, and LPS significantly alter r(P)ApoBL conformation, whereas slighter or no significant effects were detected in the case of r(P)ApoBS peptide. Interestingly, both ApoB derived peptides were found to elicit anti-inflammatory effects, being able to mitigate the production of pro-inflammatory interleukin-6 and nitric oxide in LPS induced murine macrophages. It should also be emphasized that r(P)ApoBL peptide was found to play a role in human keratinocytes wound closure in vitro. Altogether, these findings open interesting perspectives on the therapeutic use of the herein identified HDPs.

Femtosecond UV-laser pulses to unveil protein-protein interactions in living cells.

A hallmark to decipher bioprocesses is to characterize protein-protein interactions in living cells. To do this, the development of innovative methodologies, which do not alter proteins and their natural environment, is particularly needed. Here, we report a method (LUCK, Laser UV Cross-linKing) to in vivo cross-link proteins by UV-laser irradiation of living cells. Upon irradiation of HeLa cells under controlled conditions, cross-linked products of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) were detected, whose yield was found to be a linear function of the total irradiation energy. We demonstrated that stable dimers of GAPDH were formed through intersubunit cross-linking, as also observed when the pure protein was irradiated by UV-laser in vitro. We proposed a defined patch of aromatic residues located at the enzyme subunit interface as the cross-linking sites involved in dimer formation. Hence, by this technique, UV-laser is able to photofix protein surfaces that come in direct contact. Due to the ultra-short time scale of UV-laser-induced cross-linking, this technique could be extended to weld even transient protein interactions in their native context.

Redox and electrocatalytic properties of mimochrome VI, a synthetic heme peptide adsorbed on gold.

Mimochrome VI (MC-VI) is a synthetic heme peptide containing a helix-heme-helix sandwich motif designed to reproduce the catalytic activity of heme oxidases. The thermodynamics of Fe(III) to Fe(II) reduction and the kinetics of the electron-transfer process for MC-VI immobilized through hydrophobic interactions on a gold electrode coated with a nonpolar SAM of decane-1-thiol have been determined through cyclic voltammetry. Immobilization slightly affects the reduction potential of MC-VI, which under these conditions electrocatalytically turns over molecular oxygen. This work sets the premise for the exploitation of totally synthetic mimochrome-modified electrode surfaces for clinical and pharmaceutical biosensing.