Enhancing Antimicrobial Peptide Potency through Multivalent Presentation on Coiled-Coil Nanofibrils.

Antibiotic-resistant microbes have become a global health threat. New delivery systems that enhance the efficacy of antibiotics and/or overcome the resistances can help combat them. In this context, we present FF03, a fibril-forming α-helical coiled-coil peptide that functions as an efficient scaffold for the multivalent presentation of the weakly cationic antimicrobial peptide (AMP) IN4. The resulting IN4-decorated FF03 coiled-coil fibrils (FF03 + IN4) are nonhemolytic and noncytotoxic and show enhanced antimicrobial activity relative to unconjugated IN4 and standard antibiotics against several bacterial strains. Scanning electron microscopy analysis shows that FF03 + IN4 nanofibers disrupt methicillin-resistant Staphylococcus aureus membranes, indicating a surface-level mode of action. Furthermore, transmission electron microscopy and circular dichroism studies indicate that decoration of the FF03 scaffold with IN4 does not alter the secondary-structure propensity or fibril-forming properties of FF03. Thus, the approach reported herein provides a new peptidic scaffold for the multivalent presentation of AMPs to obtain nonhemolytic and noncytotoxic antimicrobial systems with improved efficacy relative to the unconjugated AMP analogues.

Catalytically Active Peptide-Gold Nanoparticle Conjugates: Prospecting for Artificial Enzymes.

The self-assembly of peptides onto the surface of gold nanoparticles has emerged as a promising strategy towards the creation of artificial enzymes. The resulting high local peptide density surrounding the nanoparticle leads to cooperative and synergistic effects, which result in rate accelerations and distinct catalytic properties compared to the unconjugated peptide. This Minireview summarizes contributions to and progress made in the field of catalytically active peptide-gold nanoparticle conjugates. The origin of distinct properties, as well as potential applications, are also discussed.

The Impact of Halogenated Phenylalanine Derivatives on NFGAIL Amyloid Formation.

The hexapeptide hIAPP22-27 (NFGAIL) is known as a crucial amyloid core sequence of the human islet amyloid polypeptide (hIAPP) whose aggregates can be used to better understand the wild-type hIAPP's toxicity to ß-cell death. In amyloid research, the role of hydrophobic and aromatic-aromatic interactions as potential driving forces during the aggregation process is controversially discussed not only in case of NFGAIL, but also for amyloidogenic peptides in general. We have used halogenation of the aromatic residue as a strategy to modulate hydrophobic and aromatic-aromatic interactions and prepared a library of NFGAIL variants containing fluorinated and iodinated phenylalanine analogues. We used thioflavin T staining, transmission electron microscopy (TEM) and small-angle X-ray scattering (SAXS) to study the impact of side-chain halogenation on NFGAIL amyloid formation kinetics. Our data revealed a synergy between aggregation behavior and hydrophobicity of the phenylalanine residue. This study introduces systematic fluorination as a toolbox to further investigate the nature of the amyloid self-assembly process.

Catalytic Activity of Peptide-Nanoparticle Conjugates Regulated by a Conformational Change.

Herein, we present the design and synthesis of a catalytically active peptide-nanoparticle conjugate whose activity is regulated by a defined conformational change in the self-assembled peptide monolayer. A catalytically active peptide, designed after the heterodimeric α-helical coiled-coil principle was immobilized onto gold nanoparticles, and kinetic studies were performed according to the Michaelis-Menten model. The formed peptide monolayer at the gold nanoparticle surface accelerated p-nitrophenylacetate (pNPA) hydrolysis by 1 order of magnitude compared to the soluble peptide while exhibiting no defined secondary structure as determined by infrared (IR) and circular dichroism (CD) spectroscopy. Addition of the complementary peptide-induced coiled-coil formation while significantly hindering the pNPA hydrolysis catalyzed by the peptide-nanoparticle conjugate. The heptad repeat sequence of a coiled-coil opens up the opportunity for regulation of conformation and thus catalytic activity of peptide-nanoparticle conjugates upon interaction with a complementary coiled-coil sequence. Strategies of regulation of catalytic activity by interaction with a complementary cofactor/ligand are well-established in nature and are introduced here into rationally designed peptide-nanoparticle conjugates.

Substrate specificity of an actively assembling amyloid catalyst.

In the presence of Zn2+ , the catalytic, amyloid-forming peptide Ac-IHIHIQI-NH2 , was found to exhibit enhanced selectivity for hydrophobic p-nitrophenyl ester substrates while in the process of self-assembly. As opposed to the substrate p-nitrophenyl acetate, which was more effectively hydrolyzed with Ac-IHIHIQI-NH2 in its fully fibrillar state, the hydrophobic substrate Z-L-Phe-ONp was converted with a second-order rate constant more than 11-times greater when the catalyst was actively assembling. Under such conditions, Z-L-Phe-ONp hydrolysis proceeded at a greater velocity than the more hydrophilic and otherwise more labile ester Boc-L-Asn-ONp. When assembling, the catalyst also showed increased selectivity for the L-enantiomer of Z-Phe-ONp. These findings suggest the occurrence of increased interactions of hydrophobic moieties of the substrate with exposed hydrophobic surfaces of the assembling peptides and present valuable features for future de novo design consideration.