Rapid Formation of Intramolecular Disulfide Bridges using Light: An Efficient Method to Control the Conformation and Function of Bioactive Peptides.

Disulfide bonds are widely found in natural peptides and play a pivotal role in stabilizing their secondary structures, which are highly associated with their biological functions. Herein, we introduce a light-mediated strategy to effectively control the formation of disulfides. Our strategy is based on 2-nitroveratryl (oNv), a widely used photolabile motif, which serves both as a photocaging group and an oxidant (after photolysis). We demonstrated that irradiation of oNv-caged thiols with UV light could release free thiols that are rapidly oxidized by locally released byproduct nitrosoarene, leading to a "break-to-bond" fashion. This strategy is highlighted by the in situ restoration of the antimicrobial peptide tachyplesin I (TPI) from its external disulfide-caged analogue TPI-1. TPI-1 exhibits a distorted structure and a diminished function. However, upon irradiation, the ß-hairpin structure and membrane activity of TPI were largely restored via rapid intramolecular disulfide formation. Our study proposes a powerful method to regulate the conformation and function of peptides in a spatiotemporal manner, which has significant potential for the design of disulfide-centered light-responsive systems.

Customized Reversible Stapling for Selective Delivery of Bioactive Peptides.

We have developed a new concept for reversible peptide stapling that involves macrocyclization between two amino groups and decyclization promoted via dual 1,4-elimination. Depending on the trigger moiety, this strategy could be employed to selectively deliver peptides to either intracellular or extracellular targets. As a proof of concept, a peptide inhibitor targeting a lysine-specific demethylase 1 (LSD1) was temporarily cyclized to enhance its stability and ability to cross the cell membrane. Once inside the cells, the biologically active linear peptide was released under reducing environment. Moreover, we have developed reversibly stapled peptides using antimicrobial peptides (RStAMPs) whose bioactive helical conformation can be temporarily destabilized by stapling the peptide backbone. The resulting helix-distorted RStAMPs are nontoxic and highly resistant to protease hydrolysis, while at the infection site, RStAMPs can be rapidly activated by the overproduced H2O2 through the dual 1,4-elimination. The latter restored the helical structure of the native peptide and its antimicrobial activity. This work illustrates a highly valuable macrocyclization strategy for the peptide community and should greatly benefit the field of peptide delivery.

Polymyxin B-inspired non-hemolytic tyrocidine A analogues with significantly enhanced activity against gram-negative bacteria: How cationicity impacts cell specificity and antibacterial mechanism.

Naturally occurring cyclic antimicrobial peptides (AMPs) such as tyrocidine A (Tyrc A) and gramicidin S (GS) are appealing targets for the development of novel antibiotics. However, their therapeutic potentials are limited by undesired hemolytic activity and relatively poor activity against Gram-negative bacteria. Inspired by polycationic lipopeptide polymyxin B (PMB), the so called 'last-resort' antibiotic for the treatment of infections caused by multidrug-resistant Gram-negative bacteria, we synthesized and biologically evaluated a series of polycationic analogues derived from Tyrc A. We were able to obtain peptide 8 that possesses 5 positive charges exhibiting potent activities against both Gram-negative and Gram-positive bacteria along with totally diminished hemolytic activity. Intriguingly, antibacterial mechanism studies revealed that, rather than the 'pore forming' model that possessed by Tyrc A, peptide 8 likely diffuses membrane in a 'detergent-like' manner. Furthermore, when treating mice with peritonitis-sepsis, peptide 8 showed excellent antibacterial and anti-inflammatory activities in vivo.

In-Situ-Bloomed Micrometer-Scale Ultrathin Nanosheets in Tumor-Microenvironment for Intensive Photothermal-Enhanced Chemodynamic Therapy.

Chemodynamic therapy (CDT), as the emerging modality of cancer therapy based on Fenton or Fenton-like reactions, still suffers from low efficacy of hydroxyl radical generation, which requires full exposure of reaction sites of CDT nanoagents to intracellular H2O2. However, the amount of exposed reaction sites is severely restrained by the controlled size (<200 nm) and the limited specific surface area of nanoagents. Herein, we highlight the in-situ bloomed micrometer-scale CoMn-based layered double hydroxide (CoMn-LDH) ultrathin nanosheets, which are derived from CoMn boride-based CMB@ss-SF nanospheres in response to overexpressed glutathione (GSH) and dissolved oxygen in tumor microenvironment (TME), accomplishing intensive photothermal-enhanced CDT. The micrometer-scale CoMn-LDH ultrathin nanosheets would provide abundant reactive sites to accelerate heterogeneous Fenton-like reaction as well as GSH depletion, eliciting quick release of metal ions and further realizing intensive homogeneous Fenton-like reactions for ·OH generation. Moreover, the nanoagent can harvest 808 nm light into heat, which can be utilized to promote the CDT efficacy and realize photoacoustic imaging (PAI). Because of acidity and overexpressed GSH in TME, the nanoagent exhibited superior biodegradability. Benefiting from the synergistic advantages, CMB@ss-SF with negligible cytotoxicity completely eradicated the tumors in mouse. This work provides avenue for developing CDT nanoagents.