Protein and Peptide Letters - Volume 30, Issue 4, 2023

Protein and peptide drugs have been considered to be valuable for treating disease for many years, capturing more and more of the attention of researchers. Previously, we found a short peptide from the porcine intestine named COX52-69, which could simultaneously lower blood glucose and insulin response after intraperitoneal injection. And thus, it showed a potential to counter type II diabetes without leading to insulin resistance, mainly caused by high insulin levels in the blood. However, this molecule is not stable in the digestive system and cannot be used via oral administration. Here we employed the circularization technique to modify the peptide and tested its pharmacokinetics.

The high global burden of tuberculosis (TB) and the increasing emergence of the drugresistant (DR) strain of Mycobacterium tuberculosis (Mtb) emphasize the urgent need for novel antimycobacterial agents. Antimicrobial peptides (AMPs) are small peptides widely existing in a variety of organisms and usually have amphiphilic cationic structures, which have a selective affinity to the negatively charged bacterial cell wall. Besides direct bactericidal mechanisms, including interacting with the bacterial cell membrane and interfering with the biosynthesis of the cell wall, DNA, or protein, some AMPs are involved in the host's innate immunity. AMPs are promising alternative or complementary agents for the treatment of DR-TB, given their various antibacterial mechanisms and low cytotoxicity. A large number of AMPs, synthetic or natural, from human to bacteriophage sources, have displayed potent anti-mycobacterial activity in vitro and in vivo. In this review, we summarized the features, antimycobacterial activity, and mechanisms of action of the AMPs according to their sources. Although AMPs have not yet met the expectations for clinical application due to their low bioavailabilities, high cost, and difficulties in large-scale production, their potent antimycobacterial activity and action mechanisms, which are different from conventional antibiotics, make them promising antibacterial agents against DR-Mtb in the future.

Background: Unlike other subtypes of breast cancer, triple negative breast cancer (TNBC) exhibits aggressive and metastatic behaviors and a lack of effective targeted therapeutics. (R)-9bMS, a small-molecule inhibitor of the non-receptor tyrosine kinase 2 (TNK2), significantly inhibited TNBC cell growth; however, the functional mechanism of (R)-9bMS in TNBC remains largely unknown. Objective: To explore the functional mechanism of (R)-9bMS in TNBC. Methods: Cell proliferation, apoptosis and xenograft tumor growth assays were performed to evaluate the effects of (R)-9bMS on TNBC. The expression levels of miRNA and protein were detected by RTqPCR or western blot, respectively. Protein synthesis was determined by analyzing the polysome profile and ³⁵S-met incorporation. Results: (R)-9bMS attenuated TNBC cell proliferation, induced cell apoptosis, and inhibited xenograft tumor growth. Mechanism study indicated that (R)-9bMS upregulated the expression of miR-4660 in TNBC cells. The expression of miR-4660 is lower in TNBC samples than that of the non-cancerous tissues. miR-4660 overexpression inhibited TNBC cell proliferation by targeting the mammalian target of rapamycin (mTOR), which reduced mTOR abundance in TNBC cells. Consistent with the downregulation of mTOR, exposure of (R)-9bMS inhibited the phosphorylation of p70S6K and 4E-BP1, which consequently interrupted the total protein synthesis and autophagy of TNBC cells. Conclusion: These findings uncovered the novel working mechanism of (R)-9bMS in TNBC by attenuating mTOR signaling via up-regulating miR-4660. The potential clinical significance of (R)- 9bMS in TNBC treatment is interesting to explore.

Background: Pancreatic cancer metastasis is characterized by a higher incidence of morbidity and mortality. The present study attempts to identify phytocomponents with the potential to inhibit the secretion of MMP-2 by pancreatic cancer cells and ascertain the efficacy of individual components. Methods: Overall survival analysis carried out revealed reduced survival of patients with high MMP-2 expression. Data analysis from TCGA revealed increased MMP-2 expression in pancreatic cancer patients compared to adjacent normal tissues. The expression of MMP-2 was reported at different stages of pancreatic cancer (Stage I-IV). To understand the relevance of phytocomponents in binding to the catalytic site of MMP-2, molecular docking studies were performed to find the effectiveness based on Glide score/energy. To substantiate the in-silico analysis, the eight components were also tested in vitro for reducing the survival in PANC-1 cells at three different time points (24, 48, and 72 hours). Finally, zymography analysis was performed using the eight components in the PANC-1 conditioned media of treated cells to ascertain the enzymatic activity of MMP-2. Results: The obtained results suggest plumbagin, emodin, and EGCG exert potential inhibition in PANC-1 cells, among other phytocomponents tested. Therefore, as assessed using computational studies, the binding ability of plumbagin, emodin, and EGCG can be interpreted as inhibiting effects on MMP-2 activities. Conclusion: These compounds could find potential application in preventing the progression, sustenance, and metastasis of pancreatic cancer and need to be explored further using a pre-clinical model system in order to validate the efficacy, bioavailability, and safety.

Background: Gastric cancer (GC) is the most common cancer globally. Recent research has suggested that circular RNAs (circRNAs) play crucial roles in GC tumorigenesis and progression. The present study is performed to clarify the possible mechanism of circRNA has_circ_0006089 (circ_0006089) in GC. Methods: The differentially expressed circRNAs were screened out by analyzing the dataset GSE83- 521. Quantitative real-time polymerase chain reaction (qRT-PCR) was performed to detect circ_0006089, miR-515-5p and CXCL6 expression levels in GC tissues and cell lines. CCK-8, BrdU and Transwell assays were adopted to examine the biological function of circ_0006089 in GC cells. The interaction between miR-515-5p and circ_0006089, as well as between CXCL6 and miR-515-5p, was confirmed through bioinformatics, RNA immunoprecipitation (RIP) assay, dual-luciferase reporter gene assay and RNA pull-down assay. Results: Circ_0006089 was significantly upregulated in GC tissues and cells, and miR-515-5p was remarkably downregulated. After knocking down circ_0006089 or overexpressing miR-515-5p, the growth, migration and invasion of GC cells were markedly reduced. In terms of mechanism, miR-515- 5p was verified to be the target of circ_0006089, and CXCL6 was validated as miR-515-5p’s downstream target gene. Inhibiting miR-515-5p reversed the inhibitory effect knocking down circ_0006089 had on GC cell proliferation, migration and invasion. Conclusion: Circ_0006089 facilitates the malignant biological behaviors of GC cells via the miR-515- 5p/CXCL6 axis. Circ_0006089 can probably act as one of the important biomarkers and therapeutic targets in GC treatment strategies.

Introduction: A complex study of the antioxidant system enzymes (AOS) is an important subject of biochemical research; changes in the activity of these enzymes can be used as a biochemical marker of various processes in plants. At the same time, practically little attention has been paid to describing the regularities of these enzymatic reactions in different wood formation processes, such as xylogenesis. This article discusses the outcomes of different behaviors of AOS enzymes, which are involved in both the redistribution of the ROS balance and phenolic compounds at the early stages of wood formation in young plants of silver birch (Betula pendula Roth) with straight-grained wood and Karelian birch (Betula pendula Roth var. carelica (Merckl.) Hamet-Ahti) with non-figured and figured parts within the single trunk. Background: Spectrophotometric determination of AOS enzymes’ activity can be used as a biochemical marker in the different wood formation processes, including xylogenesis. In this study, we studied structural anomalies of the woody plant trunk of Karelian birch (Betula pendula Roth var. carelica (Merckl.) Hamet- Ahti). Objective: This study aimed to study AOS enzymes’ activity in 12-year-old plants of silver birch (Betula pendula Roth) with straight-grained wood and Karelian birch (Betula pendula Roth var. carelica (Merckl.) Hamet-Ahti) with non-figured and figured parts within the single trunk. Methods: Plant tissues were ground in liquid nitrogen to a uniform mass and homogenized at 4°C in the buffer containing 50 mM HEPES (pH 7.5), 1 mM EDTA, 1 mM EGTA, 3 mM DTT, 5 mM MgCl2, and 0.5 mM PMSF. After 20 min extraction, the homogenate was centrifuged at 10000 g for 20 min (MPW-351R, Poland). The sediment was washed in the buffer thrice. The pooled supernatant and sediment were dialyzed at 4°C for 18-20 h against a tenfold diluted homogenization buffer. The enzymes' activity was determined spectrophotometrically (Spectrophotometer SF-2000, OKB Spectr, Russia). Proteins in the extracts were quantified by the method of Bradford. Results: We observed different behaviors of the studied enzymes involved in both the redistribution of the ROS balance and phenolic compounds with subsequent lignification even at the early stages of wood formation in young plants and even in different trunk parts within a tree, which was consistent with results obtained earlier on adult plants. High SOD activity in the phloem compared to the activity in the xylem was accompanied by higher CAT activity. The POD/SOD ratio was significantly higher in the figured trunk parts in Karelian birch compared to other variants in the xylem and higher in Karelian birch plants compared to plants of common birch in the phloem. The CAT/POD ratio was significantly higher in plants with no signs of anomalies. The high POD and PPO activity in the xylem of figured trunk parts and in the phloem of figured and non-figured trunk parts of B. pendula var. carelica can be associated with the high activity of apoplast invertase. Conclusion: The study showed that at the stage of active formation of structural anomalies in the figured trunk parts in young plants of Karelian birch, hydrogen peroxide utilization occurred mainly due to increased POD activity. An increase in PPO activity in the trunk of figured plants could also be considered an indicator of the formation of structural anomalies. At the same time, in areas with developing abnormal wood, the POD/SOD ratio increased, and the CAT/POD ratio decreased, indicating a fine-tuning of the balance between superoxide radical and hydrogen peroxide, which, when changed, might regulate the rearrangement of xylogenesis towards proliferation in relation to differentiation.

Background: Hevea brasiliensis is severely affected by the fungal disease caused by Phytophthora spp. Significant loss of rubber yield is widespread and extensive use of chemical fungicides has resulted in health and environmental problems. Objective: This work aims to extract and identify the latex serum peptides from a disease tolerant clone of H. brasiliensis, and study the inhibitory efficacy against pathogenic bacteria and fungi. Methods: Serum peptides were extracted from H. brasiliensis BPM24 using mixed lysis solution. Low molecular weight peptides were screened and fractionated by solid-phase extraction and then identified by tandem mass spectrometry. Total and fractionated serum peptides were assayed for bacterial and fungal inhibition using broth microdilution and poisoned food methods. An inhibitory control study in the greenhouse was also performed using susceptible clones for pre and postinfection with Phytophthora spp. Results: Forty-three serum peptide sequences were successfully identified. Thirty-four peptides matched with the proteins associated with plant defense response signaling, host resistance, and adverse environmental factors. The inhibitory study of total serum peptides demonstrated antibacterial and anti-fungal properties. The greenhouse study exhibited disease inhibitory efficacy of 60% for the treatment of Phytophthora spp. in post-infected plants and 80% for pre-treated samples. Conclusion: Latex serum peptides from disease tolerant H. brasiliensis revealed several proteins and peptides associated with plant defense and disease resistance. The peptides play a vital role for defense against bacteria and fungi pathogens, including Phytophthora spp. Enhanced disease protection can be obtained when the extracted peptides were applied to the susceptible plants before exposure to the fungi. These findings provided an insight and may pave the way for the development of biocontrol peptides from natural resources.

Introduction: Catechol o-methyltransferase plays a key role in the metabolism of catecholamine neurotransmitters. At present, its catalytic mechanism, overall structure, and kinetic characteristics have been basically clarified, but few people have paid attention to the function of solvents on enzymatic methyl transfer reactions. The influence of solvents on enzymatic reactions has always been a fuzzy hot topic. In addition, as a well-studied typical methyltransferase, COMT is a good test bed for exploring the source of the solvent isotope effect, which is a powerful tool in enzymatic mechanism research. Methods: We have measured the kinetic parameters of methyl transfer catalyzed by COMT in both normal water (H2O) and heavy water (D2O) by high-performance liquid chromatography (HPLC) in the range of pL 6 ~ 11. Results: The kinetic characteristics of COMT in H2O and D2O were significantly different under different pH/pD conditions. Significant solvent kinetic isotope effects (SKIE) were obtained, especially inverse solvent kinetic isotope effects (SKIE < 1) were observed in this methyl transfer reaction for the first time. Conclusion: Traditional factors which could interpret the solvent isotope effect were ruled out. It’s suggested that the solvent might affect the overall conformation as well as the flexibility of protein through non-covalent forces, thus altering the catalytic activity of COMT and leading to the solvent isotope effect.