Isolation and characterization of a protease inhibitor from Acacia karroo with a common combining loop and overlapping binding sites for chymotrypsin and trypsin

Development of a rapid process for purification of Bowman-Birk and Kunitz inhibitors from legume seeds, and evaluation of their biophysical, insecticidal, and antimicrobial properties

Bowman-Birk inhibitor (BBI ~10 kDa) and Kunitz inhibitor (KI ~20 kDa) are serine protease/proteinase inhibitor(s) [PI(s)] ubiquitously found in several Leguminous plant species with insecticidal and therapeutic properties. Due to narrow molecular mass differences, the separation of these inhibitors from a single seed variety is tedious. The present study is aimed to develop a rapid protocol (<24 h) for purifying BBI and KI from legume seeds using mild trichloroacetic acid (TCA) extraction followed by trypsin-affinity chromatography. The mature seeds of Vigna radiata and Cajanus platycarpus are used as a model to purify BBI and KI using this protocol. The BBI and KI purified from the seeds of V. radiata are labeled as VrBBI & VrKI, and C. platycarpus are labeled as CpBBI & CpKI, respectively. These PIs are confirmed by immunodetection and MALDI-TOF studies and further characterized for their structural (CD & fluorescence spectroscopy) and functional properties (temperature & DTT stability). BBI(s) purified using the above process are effective in the management of castor semi-looper 'Achaea janata', while KI(s) are effective in the management of pod borer 'Helicoverpa armigera'. Besides, both BBI(s) and KI(s) have significant potential in controlling the growth of methicillin-sensitive 'Staphylococcus aureus', a gram-positive pathogenic bacterium.

Plant Kunitz Inhibitors and Their Interaction with Proteases: Current and Potential Pharmacological Targets

The action of proteases can be controlled by several mechanisms, including regulation through gene expression; post-translational modifications, such as glycosylation; zymogen activation; targeting specific compartments, such as lysosomes and mitochondria; and blocking proteolysis using endogenous inhibitors. Protease inhibitors are important molecules to be explored for the control of proteolytic processes in organisms because of their ability to act on several proteases. In this context, plants synthesize numerous proteins that contribute to protection against attacks by microorganisms (fungi and bacteria) and/or invertebrates (insects and nematodes) through the inhibition of proteases in these organisms. These proteins are widely distributed in the plant kingdom, and are present in higher concentrations in legume seeds (compared to other organs and other botanical families), motivating studies on their inhibitory effects in various organisms, including humans. In most cases, the biological roles of these proteins have been assigned based mostly on their in vitro action, as is the case with enzyme inhibitors. This review highlights the structural evolution, function, and wide variety of effects of plant Kunitz protease inhibitors, and their potential for pharmaceutical application based on their interactions with different proteases.

TcTI, a Kunitz-type trypsin inhibitor from cocoa associated with defense against pathogens

Protease inhibitors (PIs) are important biotechnological tools of interest in agriculture. Usually they are the first proteins to be activated in plant-induced resistance against pathogens. Therefore, the aim of this study was to characterize a Theobroma cacao trypsin inhibitor called TcTI. The ORF has 740 bp encoding a protein with 219 amino acids, molecular weight of approximately 23 kDa. rTcTI was expressed in the soluble fraction of Escherichia coli strain Rosetta [DE3]. The purified His-Tag rTcTI showed inhibitory activity against commercial porcine trypsin. The kinetic model demonstrated that rTcTI is a competitive inhibitor, with a Ki value of 4.08 × 10-7 mol L-1. The thermostability analysis of rTcTI showed that 100% inhibitory activity was retained up to 60 °C and that at 70-80 °C, inhibitory activity remained above 50%. Circular dichroism analysis indicated that the protein is rich in loop structures and β-conformations. Furthermore, in vivo assays against Helicoverpa armigera larvae were also performed with rTcTI in 0.1 mg mL-1 spray solutions on leaf surfaces, which reduced larval growth by 70% compared to the control treatment. Trials with cocoa plants infected with Mp showed a greater accumulation of TcTI in resistant varieties of T. cacao, so this regulation may be associated with different isoforms of TcTI. This inhibitor has biochemical characteristics suitable for biotechnological applications as well as in resistance studies of T. cacao and other crops.

Exploration of anti-insect potential of trypsin inhibitor purified from seeds of Sapindus mukorossi against Bactrocera cucurbitae

Peptidase inhibitors (PIs) are defense proteins of plants which are active against gut peptidases of different insects. Sapindus mukorossi was identified as a source of bioactive PIs which could confer resistance against Bactrocera cucurbitae, a most devastating pest of several economically important crops. In the present study, a trypsin inhibitor was purified from mature dry seeds of S. mukorossi and characterized for its biochemical properties as well as its potential for bio control of B. cucurbitae. The purified fractions from RP- HPLC through SDS-PAGE gave an apparent molecular weight of ~29 kDa. S. mukorossi trypsin inhibitor (SMTI) was found to be a non-competitive inhibitor which was active over a broad range of temperature (10–100 °C) and pH (6–11). SMTI when incorporated in artificial diet inhibited the growth and development of B. cucurbitae larvae. Gene expression analysis of trypsin and chymotrypsin genes via qRT-PCR indicated that their mRNA expression was down-regulated while that of other genes namely, Catalase, Elastase, Superoxide Dismutase, Glutathione –S-transferase and Alkaline Phosphatase was up regulated. SMTI also showed deleterious effects against different bacterial strains. The results of this study indicated that S. mukorossi trypsin inhibitor has potential to be used as a bio control agent that can reduce the harm caused by melon fruit fly and other devastating pests.

Primary Structure of a Trypsin Inhibitor (Copaifera langsdorffii Trypsin Inhibitor-1) Obtained from C. langsdorffii Seeds

In this study, the aim was to determine the complete sequence of the Copaifera langsdorffii trypsin inhibitor (CTI)-1 using 2-dimensional (2D)-PAGE, matrix-assisted laser desorption ionization-time-of-flight (MALDI-TOF), and quadrupole time-of-flight (QTOF) spectrometry. Spots A (CTI-1) and F (CTI-2) were submitted to enzymatic digestions with trypsin, SV8, and clostripain. The accurate mass of the peptide obtained from each digest was determined by mass spectrometry (MS) using MALDI-TOF. The most abundant peptides were purified and sequenced in a liquid chromatograph connected to an electrospray ionization-QTOF MS. When the purified trypsin inhibitor was submitted to 2D electrophoresis, different spots were observed, suggesting that the protein is composed of 2 subunits with microheterogeneity. Isoelectric points of 8.0, 8.5, and 9.0 were determined for the 11 kDa subunit and of 4.7, 4.6, and 4.3 for the 9 kDa subunit. The primary structure of CTI-1, determined from the mass of the peptide of the enzymatic digestions and the sequence obtained by MS, indicated 180 shared amino acid residues and a high degree of similarity with other Kunitz (KTI)-type inhibitors. The peptide also contained an Arg residue at the reactive site position. Its 3-dimensional structure revealed that this is because the structural discrepancies do not affect the canonical conformation of the reactive loop of the peptide. Results demonstrate that a detailed investigation of the structural particularities of CTI-1 could provide a better understanding of the mechanism of action of these proteins, as well as clarify its biologic function in the seeds. CTI-1 belongs to the KTI family and is composed of 2 polypeptide chains and only 1 disulfide bridge.