Structural and functional relationship of Cassia obtusifolia trypsin inhibitor to understand its digestive resistance against Pieris rapae

Integrated transcriptomic and metabolomic analysis reveals the molecular basis of tissue-specific accumulation of bioactive steroidal alkaloids in Fritillaria unibracteata

Fritillaria unibracteata is an endangered medicinal plant whose bulb has been used as a Chinese herb to suppress cough, asthma and excessive phlegm for centuries. Steroidal alkaloids, which are synthesized via the steroid synthesis pathways, are their significant bioactive constituents. However, few studies on genes involved in steroidal alkaloid biosynthesis in F. unibracteata have been reported, mainly due to the lack of the F. unibracteata genome. In this paper, comparative transcriptomic and metabolomic analyses of four different tissues of F. unibracteata (leaves, flowers, stems, and bulbs) were performed. Imperialine, peiminine, and peimisine were among the significant bioactive compounds that were considerably abundant in bulb tissue, according to the metabolomic findings. Then, 83.60 Gb transcriptome sequencing of four different tissues was performed, of which one gene encoding phosphomevalonate kinase was directly functionally characterized to verify the accuracy of sequences obtained from the transcriptome. A total of 9217 differentially expressed unigenes (DEGs) were identified in four different tissues of F. unibracteata. GO and KEGG enrichments revealed that phenylpropanoid biosynthesis, MVA-mediated terpenoid backbone biosynthesis, and steroid biosynthesis were enriched in bulb tissue, whereas enrichment of MEP-mediated terpenoid backbone biosynthesis, photosynthesis, photosynthesis-antenna protein and carotenoid biosynthesis was observed in aerial tissues. Moreover, clustering analysis indicated that the downstream steroid biosynthesis pathway was more important in steroidal alkaloid biosynthesis compared to the upstream terpenoid backbone biosynthesis pathway. Hence, MVA-mediated biosynthesis of steroidal alkaloids was proposed, in which 15 bulb-clustered DEGs were positively correlated with a high accumulation of bioactive steroid alkaloids, further validating our proposal. In addition, 36 CYP450s showing a positive correlation with bioactive steroidal alkaloids provided candidate enzymes to catalyze the subsequent steps of steroidal alkaloid biosynthesis. In addition, the transcription factors and ABC transporters clustered in bulb tissue might be responsible for the regulation and transportation of steroidal alkaloid biosynthesis. Protein-protein interaction analysis implied a highly complex steroid alkaloid biosynthesis network in which delta (24)-sterol reductase might be one of the central catalysts. Based on the integrated transcriptome and metabolome, this current study is a first step in understanding the tissue-specific biosynthesis of steroidal alkaloids in F. unibracteata. Furthermore, key genes and regulators identified herein could facilitate metabolic engineering to improve steroidal alkaloids in F. unibracteata.

Preparation and activity evaluation of angiotensin-I converting enzyme inhibitory peptides from protein hydrolysate of mulberry leaf

Angiotensin-I converting enzyme (ACE) inhibitory peptides drew wide attention in the food industry because of their natural reliability, non-toxicity, and safety. However, the characteristics of ACE inhibitory peptides obtained from protein hydrolysate of mulberry leaf prepared by Flavourzyme were still unclear. Based on the single-factor test, the Plackett-Burman test and response surface test were used to determine the key factors affecting the ACE inhibition rate in mulberry leaf protein hydrolysate and the optimum conditions of enzymatic hydrolysis. The results showed that the optimum technical parameters were as follows: the ratio of material to liquid is 1: 25 (w / v, g/mL), the Flavourzyme to substrate ratio was 3,000 U/g, the temperature of enzymatic hydrolysis was 50°C, pH was 6.3, and the time of enzymatic hydrolysis was 2.9 h. The ACE inhibitory peptides in the mulberry leaf protein hydrolysates were purified by ultrafiltration and gel filtration, aiming to obtain the highest active component. The 12 peptide sequences were identified by reverse liquid chromatography-mass spectrometry, and then, they were docked to the crystal structure of human angiotensin-I converting enzyme (1O8A), and the interaction mechanisms of 12 peptide sequences and 1O8A were analyzed. The docking results showed that among the 12 peptide sequences, ERFNVE (792.37 Da), TELVLK (351.72 Da), MELVLK (366.72 Da), and FDDKLD (376.67 Da), all had the lowest docking energy, and inhibition constant. The chemosynthetic ERFNVE (IC₅₀: 2.65 mg/mL), TELVLK (IC₅₀: 0.98 mg/mL), MELVLK (IC₅₀:1.90 mg/mL) and FDDKLD (IC₅₀:0.70 mg/mL) demonstrated high ACE-inhibitory activity with competitive inhibition mode. These results indicated that the ACE-inhibiting peptides from mulberry leaf protein hydrolyzed (FHMP) had the potential activities to inhibit ACE and could be used as functional food or drugs to inhibit ACE. This work provides positive support for mining the biological activity of mulberry leaves in the treatment of hypertension.

A phenylalanine ammonia lyase from Fritillaria unibracteata promotes drought tolerance by regulating lignin biosynthesis and SA signaling pathway

Drought is one of the key threatening environmental factors for plant and agriculture. Phenylalanine ammonia lyase (PAL) is a key enzyme involved in plant defense against abiotic stress, however, the role of PAL in drought tolerance remains elusive. Here, a PAL member (FuPAL1) containing noncanonical Ala-Ser-Gly triad was isolated from Fritillaria unibracteata, one important alpine pharmaceutical plant. FuPAL1, mainly distributed in cytosol, was more conserved than FuCOMT and FuCHI at both nucleotide and amino acid levels. FuPAL1 was overexpressed in Escherichia coli and the purified recombinant FuPAL1 protein showed catalytic preference on L-Phe than L-Tyr. Homology modeling and site-mutation of FuPAL1 exhibited FuPAL1 took part in the ammonization process by forming MIO-like group, and Phe141, Ser208, Ileu218 and Glu490 played key roles in substrate binding and (or) catalysis. HPLC analysis showed that lignin and salicylic acid levels increased but total flavonoid levels decreased in FuPAL1 transgenic Arabidopsis compared to wild-type plants. Moreover, FuPAL1 transgenic Arabidopsis significantly enhanced its drought tolerance, which suggested that FuPAL1 mediated tolerance to drought by inducing the biosynthesis and accumulation of salicylic acid and lignin. Taken together, our results confirmed that the FuPAL1 played an important role in drought tolerance, and FuPAL1 might be a valuable target for genetic improvement of drought resistance in future.

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 basis of the caffeic acid O-methyltransferase from Ligusiticum chuanxiong to understand its selective mechanism

Caffeic acid O-methyltransferase from Ligusticum chuanxiong (LcCOMT) showed strict regiospecificity despite a relative degree of preference. Compared with caffeic acid, methyl caffeate was the preferential substrate by its low Km and high Kcat. In this study, we obtained the SAM binary (1.80 Å) and SAH binary (1.95 Å) complex LcCOMT crystal structures, and established the ternary complex structure with methyl caffeate by molecular docking. The active site of LcCOMT included phenolic substrate pocket, SAM/SAH ligand pocket and conserved catalytic residues as well. The regiospecificity of LcCOMT that permitted only 3-hydroxyl group to be methylated arise from the interactions between the active site and the phenyl ring. However, the propanoid tail governed the relative preference of LcCOMT. The ester group in methyl caffeate stabilized the anionic intermediate caused by His268-Asp269 pair, whereas caffeic acid was unable to stabilize the anionic intermediate due to the adjacent carboxylate anion in the propanoid tail. Ser183 residue formed an additional hydrogen bond with SAH and its role was identified by S183A mutation. Ile318 residue might be a potential site for determination of substrate preference, and its mutation led to the change of tertiary conformation. The results supported the selective mechanism of LcCOMT.

Biologia futura: medicinal plants-derived bioactive peptides in functional perspective-a review

Bioactive peptides (BPs) are 3-20 amino acid residues, with a molecular weight lower than 6 kDa; originated from the breakdown of proteins by endogenous and exogenous peptidases. While intact in protein these peptides do not exert any biological activity, but as they release from their parent protein, they exert various pharmacological activities such as antidiabetic, antihypertensive, anticancerous, anti-inflammatory, antimicrobial, antioxidant, and immunomodulatory. Such peptides exist in all living organism like plants, animals, marine organism and also present in food products derived from them. BPs obtained from dairy food products, cereals, vegetables have been gaining much more importance now-a-days, but little work has been done on bioactive peptides obtained from medicinal plants. Some of the medicinal plants such as Tinospora cordifolia Sterculia foetida, Benincasa hispida, Parkia speciosa, Linum usitatissimum, Salvia hispanica and Ziziphus jujube have been explored for bioactive peptides. Current review is aimed to provide a complete information of medicinal plants derived BPs along with the surge of new materials, new plants which will provide more solutions for handling some of the major human health problems of twenty-first century. This review will also be helpful to researchers in providing valuable information about the extraction, separation, characterization of BPs, their known peptide sequences and various pharmacological activities exerted by medicinal plants-derived bioactive peptides.

In vitro screening of peptidase inhibitory activity in some plants of North India

In the present study, trypsin and chymotrypsin inhibitory activity of some plants of different families was evaluated. A total of 55 plants were screened, out of which six showed the maximum trypsin inhibitory activity namely Acacia concinna, Caesalpinia bonducella, Lathyrus sativus, Mucuna pruriens, Psoralea corylifolia and Sapindus mukorossi. Results suggested that the plants showing trypsin inhibitory activity (TIA) also have chymotrypsin inhibitory activity (CIA). Both trypsin and chymotrypsin inhibitory activities were high in seeds compared to leaves followed by flowers. It was also observed that TIA was maximally present in Sapindaceae family whereas CIA was maximum in fabaceae family followed by others.

Functional Stability and Structural Transitions of a Kunitz trypsin Inhibitor from Chickpea (CaTI2)

Enzymes are important tools for various applications. We have studied structural transitions and functional stability of a Kunitz trypsin inhibitor from Chickpea (CaTI2), a potent insect gut-protease inhibitor, under different stress conditions like non-neutral pH, elevated temperature and co-solvent concentrations. CaTI2 was cloned and expressed in an eukaryotic system P. pastoris and was investigated for conformational transitions using circular dichroism spectroscopy, differential scanning fluorimetry and activity assay. Native CaTI2 has a sheet dominant structure with 40% β sheets and possess a single tryptophan residue situated in the hydrophobic core of the enzyme. The recombinant inhibitor maintained its maximum activity under alkaline pH with its secondary structure intact between pH 6-10. CaTI2 was observed to be thermally stable up to 55 °C with a T_m of 61.3 °C above which the protein unfolds. On treating with chemical denaturant (urea), the CaTI2 lost its inhibitory potential and native conformation beyond 2 M urea concentration. Moreover, the protein unfolded at lower temperatures as the concentration of denaturant increased, suggesting more complex structural changes. Further, the stability of the inhibitor was found to be directly proportional to the solvent polarity. The data, herein offers significant information of inhibitor stability and activity which could be exploited for its further development into an effective pesticide.