Protein and Peptide Letters - Volume 30, Issue 3, 2023

Background: The DNA polymerase of Thermus thermophilus (Tth pol) presents reverse transcriptase activity with Mn²⁺, and can be used for one-step RT-qPCR. However, Mn²⁺ would reduce amplification fidelity and cause nonspecific products. Objective: Eliminating the Mn²⁺ dependence of the reverse transcriptase activity of Tth pol by point mutations. Methods: We constructed three variants I640F, I709K, and I640F/I709K, and measured their DNA polymerase and reverse transcriptase activities without Mn²⁺. Their enzymatic characteristics and PCR inhibitor resistance were also tested. Finally, these variants were applied in one-step RT-qPCR. Results: All three variants presented reverse transcriptase activity with Mg²⁺ only and increased DNA polymerase activity. The variants, except I709K, showed no significant difference in thermostability, optimal pH, optimal NaCl concentration, storage stability and PCR inhibitor resistance compared to the wild type. Variant I640F/I709K had good performance in one-step RT-qPCR with Mg²⁺ only, whereas both variants with single substitution exhibited nonspecific amplification. Conclusion: We successfully constructed three Tth pol variants possessing Mn²⁺ independent reverse transcriptase activity. The variant I640F/I709K was suitable for one-step RT-qPCR because of its good performance.

Chemotherapy is one of the most important treatment modalities for liver cancer, especially for those who are judged as being unsuitable for surgical resection, local ablative therapy, or transarterial chemoembolization. However, the efficacy of chemotherapy is still unsatisfactory due to the long duration, side effects and the tendency to develop drug resistance. The development of novel anti-liver cancer drugs remains imperative. Cyclopeptides have been recognized as new chemical modalities in drug design due to their unique constrained structures, extensive biological activities, higher metabolic stability, cell permeability and bioavailability than linear peptides. A lot of cyclic peptides have been found with potential anti-proliferative activity against malignant cells, and many of them showed excellent anti-liver cancer activity. In this review, we will discuss in detail the structures and the anti-liver cancer activity of small and medium-sized cyclopeptides, aiming to offer some elicitation to chemotherapeutic drug design based on cyclopeptides.

Background: Colon cancer has the second highest incidence rate of digestive system tumors. It relies on surgical treatment, radiotherapy and chemotherapy, and targeted drug therapy. Objective: To study the mechanism of GSN in the proliferation of colon cancer cells. Materials and Methods: The expression of gelsolin (GSN) was analyzed with the data of colon cancer patients in the TCGA database. SW620 cells were treated by GSN in vitro and the gene expression was detected by immunoblotting and quantitative PCR. Results: The expression of GSN was found significantly low in colon cancer cells and correlated with the prognosis of patients. The SW620 cell line cultured in vitro was treated with exogenous GSN. SW620 can be significantly inhibited above the concentration of 250 μg/ml. The results of immunoblotting and quantitative PCR showed that exogenous GSN can effectively improve the transcription level of death receptor-related pathway genes such as TNFR2 and CASP10. Conclusion: This study found that GSN inhibited the proliferation of SW620 cells in vitro by upregulating the expression of death receptor pathway-related proteins.

Background: Several reports have indicated that ultrasonication can change the solubility of muscle proteins and improves the functional properties of meat and isolated muscle proteins. Moreover, available literature suggests that ultrasonication can significantly improve the gelling properties of muscle proteins. Objectives: The present study was carried out to investigate the effect of low-frequency ultrasonication on the secondary structure of myosin and the impact of these structural changes on solubility and gelling ability. Methods: Myosin from breast muscles (Pectoralis major) of broiler chicken was extracted and exposed to low-frequency ultrasonication for 30 min. Four aliquots collected at the interval of 5, 10, 20, and 30 min were analysed for change in ATPase activity, sulfhydryl content, surface hydrophobicity, alpha-helicity. The possible impact of these changes on heat-induced gelation was observed through electron micrographs. Results: Ultrasonication reduced the enzymatic activity of myosin and increased the reactive sulfhydryl content. Decreased α-helicity and increased intrinsic fluorescence displayed significant structural changes at the secondary and tertiary levels. Myosin aggregation, as indicated by electron micrographs, showed a marked decrease. The microstructure of myosin gels displayed a distinct correlation with ultrasonication-induced structural changes. Furthermore, improved microstructure led to a significant increase in the water retention capacity of myosin gels. Conclusion: In conclusion, ultrasonication of myosin caused a marked change in structure at the tertiary and secondary levels. Structural changes apparently confined within the globular head region and rod portion of myosin were displayed by reduced enzymatic activity and improved gelation/solubility. Results of our study convincingly showed that ultrasonication improved the microstructure of myosin gels resulting in increased WHC.

Background: The CRISPR-Cas system is an adaptive immune mechanism for bacteria and archaea to resist foreign invasion. Currently, Cas9 and Cpf1 have been widely studied and applied in gene editing. C2c1 is a newly discovered CRISPR-Cas system endonuclease. It has broad application prospects due to its small molecular weight and high substrate recognition specificity. Objectives: Bacillus thermoamylovorans C2c1(BthC2c1) was expressed in E. coli C43 (DE3) competent cells, purified, and the BthC2c1-sgRNA-dsDNA complex was assembled. The effect of temperature on the cleavage ability of the BthC2c1 system was investigated. Methods: The cDNA of BthC2c1 was cloned into the vector pGEX-6P-1. BthC2c1 was expressed in E. coli C43(DE3) cells and purified using a GST affinity column and FPLC. The sgRNAs were transcribed and purified in vitro, and the complexes were assembled by gel filtration chromatography. The enzyme cleavage activity of BthC2c1 at different temperatures was investigated using an in vitro cleavage assay. Microscale Thermophoresis detected the affinity of the BthC2c1-sgRNA complexes to substrate DNA. Results: BthC2c1 proteins were prokaryotically expressed and purified. The complex of BthC2c1 with sgRNA and dsDNA was assembled. In vitro cleavage assay results showed that BthC2c1 cleaved the target DNA at temperatures ranging from 37°C to 67°C. The cleavage ability of BthC2c1 at 42^oC was stronger than that at 37^oC. The results of affinity detection showed that the affinity between the BthC2c1-sgRNA complex and ds36/36 at 42^oC was stronger than that at 37^oC. Conclusion: In this study, BthC2c1 was expressed, purified, and assembled into a complex with sgRNA and dsDNA. BthC2c1 cleaved DNA within the temperature range of 37^oC to 67^oC. The affinity of BthC2c1-sgRNA to DNA at 42°C was significantly enhanced than that at 37°C. It may be related to its stringent substrate recognition pattern, which differs from Cas9 and Cpf1. The temperature-dependent affinity changes of substrate binding may be part of the reason for the stronger cleavage activity of BthC2c1 at 42^oC. This study may provide an experimental basis for optimizing and modifying the C2c1 gene editing system.

Aims: Further investigation on the mechanism of action of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in NSCLC would shed light on the understanding of TRAIL resistance and provide new clues for the counter-strategy. Background: Cellular FLICE-inhibitory protein (c-FLIP) is a critical inhibitor of TRAIL-induced apoptosis. Our previous study suggested that glycogen synthase kinase 3β (GSK3β) positively regulated c-FLIP expression in human lung adenocarcinoma cells. Meanwhile, other studies reported that c-FLIP was degraded by HECT-type E3 ligase ITCH (Itchy E3 Ubiquitin Protein Ligase) via the proteasome pathway. Objective: We will explore whether ITCH is involved in the expression regulation of c-FLIP positively controlled by GSK3β during the treatment of TRAIL. Methods: Human lung adenocarcinoma cells were used to stably overexpress and knockdown GSK3β. Quantitative real-time PCR (qRT-PCR) assay was used to test the expressional level of mRNA of genes. Western blot analysis was employed to detect the expression of proteins at the protein level. siRNA of ITCH was used to knock down its expression. TRAIL treatment was used to cause apoptosis. Results: In the present study, we have confirmed the degradation of c-FLIP by ITCH protein and the downregulation of ITCH expression by GSK3β in lung adenocarcinoma cells. Moreover, ITCH silencing reversed the downregulation of c-FLIP protein caused by GSK3β-knockdown in the cells. Accordingly, TRAIL-induced apoptosis facilitated by GSK3β knockdown was blocked by the combined interference of ITCH. Conclusion: These results suggested that GSK3β/ITCH axis regulated the stability of c-FLIP and influenced TRAIL-induced apoptosis. Taken together, our study revealed a GSK3β/ITCH/c-FLIP axis, which counteracts TRAIL-induced apoptosis in human lung adenocarcinoma cells.

Background: Aloperine (ALO) is an important active component of quinolizidine alkaloids in Sophora flavescens A and Sophora alopecuroides L, and has effective anticancer activity against multiple cancers. However, the influence and mechanism of ALO on migration, invasion, and adhesion in bladder cancer cells remain unclear. Objective: The aim of this study is to determine the anticancer effect of ALO on migration, invasion, and adhesion in bladder cancer cells and to investigate its potential TIMP-4-related mechanism. Methods: Cell viability, cytotoxicity, wound healing, Transwell invasion, cell adhesion, real-time qPCR, western blot, and ELISA assays were performed to analyze the effect of ALO on migration, invasion, and adhesion in bladder cancer 5637 and UM-UC-3 cells. Furthermore, the anti-TIMP-4 antibody was used to explore the potential effect on ALO-inhibited bladder cancer cells. Results: We have found that ALO significantly suppressed migration, invasion, and adhesion in bladder cancer cells. Furthermore, ALO could downregulate the expression of MMP-2 and MMP-9 mRNAs and proteins, and increase the expression of TIMP-4 mRNA and protein. Moreover, the anti- TIMP-4 antibody reversed the prevention of migration, invasion, and adhesion in ALO-treated bladder cancer cells. Conclusion: The data in this study suggest that ALO suppressed migration, invasion, and adhesion in bladder cancer cells by upregulating the expression of TIMP-4.

Background: Protease inhibitors (PIs) have attracted attention due to their important roles in plant defense. Objective: The objective of this work was to characterize and evaluate the antimicrobial activity of the peptides of a family of serine PIs from Capsicum chinense Jacq. seeds. Methods: Initially, PIs were extracted from the seeds and subjected to purification by chromatography, resulting in three different peptide enriched fractions (PEFs) termed PEF1, PEF2 and PEF3. Subsequently, the PEF3 was subjected to trypsin inhibition assays, α-amylase activity assays, antimicrobial activity assays on phytopathogenic fungi, and assays to determine the likely mechanisms of action. Results: The PEF3 was composed of three protein bands with molecular masses ranging between 6 and 14 kDa. The amino acid residues of the ~6 kDa band showed high similarity with serine PIs. PEF3 inhibited the activity of the enzymes trypsin, human salivary α-amylase, and Tenebrio molitor larval α-amylase and inhibited the growth of phytopathogenic fungi, showing 83.7% loss of viability in Fusarium oxysporum. PEF3 induced reactive oxygen species in Colletotrichum lindemuthianum and F. oxysporum to dissipate their mitochondrial membrane potential and activated caspases in C. lindemuthianum. Conclusion: Our results reinforce the importance of PIs in plant defense mechanisms against phytopathogenic fungi as well as in their biotechnological applications for the control of plant pathogens.