Preparation and Irreversible Inhibition Mechanism Insight into a Recombinant Kunitz Trypsin Inhibitor from Glycine max L. Seeds

A Novel Trypsin Kunitz-Type Inhibitor from Cajanus cajan Leaves and Its Inhibitory Activity on New Cancer Serine Proteases and Its Effect on Tumor Cell Growth

A novel trypsin inhibitor from Cajanus cajan (TIC) fresh leaves was partially purified by affinity chromatography. SDS-PAGE revealed one band with about 15 kDa with expressive trypsin inhibitor activity by zymography. TIC showed high affinity for trypsin (Ki = 1.617 μM) and was a competitive inhibitor for this serine protease. TIC activity was maintained after 24 h of treatment at 70 °C, after 1 h treatments with different pH values, and β-mercaptoethanol increasing concentrations, and demonstrated expressive structural stability. However, the activity of TIC was affected in the presence of oxidizing agents. In order to study the effect of TIC on secreted serine proteases, as well as on the cell culture growth curve, SK-MEL-28 metastatic human melanoma cell line and CaCo-2 colon adenocarcinoma was grown in supplemented DMEM, and the extracellular fractions were submitted salting out and affinity chromatography to obtain new secreted serine proteases. TIC inhibited almost completely, 96 to 89%, the activity of these serine proteases and reduced the melanoma and colon adenocarcinoma cells growth of 48 and 77% respectively. Besides, it is the first time that a trypsin inhibitor was isolated and characterized from C. cajan leaves and cancer serine proteases were isolated and partial characterized from SK-MEL-28 and CaCo-2 cancer cell lines. Furthermore, TIC shown to be potent inhibitor of tumor protease affecting cell growth, and can be one potential drug candidate to be employed in chemotherapy of melanoma and colon adenocarcinoma.

Continuous monitoring of chemical signals in plants under stress

Time is an often-neglected variable in biological research. Plants respond to biotic and abiotic stressors with a range of chemical signals, but as plants are non-equilibrium systems, single-point measurements often cannot provide sufficient temporal resolution to capture these time-dependent signals. In this article, we critically review the advances in continuous monitoring of chemical signals in living plants under stress. We discuss methods for sustained measurement of the most important chemical species, including ions, organic molecules, inorganic molecules and radicals. We examine analytical and modelling approaches currently used to identify and predict stress in plants. We also explore how the methods discussed can be used for applications beyond a research laboratory, in agricultural settings. Finally, we present the current challenges and future perspectives for the continuous monitoring of chemical signals in plants.

Urease and α-Chymotrypsin Inhibitory Activities and Molecular Docking Studies of Alkaloids Isolated from Medicinal Plant Isatis minima Bunge

Phytochemical studies on the alkaloids fraction of the entire plant of Isatis minima Bunge resulted in the alkaloids 1–4 isolation, which were first time isolated from this species. The 1D and 2D NMR spectroscopic data were used to identify their structures, and there was satisfactory compatibility of the data compared to those which were previously published. In the examined compounds 1–4, Isaindigotidione (3) and Isaindigotone (4) were shown as an effective urease inhibitor in such a concentration-dependent way against Jack bean and Bacillus pasteurii urease, with IC₅₀ values 29.03 ± 0.04, 20.04 ± 0.09 and 34.03 ± 0.07, 26.13 ± 0.08 μM, respectively. Compounds 3 and 4 were likewise shown to be an effective inhibitor against α-chymotrypsin, exhibiting IC₅₀ values 16.09 ± 0.07 and 22.01 ± 0.06 μM, correspondingly. The program MOE-Dock was used to perform a molecular docking analysis to confirm probable binding modes of the active complexes of the isolated compounds 1–4 and the crystal structure of urease and α-chymotrypsin enzymes. Compound 3 was the most active, having the highest docking scores against Bacillus pasteurii urease, α-chymotrypsin, and Jack bean (−8.6876), (−7.6647), and (−13.1927) μM, respectively. All four alkaloids (1–4) showed significant urease and protease inhibitory potential and further these activities were confirmed with the help of molecular docking study.

Heterologous expression and physicochemical characteristics identification of Kunitz protease inhibitor in Brassica napus

A Kunitz protease inhibitor gene (RTI; rti) was cloned from rapeseed and expressed in a Pichia pastoris expression system for the first time. After isolation and purification, the physical and chemical characteristics of the inhibitor were analyzed. The results showed that the induced expression level of the recombinant RTI reached 628 mg/L, and the specific activity of the inhibitor reached 69.6 TIU/mg protein at the shake flask fermentation level; the recombinant RTI retained more than 70% inhibitory activity between 30 and 90 °C and more than 80% inhibitory activity between pH 2.0-11.0. The metal ions Cu²⁺ and CO²⁺ and the organic reagents methanol, ethanol, acetone, and chloroform inhibit its activity. The recombinant RTI interacts with trypsin in a noncompetitive manner and has a strong and specific inhibitory effect on trypsin, a typical Kunitz trypsin inhibitor from plants. Combined with its good physical and chemical properties, recombinant RTI has the potential to be developed into an insect resistance protein.

Structure-Activity Relationship and Molecular Docking of a Kunitz-Like Trypsin Inhibitor, Kunitzin-AH, from the Skin Secretion of Amolops hainanensis

Kunitz-like trypsin inhibitors are one of the most noteworthy research objects owing to their significance in pharmacological studies, including anticarcinogenic activity, obesity regulation and anticoagulation. In the current study, a novel Kunitz-like trypsin inhibitor, Kunitzin-AH, was isolated from the skin secretion of Amolops hainanensis. The novel peptide displayed a modest trypsin inhibitory activity with the inhibitor constant (K_i) value of 1.18 ± 0.08 µM without inducing damage to healthy horse erythrocytes. Then, a series of shortened variants of Kunitzin-AH were designed by truncating a peptide loop and site mutation inside the loop to illustrate the structure–activity relationship of the trypsin inhibition function. Among the variants, a significant decrease was observed for the Cys-Cys loop domain, while the extension of an Arg at N-terminus (RCKAAFC) retained the inhibitory activity, indicating that the -RCK-motif is essential in forming the reactive domain for exerting the inhibitory activity. Furthermore, substitutions of Ala by hydrophobic or hydrophilic residues decreased the activity, indicating suitable steric hindrance provides convenience for the combination of trypsin. Additionally, the conformational simulation of the analogues processed with Chimera and Gromacs and further combination simulations between the peptides and trypsin conducted with HDOCK offered a potential opportunity for the natural trypsin inhibitory drug design. The truncated sequence, AH-798, may be a good replacement for the full-length peptide, and can be optimized via cyclization for further study.