Double Orthogonal Click Reactions for the Development of Antimicrobial Peptide Nanotubes

Co-assembled Coiled-Coil Peptide Nanotubes with Enhanced Stability and Metal-Dependent Cargo Loading

Peptide nanotube biomaterials are attractive for their range of applications. Herein, we disclose the co-assembly of coiled-coil peptides, one with ligands for metal ions that demonstrate hierarchical assembly into nanotubes, with spatial control of the metal-binding ligands. Enhanced stability of the nanotubes to phosphate-buffered saline was successfully accomplished in a metal-dependent fashion, depending on the levels and placement of the ligand-containing coiled-coil peptide. This spatial control also allowed for site-specific labeling of the nanotubes with His-tagged fluorophores through the length of the tubes or at the termini, in a metal-dependent manner.

Partition of antimicrobial D-L-α-cyclic peptides into bacterial model membranes

Fluorescence spectroscopy is used to characterize the partition of three second-generation D,L-α-cyclic peptides to two lipid model membranes. The peptides have proven antimicrobial activity, particularly against Gram positive bacteria, and the model membranes are formed of either with 1,2-dimyristoyl-sn-glycero-3-phospho-(1'-rac-glycerol) (DMPG) or its mixture with 1,2-dimyristoyl-sn-glycero-3-phosphoethanolamine (DMPE), at a molar ratio of (1:1). The peptide's intrinsic fluorescence was used in the Steady State and/or Time Resolved Fluorescence Spectroscopy experiments, showing that the peptides bind to the membranes, and the extent of their partition is thereof quantified. The peptide-induced membrane leakage was followed using an encapsulated fluorescent dye. Overall, the partition is mainly driven by electrostatics, but also involves hydrophobic interactions. The introduction of a hydrocarbon tail in one of the residues of the parent peptide, CPR, adjacent to the tryptophan (Trp) residue, significantly improves the partition of the modified peptides, CPRT10 and CPRT14, to both membrane systems. Further, we show that the length of the tail is the main distinguishing factor for the extension of the partition process. The parent peptide induces very limited leakage, at odds with the peptides with tail, that promote fast leakage, increasing in most cases with peptide concentration, and being almost complete for the highest peptide concentration and negatively charged membranes. Overall, the results help the unravelling of the antimicrobial action of these peptides and are well in line with their proven high antimicrobial activity.

Glycan shields for penetrating peptides

We here describe the synthesis and biological evaluation of glycan shields for cell penetrating peptides. A new benzyl alkoxyamine connector was employed for the coupling of two saccharides units in the lateral side chain of individual amino acids in a peptide sequence. The oxyme bond formation with the corresponding glycan aldehydes allowed the preparation of highly glycosylated penetrating peptides with a minimal synthetic effort. Surprisingly, it was found that a four to six saccharide substitution did not decrease uptake efficiency in cells, whereas it significantly improved the toxicity profile of the penetrating peptide. In particular, glucose substitution was confirmed as an optimal glycan shield that showed an excellent in vitro uptake and intracellular localization as well as a superior in vivo biodistribution.

1D alignment of proteins and other nanoparticles by using reversible covalent bonds on cyclic peptide nanotubes

Peptide nanotubes deposit on mica surface can be used for the alignment of proteins thank to the use of dynamic covalent bonds that allow the incorporation of appropriate ligands on nanotube surface.

Macromolecular assembly and membrane activity of antimicrobial D,L-α-Cyclic peptides

Antimicrobial peptides are viewed as a promising alternative to conventional antibiotics, as their activity through membrane targeting makes them less prone to resistance development. Among them, antimicrobial D,L-α-cyclic peptides (CPs) have been proposed as an alternative, specially due to their cyclic nature and to the presence of D-α-amino acids that increases their resistance to proteases. In present work, second generation D,L-α-cyclic peptides with proven antimicrobial activity are shown to form complex macromolecular assemblies in the presence of membranes. We addressed the CPs:membrane interactions through a combination of experimental techniques (DSC and ATR-FTIR) with coarse-grained molecular dynamics (CG-MD) simulations, aiming at understanding their interactions, macromolecular assemblies and eventually unveil their mechanism of action. DSC shows that the interaction depends heavily on the negatively charge content of the membrane and on lipid/peptide ratio, suggesting different mechanisms for the different peptides and lipid systems. CG-MD proved that CPs can self-assemble at the lipid surface as nanotubes or micellar aggregates, depending on the peptide, in agreement with ATR-FTIR results. Finally, our results shed light into possible mechanisms of action of the peptides with pending hydrocarbon tail, namely membrane extensive segregation and/or membrane disintegration through the formation of disk-like lipid/peptide aggregates.

Attenuated total reflection-Fourier transform infrared spectroscopy: a tool to characterize antimicrobial cyclic peptide-membrane interactions

Attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) has been used for the structural characterization of peptides and their interactions with membranes. Antimicrobial peptides (AMPs) are part of our immune system and widely studied in recent years. Many linear AMPs have been studied, but their cyclization was shown to enhance the peptide's activity. We have used cyclic peptides (CPs) of an even number of alternating D- and L-α-amino acids, an emerging class of potential AMPs. These CPs can adopt a flat-ring shape that can stack into an antiparallel structure, forming intermolecular hydrogen bonds between different units, creating a tubular β-sheet structure - self-assembled cyclic peptide nanotubes (SCPNs). To get the structural information on peptides in solution and/or in contact with membranes, Amide I and II absorptions are used as they can adopt frequency and shape band characteristics that are influenced by the strength of existing hydrogen bonds between the amide CO and NH involved in secondary structures such as helix, β-sheet or aperiodic structures. The combination of polarized lens with ATR-FTIR provides an important tool to study the orientation of peptides when interacting with lipid membranes as the information can be derived on the position relative to the membrane normal. This work shows how ATR-FTIR used together with polarized light was successfully used to characterize structurally two CPs (RSKSWPgKQ and RSKSWX^C10KQ) in solution and upon interaction with negatively charged membranes of DMPG, assessing the formation and orientation of tubular structures (SCPNs) that were shown to be enhanced by the presence of the lipid membrane.