Bangzhi Zhang

Two Hits Are Better than One: Membrane Active and DNA Binding Related Double Action Mechanism of NK-18, a Novel Antimicrobial Peptide Derived from Mammalian NK-lysin

ABSTRACT The extensive use and misuse of antibiotics in medicine result in the emergence of multidrug-resistant bacteria, creating an urgent need for the development of new chemotherapeutic agents. Nowadays, antimicrobial peptides are widely recognized as a class of promising candidates with activity against multidrug-resistant bacteria. NK-18 is a truncated peptide derived from NK-Lysin, an effector of cytotoxic T cells and natural killer cells. In this study, we studied the antibacterial mechanism of action of NK-18. The results revealed that NK-18 has potent antibacterial activity against Escherichia coli and Staphylococcus aureus. According to our findings, NK-18 is membrane active and its target of action is not only the bacterial membrane but also the DNA in the cytoplasm. The double targets of NK-18 make it difficult for bacteria to generate resistance, which may present a new strategy to defend against multidrug-resistant bacteria and provide a new lead in the design of potent antimicrobial peptides with therapeutic application in the presence of increasing resistance to conventional antibiotics.

Catalytic Asymmetric [3 + 2] Cyclization Reactions of 3-Isothiocyanato Oxindoles and Alkynyl Ketones Via an in Situ Generated Magnesium Catalyst

A highly enantioselective formal [3 + 2] cycloaddition reaction between 3-isothiocyanato oxindoles and alkynyl ketones is reported for the first time. An oxazoline-OH type chiral ligand derived from o-hydroxy-phenylacetic acid is employed to generate an effective magnesium catalyst in the current cyclization reaction and give serials of chiral spirooxindoles with good chemical yields and enantioselectivities.

Membrane active antitumor activity of NK-18, a mammalian NK-lysin-derived cationic antimicrobial peptide

As the increasing emergence of multi-drug resistant tumor cells, there is an urgent need for developing new chemotherapeutic agents. NK-lysin was a novel effector of cytotoxic T cells and natural killer (NK) cells and had broad antimicrobial activity. In this study, we developed a core region of NK-lysin termed NK-18, and studied its antitumor activity and possible action mode. Our results showed that NK-18 (with 18 amino acids) possesses potent antitumor activity against bladder and prostate cancer cells by disrupting the integrity of cell membrane, but has negligible hemolysis activity against mouse erythrocytes. In addition, CD spectra was employed to study its conformation in membrane mimicking environment. NK-18 takes a standard α-helical conformation in membrane mimicking environment, which could be accounted for its more potent antitumor activity compared with its low α-helical content homologous derivatives. These findings together with its shorter amino acid sequence and lower synthesis cost suggest that NK-18 could present an alternative therapeutic strategy to cancer chemotherapy and play a promising role in fighting the multi-drug resistant tumors.

Dual antifungal properties of cationic antimicrobial peptides polybia-MPI: Membrane integrity disruption and inhibition of biofilm formation

With the increasing emergence of resistant fungi, the discovery and development of novel antifungal therapeutics were urgently needed. Compared with conventional antibiotics, the limited propensity of AMPs to induce resistance in pathogens has attracted great interest. In the present study, the antifungal activity and its mechanism-of-action of polybia-MPI, a cationic peptide from the venom of Social wasp Polybia Paulista was investigated. We demonstrated that polybia-MPI could potently inhibit the growth of Candida albicans (C. albicans) and Candida glabrata (C. glabrata). The 50% inhibitory concentrations (IC50) of Polybia-MPI against cancer cells were much higher than the MICs against the tested C. albicans and C. glabrata cells, indicating that polybia-MPI had high selectivity between the fungal and mammalian cells. Our results also indicated that membrane disturbance mechanism was involved in the antifungal activity. Furthermore, polybia-MPI could inhibit the bio film forming of C. glabrata, which was frequently associated with clinically significant biofilm. These results suggest that polybia-MPI has great advantages in the development of antifungal agents.

Membrane active antimicrobial activity and molecular dynamics study of a novel cationic antimicrobial peptide polybia-MPI, from the venom of Polybia paulista

As the frequent emergence of the resistant bacteria, the development of new agents with a new action mode attracts a great deal of interest. It is now widely accepted that antimicrobial peptides (AMPs) are promising alternatives to conventional antibiotics. In this study, antimicrobial peptide polybia-MPI and its analogs were synthesized and their antibacterial activity was studied. Our results revealed that polybia-MPI has potent antibacterial activity against both Gram-positive and Gram-negative bacteria. Its ability to make PI permeate into bacteria and lead to the leakage of calcein from model membrane LUVs, suggests a killing mechanism involving membrane perturbation. SEM and TEM microscopy experiments verified that the morphology of bacteria was changed greatly under the treatment of polybia-MPI. Compared with the conventional chemotherapy, polybia-MPI targets the cell membrane rather than entering into the cell to exert its antibacterial activity. Furthermore, molecular dynamics (MD) simulations were employed to investigate the mechanism of membrane perturbation. The results indicated that the α-helical conformation in the membrane is required for the exhibition of antibacterial activity and the membrane disturbance by polybia-MPI is a cooperative process. In conclusion, with the increasing resistance to conventional antibiotics, there is no doubt that polybia-MPI could offer a new strategy to defend the resistant bacteria.

Membrane-active action mode of Polybia-CP, a novel antimicrobial peptide isolated from the venom of Polybia Paulista

ABSTRACT The extensive use of antibiotics in medicine, the food industry, and agriculture has resulted in the frequent emergence of multidrug-resistant bacteria, which creates an urgent need for new antibiotics. It is now widely recognized that antimicrobial peptides (AMPs) could play a promising role in fighting multidrug-resistant bacteria. Antimicrobial peptide polybia-CP was purified from the venom of the social wasp Polybia paulista. In this study, we synthesized polybia-CP and studied its action mode of antibacterial activity. Our results revealed that polybia-CP has potent antibacterial activity against both Gram-positive and Gram-negative bacteria. The results from both the real bacterial membrane and the in vitro model membrane showed that polybia-CP is membrane active and that its action target is the membrane of bacteria. It is difficult for bacteria to develop resistance to polybia-CP, which may thus offer a new strategy for defending against resistant bacteria in medicine and the food and farming industries.

Cellular uptake of transportan 10 and its analogs in live cells: Selectivity and structure-activity relationship studies.

Transportan 10 (TP10) is an amphipathic cell-penetrating peptide with high translocation ability. In order to obtain more details of structure-activity relationship of TP10, we evaluated the effects of structure and charge on its translocation ability. Our results demonstrated that disrupting the helical structure or Arg substitution could remarkably decrease the cellular uptake of TP10. However, increasing the number of positive charge was an effective strategy to enhance translocation ability of TP10. Furthermore, the molecular dynamics simulation supported the results derived from experiments, suggesting that higher membrane disturbance leads to higher cellular uptake of peptides. In addition, our study also demonstrated TP10 and its analogs preferentially entered cancer cells rather than normal cells. The uptake selectivity toward cancer cells makes TP10 and its analogs as potent CPPs for drug delivery.

Membrane Perturbation Action Mode and Structure-Activity Relationships of Protonectin, a Novel Antimicrobial Peptide from the Venom of the Neotropical Social Wasp Agelaia pallipes pallipes

ABSTRACT With the extensive use of antibiotics, multidrug-resistant bacteria emerge frequently. New antimicrobial agents with novel modes of action are urgently needed. It is now widely accepted that antimicrobial peptides (AMPs) could be promising alternatives to conventional antibiotics. In this study, we aimed to study the antimicrobial activity and mechanism of action of protonectin, a cationic peptide from the venom of the neotropical social wasp Agelaia pallipes pallipes. We demonstrated that protonectin exhibits potent antimicrobial activity against a spectrum of bacteria, including multidrug-resistant strains. To further understand this mechanism, the structural features of protonectin and its analogs were studied by circular dichroism (CD). The CD spectra demonstrated that protonectin and its natural analog polybia-CP formed a typical α-helical conformation in the membrane-mimicking environment, while its proline-substituted analog had much lower or even no α-helix conformation. Molecular dynamics simulations indicated that the α-helical conformation in the membrane is required for the exhibition of antibacterial activity. In conclusion, protonectin exhibits potent antimicrobial activity by disruption of the integrity of the bacterial membrane, and its α-helical confirmation in the membrane is essential for this action.

Antimicrobial activities and membrane-active mechanism of CPF-C1 against multidrug-resistant bacteria, a novel antimicrobial peptide derived from skin secretions of the tetraploid frog Xenopus clivii.

Hospital‐acquired infections caused by multidrug‐resistant bacteria pose significant challenges for treatment, which necessitate the development of new antibiotics. Antimicrobial peptides are considered potential alternatives to conventional antibiotics. The skin of Anurans (frogs and toads) amphibians is an extraordinarily rich source of antimicrobial peptides. CPF‐C1 is a typical cationic antimicrobial peptide that was originally isolated from the tetraploid frog Xenopus clivii. Our results showed that CPF‐C1 has potent antimicrobial activity against both sensitive and multidrug‐resistant bacteria. It disrupted the outer and inner membranes of bacterial cells. CPF‐C1 induced both propidium iodide uptake into the bacterial cell and the leakage of calcein from large liposome vesicles, which suggests a mode of action that involves membrane disturbance. Scanning electron microscopy and transmission electron microscopy verified the morphologic changes of CPF‐C1‐treated bacterial cells and large liposome vesicles. The membrane‐dependent mode of action signifies that the CPF‐C1 peptide functions freely and without regard to conventional resistant mechanisms. Additionally, it is difficult for bacteria to develop resistance against CPF‐C1 under this action mode. Other studies indicated that CPF‐C1 had low cytotoxicity against mammalian cell. In conclusion, considering the increase in multidrug‐resistant bacterial infections, CPF‐C1 may offer a new strategy that can be considered a potential therapeutic agent for the treatment of diseases caused by multidrug‐resistant bacteria. Copyright

Design of novel analogues of short antimicrobial peptide anoplin with improved antimicrobial activity

Currently, novel antibiotics are urgently required to combat the emergence of drug‐resistant bacteria. Antimicrobial peptides with membrane‐lytic mechanism of action have attracted considerable interest. Anoplin, a natural α‐helical amphiphilic antimicrobial peptide, is an ideal research template because of its short sequence. In this study, we designed and synthesized a group of analogues of anoplin. Among these analogues, anoplin‐4 composed of d‐amino acids displayed the highest antimicrobial activity due to increased charge, hydrophobicity and amphiphilicity. Gratifyingly, anoplin‐4 showed low toxicity to host cells, indicating high bacterial selectivity. Furthermore, the mortality rate of mice infected with Escherichia coli was significantly reduced by anoplin‐4 treatment relative to anoplin. In conclusion, anoplin‐4 is a novel anoplin analogue with high antimicrobial activity and enzymatic stability, which may represent a potent agent for the treatment of infection. Copyright