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Peptide-based helical barrels are a noteworthy building block for hierarchical assembly, with a hydrophobic cavity that can serve as a host for cargo. In this study, disulfide-stapled helical barrels were synthesized containing ligands for metal ions on the hydrophilic face of each amphiphilic peptide helix. The major product of the disulfide-stapling reaction was found to be composed of five amphiphilic peptides, thereby going from a 16-amino-acid peptide to a stapled 80-residue protein in one step. The structure of this pentamer, 5HB1, was optimized in silico, indicating a significant hydrophobic cavity of ~6 Å within a helical barrel. Metal-ion-promoted assembly of the helical barrel building blocks generated higher order assemblies with a three-dimensional (3D) matrix morphology. The matrix was decorated with hydrophobic dyes and His-tagged proteins both before and after assembly, taking advantage of the hydrophobic pocket within the helical barrels and coordination sites within the metal ion-peptide framework. As such, this peptide-based biomaterial has potential for a number of biotechnology applications, including supplying small molecule and protein growth factors during cell and tissue growth within the matrix.

 

Magnetic resonance imaging (MRI) is a medical imaging technique that provides detailed information on tissues and organs. However, the low sensitivity of the technique requires the use of contrast agents, usually ones that are based on the chelates of gadolinium ions. In an effort to improve MRI signal intensity, we developed two strategies whereby the ligand DOTA and Gd(III) ions are contained within Zn(II)-promoted collagen peptide (NCoH) supramolecular assemblies. The DOTA moiety was included in the assembly either via a collagen peptide sidechain (NHdota) or through metal–ligand interactions with a His-tagged DOTA conjugate (DOTA-His6). SEM verified that the morphology of the NCoH assembly was maintained in the presence of the DOTA-containing peptides (microflorettes), and EDX and ICP-MS confirmed that Gd(III) ions were incorporated within the microflorettes. The Gd(III)-loaded DOTA florettes demonstrated higher intensities for the T1-weighted MRI signal and higher longitudinal relaxivity (r1) values, as compared to the clinically used contrast agent Magnevist. Additionally, no appreciable cellular toxicity was observed with the collagen microflorettes loaded with Gd(III). Overall, two peptide-based materials were generated that have potential as MRI contrast agents. 

Coiled-coil peptides are exceptional building blocks for higher order assembly into materials with a rich variety of morphologies. These biomaterials have demonstrated an excellent range of biologically relevant applications as described herein. 

Here, the hierarchical assembly of a collagen mimetic peptide (CMP) displaying four bipyridine moieties is described. The CMP was capable of forming triple helices followed by self-assembly into disks and domes. Treatment of these disks and domes with metal ions such as Fe(II), Cu(II), Zn(II), Co(II), and Ru(III) triggered the formation of microcages, and micron-sized cup-like structures. Mechanistic studies suggest that the formation of the microcages proceeds from the disks and domes in a metal-dependent fashion. Fluorescently-labeled dextrans were encapsulated within the cages and displayed a time-dependent release using thermal conditions. 

The failure to treat everyday bacterial infections is a current threat as pathogens are finding new ways to thwart antibiotics through mechanisms of resistance and intracellular refuge, thus rendering current antibiotic strategies ineffective. Cell‐penetrating peptides (CPPs) are providing a means to improve antibiotics that are already approved for use. Through coadministration and conjugation of antibiotics with CPPs, improved accumulation and selectivity with alternative and/or additional modes of action against infections have been observed. Herein, we review the recent progress of this antibiotic–cell‐penetrating peptide strategy in combatting sensitive and drug‐resistant pathogens. We take a closer look into the specific antibiotics that have been enhanced, and in some cases repurposed as broad‐spectrum drugs. Through the addition and conjugation of cell‐penetrating peptides to antibiotics, increased permeation across mammalian and/or bacterial membranes and a broader range in bacterial selectivity have been achieved.

 

Mimicking the extracellular matrix (ECM) continues to be a goal in the field of regenerative medicine. Herein, we report a modified trimeric GCN4 coiled‐coil sequence containing three ligands for metal ions specifically positioned for crosslinked assembly (TriCross). In the presence of metal ions,TriCrossassembles into a three‐dimensional (3D) matrix with significant cavities to accommodate cells. The matrix was found to be stable in media with serum, and mild removal of the metal leads to disassembly. By assemblingTriCrosswith a suspension of cells in media, the matrix encapsulates cells during the assembly process leading to high cell viability. Further disassembly under mild conditions allows for the release of cells from the scaffold. As such, this peptide‐based material displays many of the characteristics necessary for successful 3D cell culture.

 

Metal ion‐mediated assembly of peptides is an intriguing method for developing novel biomaterials. In particular, peptide building blocks based on collagen triple helical and coiled‐coil peptides have been functionalized with metal‐binding ligands and assemble into hierarchical structures with diverse potential applications. This review outlines the use of metal‐mediated assembly with these supramolecular structures and highlights how changes in the building blocks lead to significant differences in structural morphologies, with the identity of the metal‐binding ligands and their placement on the building block as crucial aspects in the bottom‐up development of the assemblies.