Protein and Peptide Letters - Volume 29, Issue 12, 2022

It has almost been 40 years since the Ras proteins were discovered as the first human oncogenes. They remain among the most important genes for regulating mammalian cell growth and are involved in more than a quarter of human cancers. Out of 167 members of the Ras superfamily, KRas mutations are the most abundant in human cancers. Particularly, the K-Ras G12C mutations are known to be involved in pancreatic, colon and lung cancers as well as leukemias. Though progress has been made, approaches targeting Ras proteins for therapeutic purposes remain challenging. No drugs treating Ras-related cancers are currently on the market. However, there is now renewed interest in the Ras area, and newer approaches have highlighted the targeting of several types of tumors and treating cancer patients. This review will summarize recent K-Ras drug candidates and approaches in the preclinical, clinical and post-clinical pipelines that show promise for targeting and reducing Ras-related tumors. Macromolecules such as mRNA vaccines, siRNA, and T-cell receptors that target Ras will also be discussed. The newer molecules and the recent approaches to be discussed suggest that the “undruggable” era of Ras proteins could be coming to an end.

Gut peptides are small peptides secreted by gut endocrine cells that can modulate the roles and functions of different organs through signaling. Gut peptides can also majorly impact the body’s energy homeostasis by regulating appetite and energy metabolism. The gut-brain axis (GBA) is bidirectional communication between the central nervous system (CNS) and the peripheral enteric nervous system. The regulation of appetite acts by hypothalamic neuronal activity. The complex interaction of hedonic and homeostatic factors implicates appetite regulation. In the CNS, the hypothalamus and brainstem have a dominating role in appetite regulation. The arcuate nucleus (ARC) of the hypothalamus plays a vital role in energy homeostasis, while other nuclei also play a role in appetite regulation. The gut conveys peripheral information about energy balance to the brain via gut peptides and receptors for the digestion of food. The varied gut peptides have different actions on appetite regulation.

Isocitrate lyase (ICL), an enzyme of the glyoxylate shunt pathway, is essential for the virulence and persistence of dreaded Mycobacterium tuberculosis (Mtb) in its host. This pathway, along with the methylcitrate cycle, facilitates the utilization of fatty acids as a carbon source inside hostile host environments such as in granulomas, and hence enzymes of this pathway are novel antitubercular targets. The genome sequence of pathogenic Mtb H37Rv presents three ICLs annotated as Rv0467 (prokaryotic homologue), Rv1915 and Rv1916. The latter two, Rv1915 and Rv1916, together constitute the longer version of ICL2, a eukaryotic counterpart. Despite being a well-known drug target, no Mtb ICL inhibitor has reached clinical trials due to challenges associated with targeting all the 3 orthologs. This gap is the result of uncharacterized Rv1915 and Rv1916. This review aims to appreciate chronologically the key studies that have built our comprehension of Mtb ICLs. Recently characterized Mtb Rv1915 and Rv1916, which further open venues for developing effective inhibitors against the persistent and drug-resistant Mtb, are discussed separately.

Background: Hepatic encephalopathy (HE) is a neuropsychiatric syndrome that involves cognitive and motor dysfunctions due to hepatic failure. The clinical and experimental studies suggest that the angiotensin (Ang) converting enzyme (ACE), Ang II, and angiotensin type 1 receptor (AT1R), which compose the classical pathway of the renin–angiotensin system (RAS), exacerbate neuroinflammation in different neurologic diseases. Conversely, Ang-(1-7), ACE2, and Mas receptor, which integrate the alternative RAS axis, have been shown as promising therapeutic targets in neuropsychiatric disorders, leading to neuroprotection. Objective: This study aimed to investigate the potential participation of the RAS components in thioacetamide (TAA)-induced HE in mice. Methods: We also evaluated the levels of neurotrophic factors, pro-inflammatory cytokines, and chemokine in the central nervous system of TAA-induced HE in mice. Mice were submitted to acute liver failure induced by TAA administration by intraperitoneal route. Measurements of RAS components (ACE, Ang II, ACE2 and Ang1-7) and neurotrophic factors (BDNF, GDNF and NGF) were obtained by ELISA assay. Pro-inflammatory cytokines (TNF, IFN-γ, IL-6, IL-12p70) and the chemokine (CCL2) were quantified by cytometric bead array. The student’s t-test was applied for statistical analysis. Results: Mice presented increased cortical levels of ACE, while Ang-(1-7) levels were decreased in cortical and hippocampal samples compared to controls. Moreover, HE mice had an increase in the Ang II/Ang-(1-7) ratio along with reduced levels of neural growth factor (NGF) in the prefrontal cortex. They also showed elevated levels of IFN-γ and CCL2 in the prefrontal cortex and of TNF, IL-6, IL-12, and CCL2 in the hippocampus compared with controls. Conclusion: This study suggested that the reduction of components of the alternative RAS axis was associated with the deleterious effects of neuroinflammation and lower neuroprotective effects of NGF during TAA-induced HE.

Objective: The work aimed to compare the binding between the two main components of Polygala tenuifolia Willd. and two cholinesterases (ChEs) by using a variety of spectral techniques. Methods: Two main components of Polygala tenuifolia Willd. included Tenuifolin (Ten) and Onjisaponin B (Onj B), and two ChEs included acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Results: The UV-visible absorption spectra results showed that Ten had no effect on the structure of ChEs, and the combination of Onj B with ChEs changed its structure. Onj B statically quenched the endogenous fluorescence of both of ChEs, Ten dynamically quenched the endogenous fluorescence of AChE with no effect on BChE. The fluorescence quenching rate of ChEs by Onj B was much higher than that of AChE by Ten, and only one binding site of each protein spontaneously interacted with the compound to bind to or collide. Synchronous fluorescence results showed that Ten and Onj B quenched the fluorescence intensity by affecting tryptophan and tyrosine residues in cholinesterases, respectively. Hydrophobic force played an important role in the interaction between Ten and AChE, and van der Waals force and hydrogen bond were the main driving forces for the binding of Onj B to ChEs. The Enzyme activity test showed that Onj B inhibited ChE activity, and Ten never inhibited ChE activity. Conclusion: Onj B has the potential to inhibit ChE activity and increase the neurotransmitter acetylcholine content in the nerve system, improving the Alzheimer's disease (AD).

Platycodon grandiflorus is a well-known and widely distributed traditional herbal medicine and functional food in Asia, with triterpenoids as the main bioactive component in its roots. Acetyl-CoA C-acetyltransferase (AACT) is the initiation enzyme in the mevalonate pathway and plays an important role in the biosynthesis of terpenoids. Objective: The objective of this study was to clone and identify the PgAACT function in P. grandiflorus. Methods: The full-length sequence of PgAACT genes was isolated and cloned from P. grandiflorus by polymerase chain reaction (PCR). The recombinant plasmid was constructed using the pET-32a vector and expressed in E. coli Transetta (DE3) cells. Subcellular localization of AACT was observed in the epidermal cells of N. tabacum. Quantitative reverse transcription-PCR (qRT-PCR) was used to identify the PgAACT gene transcription levels. After MeJA treatment, the changes in AACT gene expression were observed, and UHPLC-Q-Exactive Orbitrap MS/MS was used to detect the changes in P. grandiflorus saponins. Results: In this study, two full-length cDNAs encoding AACT1 (PgAACT1) and AACT2 (PgAACT2) were isolated and cloned from P. grandiflorus. The deduced PgAACT1 and PgAACT2 proteins contain 408 and 416 amino acids, respectively. The recombinant vectors were constructed, and the protein expression was improved by optimizing the reaction conditions. Sodium dodecyl sulphate-polycrylamide gel electrophloresis and western blot analysis showed that the PgAACT genes were successfully expressed, with molecular weights of the recombinant proteins of 61 and 63 kDa, respectively. Subcellular localization showed that the PgAACT genes were localized in the cytoplasm. Tissue specificity analysis of P. grandiflorus from different habitats showed that PgAACT genes were expressed in the roots, stems, and leaves. After MeJA treatment, the expression level of PgAACT genes and the content of total saponins of P. grandiflorus were significantly increased, suggesting that PgAACT genes play an important role in regulating plant defense systems. Conclusion: Cloning, expression, and functional analysis of PgAACT1 and PgAACT2 will be helpful in understanding the role of these two genes in terpene biosynthesis.

Background: Accumulating evidence has demonstrated the immunomodulatory effects of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in rheumatoid arthritis and the tumor microenvironment, besides its known capacity of specifically inducing the apoptosis of cancer cells. Mice are common available animal models for studying the roles of TRAIL. However, mice express only a single TRAIL receptor (mTRAILR) with an intracellular death domain, in contrast to the two TRAIL receptors (TRAILR1 and TRAILR2) in humans. Moreover, human TRAIL binds weakly to mTRAILR, whereas mouse TRAIL has a high affinity for human TRAIL-Rs. Therefore, we considered that murine TRAIL would be more suitable than human TRAIL for exploring the immunoregulatory effect of TRAIL in immunocompetent mice or when using mouse cells as the target. To our knowledge, the detailed method for the production of recombinant murine TRAIL has not been reported. Objective: In this study, we aimed to design and express two soluble forms of murine TRAIL and verify the properties of the protein. Methods: Recombinant murine TRAILs were expressed in Escherichia coli BL21 (DE3, and Nichelating affinity chromatography was used for protein purification. SDS-PAGE, GDS-PAGE and HPLC were applied to analyze the protein structure. The cytotoxicity of our purified murine TRAILs was evaluated in the TRAIL-sensitive human breast cancer ZR-75-30 cells and murine breast cancer 4T1 cells. Finally, validation of the tumor-killing ability of the murine protein in vivo. Results: Two soluble forms of murine TRAILs (mT_N99 and mT_N188) were purified and demonstrated with high purity and trimeric structure. In addition, Zn²⁺ supplement was essential to produce soluble murine TRAILs in E.coli BL21 (DE3). The two purified soluble mTRAILs showed similar cytotoxicity to cancer cells, moreover, mT_N99 also showed a good anti-tumor effect in vivo and is more suitable for the treatment of murine tumor models. Conclusion: A production approach for recombinant murine TRAIL was determined, which covered the design of shortened forms, expression, purification and characterization.

Background: Previously, AF-956, which contains S356 of FAM83G and an N-terminal antenna peptide for entry into colon cancer cells, is markedly antiproliferative compared to a control peptide (AF-859), which lacks the N-terminal antenna peptide, by inducing apoptosis via the inhibition of HSP27 phosphorylation at residues S15 and S82. Objective: Because FAM83G-derived peptides are promising lead compounds for colon cancer treatment, we reanalyzed the effect of AG-066, which contains S356 of FAM83G and an N-terminal antenna peptide for entry into the liver cancer cells. Methods: HepG2 liver cancer cells were incubated with either AF-859 or AG-066 at a concentration of 54 μM at 37 °C for 24, 48, and 72 h. The effects of AF-859 and AG-066 on the cultured HepG2 cells were estimated using an inverted light microscope. Furthermore, the DNA ladder method and the dead cell assay were performed by applying Live/Dead Cell Staining Kit II. Erk phosphorylation was estimated by western blotting. Results: Treatment with AG-066 markedly reduced HepG2 viable cell counts compared to the AF- 859-treated HepG2 cells, as evident from the significantly increased number of dead cells in the culture medium. Additionally, AG-066 treatment increased cellular DNA laddering. We found no difference in Erk phosphorylation status between the AG-066- and AF-859-treated groups. Conclusion: This study illustrated that the peptide with a structure based on FAM83G functions as a spontaneous apoptosis inducer for liver cancer cells. Hence, it is a promising lead compound for the treatment of liver cancer.

Background: Fungal and parasitic diseases are global health problems, and the available treatments are becoming ineffective, mainly due to the emergence of resistant strains of pathogens. Furthermore, the drugs currently in use exhibit high toxicity and side effects. The scarcity of efficient treatments for fungal and parasitic diseases has motivated the search for new drug candidates, including antimicrobial peptides. The chemokine class RP1 peptide shows inhibitory activity against bacteria, viruses, cancer cells and parasites. In addition, the organometallic compound ferrocene showed antiparasitic activity. Objective: Study aimed to assess the effect of conjugation of the RP1 peptide with ferrocene in terms of its structure, biological activity against fungi and parasites and toxicity. Methods: Peptides and conjugates were synthesized using solid phase peptide synthesis (SPPS). The Fc-RP1 peptide showed antifungal and antimalarial activities with low toxicity in the U87 and HepG2 cell lines. Results: The mechanism of action of these peptides, analyzed by flow cytometry in the fungus Cryptococcus neoformans, was through membrane permeabilization, with an emphasis on the Fc-RP1 peptide that presented the highest rate of PI-positive cell marking. Conclusion: In conclusion, ferrocene conjugated to antimicrobial peptide RP1 is an attractive biomolecule for drug discovery against fungal and parasitic diseases.

Background: The ionic interactions play an important role in the stabilization of the native conformation of proteins. Toxoplasma gondii Ferredoxin NADP+ Reductase (TgFNR) remains stable at pH 4.0. However, such modulation of ionic interactions leads to compaction and non-cooperativity in its folding. Objective: To gain insights into the role of ionic interactions in the modulation of structure and thermodynamic stability of TgFNR. Methods: Protein preparations, circular dichroism and fluorescence spectroscopy were used to determine salt-induced changes in the structure and stability of TgFNR. Results: The kosmotropic salts (sodium fluoride and sodium sulphate) appear to induce the biphasic response on the structure and stability of TgFNR. At pH about 4.0, the addition of low concentrations of kosmotropic salts significantly perturbs the existing native-like secondary structure of TgFNR, whereas higher quantities of salt reversed the denaturing impact. This is a one-of-a-kind situation we are unaware of in any other protein. The urea-induced unfolding of TgFNR in the presence of a low dose of salt (100 mM) drastically affected the protein's thermodynamic stability at neutral pH. The increased salt concentrations, on the other hand, reversed the destabilizing effect. Conclusion: Our findings imply that electrostatic interactions are exceptionally significant for the TgFNR stability, however, render highly unusual behavior of Hofmeister series salts, indicating a possible crucial role of salt bridges in the stabilization of different conformations of the protein.