Modular peptides from the thermoplastic squid sucker ring teeth form amyloid-like cross-ß supramolecular networks.

The hard sucker ring teeth (SRT) from decapodiforme cephalopods, which are located inside the sucker cups lining the arms and tentacles of these species, have recently emerged as a unique model structure for biomimetic structural biopolymers. SRT are entirely composed of modular, block co-polymer-like proteins that self-assemble into a large supramolecular network. In order to unveil the molecular principles behind SRT's self-assembly and robustness, we describe a combinatorial screening assay that maps the molecular-scale interactions between the most abundant modular peptide blocks of suckerin proteins. By selecting prominent interaction hotspots from this assay, we identified four peptides that exhibited the strongest homo-peptidic interactions, and conducted further in-depth biophysical characterizations complemented by molecular dynamic (MD) simulations to investigate the nature of these interactions. Circular Dichroism (CD) revealed conformations that transitioned from semi-extended poly-proline II (PII) towards ß-sheet structure. The peptides spontaneously self-assembled into microfibers enriched with cross ß-structures, as evidenced by Fourier-Transform Infrared Spectroscopy (FTIR) and Congo red staining. Nuclear Magnetic Resonance (NMR) experiments identified the residues involved in the hydrogen-bonded network and demonstrated that these self-assembled ß-sheet-based fibers exhibit high protection factors that bear resemblance to amyloids. The high stability of the ß-sheet network and an amyloid-like model of fibril assembly were supported by MD simulations. The work sheds light on how Nature has evolved modular sequence design for the self-assembly of mechanically robust functional materials, and expands our biomolecular toolkit to prepare load-bearing biomaterials from protein-based block co-polymers and self-assembled peptides. STATEMENT OF SIGNIFICANCE: The sucker ring teeth (SRT) located on the arms and tentacles of cephalopods represent as a very promising protein-based biopolymer with the potential to rival silk in biomedical and engineering applications. SRT are made of modular, block co-polymer like proteins (suckerins), which assemble into a semicrystalline polymer reinforced by nano-confined ß-sheets, resulting in a supramolecular network with mechanical properties that match those of the strongest engineering polymers. In this study, we aimed to understand the molecular mechanisms behind SRT's self-assembly and robustness. The most abundant modular peptidic blocks of suckerin proteins were studied by various spectroscopic methods, which demonstrate that SRT peptides form amyloid-like cross-ß structures.

Catechol-functionalized chitosan/iron oxide nanoparticle composite inspired by mussel thread coating and squid beak interfacial chemistry.

Biological materials offer a wide range of multifunctional and structural properties that are currently not achieved in synthetic materials. Herein we report on the synthesis and preparation of bioinspired organic/inorganic composites that mimic the key physicochemical features associated with the mechanical strengthening of both squid beaks and mussel thread coatings using chitosan as an initial template. While chitosan is a well-known biocompatible material, it suffers from key drawbacks that have limited its usage in a wider range of structural biomedical applications. First, its load-bearing capability in hydrated conditions remains poor, and second it completely dissolves at pH < 6, preventing its use in mild acidic microenvironments. In order to overcome these intrinsic limitations, a chitosan-based organic/inorganic biocomposite is prepared that mimics the interfacial chemistry of squid beaks and mussel thread coating. Chitosan was functionalized with catechol moieties in a highly controlled fashion and combined with superparamagnetic iron oxide (γ-Fe2O3) nanoparticles to give composites that represent a significant improvement in functionality of chitosan-based biomaterials. The inorganic/organic (γ-Fe2O3/catechol) interfaces are stabilized and strengthened by coordination bonding, resulting in hybrid composites with improved stability at high temperatures, physiological pH conditions, and acid/base conditions. The inclusion of superparamagnetic particles also makes the composites stimuli-responsive.

Synthesis and extended activity of triazole-containing macrocyclic protease inhibitors.

Peptide-derived protease inhibitors are an important class of compounds with the potential to treat a wide range of diseases. Herein, we describe the synthesis of a series of triazole-containing macrocyclic protease inhibitors pre-organized into a ß-strand conformation and an evaluation of their activity against a panel of proteases. Acyclic azido-alkyne-based aldehydes are also evaluated for comparison. The macrocyclic peptidomimetics showed considerable activity towards calpain II, cathepsin L and S, and the 20S proteasome chymotrypsin-like activity. Some of the first examples of highly potent macrocyclic inhibitors of cathepsin S were identified. These adopt a well-defined ß-strand geometry as shown by NMR spectroscopy, X-ray analysis, and molecular docking studies.

New tripeptide-based macrocyclic calpain inhibitors formed by N-alkylation of histidine.

Two new series of 15-membered macrocyclic peptidomimetics, in which the P1 and P3 residues of the peptide backbone are linked by a bridge containing a 1,4-disubstituted 1H-imidazole, are reported. The structure with an aldehyde at the C-terminus and the imidazole at P3, i.e., 4c, shows significant inhibitory activity against calpain 2, with an IC(50) value of 238 nM. The macrocyclic aldehyde with the imidazole at the alternative P1 position, i.e., 5c, is significantly less active. The relative activities are linked to the ability of the component macrocycles to mimic a ß-strand geometry that is known to favor active-site binding. This ability is defined by conformational searches and docking studies with calpain.

5-benzylidenerhodanine and 5-benzylidene-2-4-thiazolidinedione based antibacterials.

Herein we outline the antibacterial activity of amino acid containing thiazolidinediones and rhodanines against Gram-positive bacteria Staphylococcus aureus ATCC 31890, Staphylococcus epidermidis and Bacillus subtilis ATCC 6633. The rhodanine derivatives were generally more active than the analogous thiazolidinediones. Compounds of series 5 showed some selectivity for Bacillus subtilis ATCC 6633, the extent of which is enhanced by the inclusion of a non-polar amino acid at the 5-position of the core thiazolidinediones and rhodanines scaffolds. SAR data of series 8 demonstrated improved activity against the clinically more significant Staphylococci with selectivity over Bacillus subtilis ATCC 6633 induced by introduction of a bulky aryl substituent at the 5-position of the core scaffolds.

Electron transfer through α-peptides attached to vertically aligned carbon nanotube arrays: a mechanistic transition.

The mechanism of electron transfer in α-aminoisobutyric (Aib) homoligomers is defined by the extent of secondary structure, rather than just chain length. Helical structures (Aib units ≥3) undergo an electron hopping mechanism, while shorter disordered sequences (Aib units <3) undergo an electron superexchange mechanism.

Biotin analogues with antibacterial activity are potent inhibitors of biotin protein ligase.

There is a desperate need to develop new antibiotic agents to combat the rise of drug-resistant bacteria, such as clinically important Staphylococcus aureus. The essential multifunctional enzyme, biotin protein ligase (BPL), is one potential drug target for new antibiotics. We report the synthesis and characterization of a series of biotin analogues with activity against BPLs from S. aureus, Escherichia coli, and Homo sapiens. Two potent inhibitors with K i < 100 nM were identified with antibacterial activity against a panel of clinical isolates of S. aureus (MIC 2-16 µg/mL). Compounds with high ligand efficiency and >20-fold selectivity between the isozymes were identified and characterized. The antibacterial mode of action was shown to be via inhibition of BPL. The bimolecular interactions between the BPL and the inhibitors were defined by surface plasmon resonance studies and X-ray crystallography. These findings pave the way for second-generation inhibitors and antibiotics with greater potency and selectivity.

Carbenoid insertion into the peroxide bond vs the olefin bond of cyclic peroxides.

Herein we report examples of the insertion of a carbenoid into a peroxide linkage. This study reveals that intramolecular insertion of carbenes into the peroxide linkage of 3,6-dihydro-1,2-dioxines is preferred over olefin insertion. The initial scope of the reaction and mechanistic considerations, have been probed. This methodology also generates unusual bicyclic hemiacetals (2) and tricyclic peroxides (3).