Antifungal activity of α-helical propeptide SnuCalCpI15 derived from Calotropis procera R. Br. against food spoilage yeasts

Heterologous expression of a papain-like protease inhibitor (SnuCalCpI17) in the E. coli and its mode of inhibition

The effect of the Escherichia coli (E. coli) Rosetta (DE3) system on the expression of recombinant papain-like cysteine protease inhibitors (SnuCalCpIs) was evaluated, and the inhibition mode of the expressed inhibitor was determined. SnuCalCpI08 and SnuCalCpI17, which previously had not been expressed in the E. coli BL21 (DE3) system due to rare codons of more than 10%, were successfully expressed in E. coli Rosetta (DE3) since the strain provides tRNAs for six rare codons. Initially, both inhibitors were expressed as inclusion bodies; however, the water solubility of SnuCalCpI17 could be improved by lowering the incubation temperature, reducing the IPTG concentration, and increasing the induction time. In contrast, the other inhibitor could not be solubilized in water. To validate whether the inhibitor was expressed with correct protein folding, a papain inhibition assay was performed with SnuCalCpI17. SnuCalCpI17 showed a half-maximal inhibitory concentration (IC₅₀) of 105.671 ± 9.857 µg/mL and a slow-binding inhibition mode against papain at pH 7.0 with a K_i^app of 75.80 μg/mL. The slow-binding inhibitor has a slow dissociation from the inhibitor-target complex, resulting in a long residence time in vivo, and thus can effectively inhibit the target at doses far below the IC₅₀ of the inhibitor. KEY POINTS: • Propeptide inhibitor (SnuCalCpI17) containing rare codons was expressed in E. coli Rosetta (DE3). • The slow-binding inhibition was shown by plotting the apparent first-order rate constant (k_obs). • Protein-protein interaction between SnuCalCpIs and papain was verified by docking simulation.

Antimicrobial, Antigenotoxicity, and Characterization of Calotropis procera and Its Rhizosphere-Inhabiting Actinobacteria: In Vitro and In Vivo Studies

Calotropis procera (C. procera) is a wild shrub that is a medicinal plant found in abundance throughout Saudi Arabia. In this study, we investigated the phytochemical composition and antigenotoxic properties of the ethanolic extract of C. procera, in addition to the antimicrobial activity of the plant and its rhizospheric actinobacteria effects against pathogenic microorganisms. Soil-extract medium supplemented with glycerol as a carbon source and starch–casein agar medium was used for isolation of actinobacteria from rhizosphere. From the plant, a total of 31 compounds were identified using gas chromatography/mass spectrometry (GC–MS). The main components were α-amyrin (39.36%), lupeol acetate (17.94%), phytol (13.32%), hexadecanoic acid (5.55%), stigmasterol (3.16%), linolenic acid (3.04%), and gombasterol A (2.14%). C. procera plant extract’s antimicrobial activity was investigated using an agar well-diffusion assay and minimum inhibitory concentration (MIC) against six pathogenic microbial strains. The plant extract of C. procera was considered significantly active against Staphylococcus aureus, Klebsiella pneumonia, and Escherichia coli, with inhibition zones of 18.66 mm, 21.26 mm, and 21.93 mm, respectively. The plant extract was considered to be a moderate inhibitor against Bacillus subtilis, with MIC ranging from 0.60–1.50 mg/mL. On the other hand, the isolated actinobacteria were considered to be a moderate inhibitor against S. aureus (MIC of 86 µg/mL), and a potent inhibitor, strain CALT_2, against Candida albicans (MIC of 35 µg/mL). The 16S rRNA gene sequence analysis showed that the potential strains belonged to the genus Streptomyces. The effect of C. procera extract against cyclophosphamide (CP)-induced genotoxicity was examined by evaluating chromosome abnormalities in mouse somatic cells and DNA fragmentation assays. The current study revealed that oral pretreatment of C. procera (50, 100, and 200 mg/kg b.w.) for 1, 7, and 14 days to cyclophosphamide-treated animals significantly reduced chromosomal abnormalities as well as DNA fragmentation in a dose-dependent manner. Moreover, C. procera extract had antimicrobial and antigenotoxic effects against CP-induced genotoxicity.

Designing Self-Assembling Chimeric Peptide Nanoparticles with High Stability for Combating Piglet Bacterial Infections

As a novel type of antibiotic alternative, peptide-based antibacterial drug shows potential application prospects attributable to their unique mechanism for lysing the membrane of pathogenic bacteria. However, peptide-based antibacterial drugs suffer from a series of problems, most notably their immature stability, which seriously hinders their application. In this study, self-assembling chimeric peptide nanoparticles (which offer excellent stability in the presence of proteases and salts) are constructed and applied to the treatment of bacterial infections. In vitro studies are used to demonstrate that peptide nanoparticles NPs1 and NPs2 offer broad-spectrum antibacterial activity and desirable biocompatibility, and they retain their antibacterial ability in physiological salt environments. Peptide nanoparticles NPs1 and NPs2 can resist degradation under high concentrations of proteases. In vivo studies illustrate that the toxicity caused by peptide nanoparticles NPs1 and NPs2 is negligible, and these nanoparticles can alleviate systemic bacterial infections in mice and piglets. The membrane permeation mechanism and interference with the cell cycle differ from that of antibiotics and mean that the nanoparticles are at a lower risk of inducing drug resistance. Collectively, these advances may accelerate the development of peptide-based antibacterial nanomaterials and can be applied to the construction of supramolecular nanomaterials.