Histidine is an essential amino acid with significant implications in human growth and neuromodulation. Its concentration within cells, when either elevated or reduced, can indicate different diseases. While various methods exist to measure increased histidine levels, there remains a significant lack of sensors capable of actively responding to histidine deficiency within cells and releasing strong signals. In this study, we exploited the high induction levels of the his operon in S. Typhimurium SL1344, a histidine auxotroph, within a histidine-deficient environment, to develop a specific bacterial sensor with sensitivity towards low histidine concentrations. The SL1344-pGEX sensor, with a high copy number, exhibited remarkable sensitivity and selectivity to histidine in the range of 0 to 50 μM. Notably, even a minute addition of histidine (approximately 2.5 μM) to the M9 medium led to observable fluorescence reduction, rendering it highly suitable for monitoring histidine-deficient cellular environments. This bacterial fluorescence sensor holds great potential for detecting changes in intracellular histidine concentrations during pathogenic bacterial infections and for assessing the impact of drugs on cellular metabolism.

High-temperature cooking process like frying, baking, smoking, or drying can induce chemical transformations in conventional food ingredients, causing deteriorative modifications. These reactions, including hydrolytic, oxidative, and thermal changes, are a common occurrence and can result in alterations to the food's chemical composition. In this study, a combination of sucrose and histidine (Su-Hi) was transformed through a process of charring or pyrolysis. The GC-MS profiling study showed that when sucrose and histidine (Su-Hi) are exposed to high temperatures (≈240°C), they produce carbonyl and aromatic compounds including beta-D-Glucopyranose, 1,6-anhydro (10.11 %), 2-Butanone, 4,4-dimethoxy- (12.89 %), 2(1H)-Quinolinone-hydrazine (5.73%), Benzenamine (6.35%), 2,5-Pyrrolidinedione, 1-[(3,4-dimethylbenzoyl)oxy]- (5.82%), Benzene-(1-ethyl-1-propenyl) (5.62%), and 4-Pyridinamine-2,6-dimethyl (5.52%). The compounds mentioned have the ability to permeate the cell membrane and contribute to the development of cell death by necrosis in human immune cells. The evidence available suggests that a specific set of pyrolytic compounds may pose a risk to immune cells. This investigation reveals the complex relationship between high-temperature cooking-induced transformations, compound permeation inside the cells, and downstream cellular responses, emphasizing the significance of considering the broader health implications of food chemical contaminants.

Accumulating evidence suggests that histamine synthesis induced in several types of tumor tissues should modulate tumor immunity. We found that a transient histamine synthesis was induced in CD11b⁺Gr-1⁺splenocytes derived from BALB/c mice transplanted with a syngeneic colon carcinoma, CT-26, when they were co-cultured with CT-26 cells. Significant levels of IFN-γ were produced under this co-culture condition. We explored the modulatory roles of histamine on IFN-γ production and found that several histamine receptor antagonists, such as pyrilamine, diphenhydramine, JNJ7777120, and thioperamide, could significantly suppress IFN-γ production. However, suppression of IFN-γ production by these antagonists was also found when splenocytes were derived from the Hdc^-/- BALB/c mice. Suppressive effects of these antagonists were found on IFN-γ production induced by concanavalin A or the combination of an anti-CD3 antibody and an anti-CD28 antibody in a histamine-independent manner. Murine splenocytes were found to express H₁ and H₂ receptors, but not H₃ and H₄ receptors. IFN-γ production in the Hh1r^-/- splenocytes induced by the combination of an anti-CD3 antibody and an anti-CD28 antibody was significantly suppressed by these antagonists. These findings suggest that pyrilamine, diphenhydramine, JNJ7777120, and thioperamide could suppress IFN-γ production in activated splenocytes in histamine-independent manner.

Bicyclic peptides have attracted the interest of pharmaceutical companies because of their remarkable properties putting them on a new path in medicine. Their conformational rigidity that improves proteolytic stability, leads to rapid penetration into tissues via any possible route of administration and elimination, occurring by renal metabolism, is of great importance for people with a history of liver diseases. In addition, each ring can function independently, making them extremely versatile molecules for further optimization. In this paper we compared the potentiometric and spectroscopic properties studied by UV-Vis, MCD, and EPR, of four synthetic analogues of the bi-cyclic peptide c(PKKHP-c(CFWKTC)-PKKH). In particular we correlated the structural and spectral properties of complexes with coordinating abilities toward Cu(II) ions of MCL (Ac-PKKHPc(CFWKTC)PKKH-NH2) that contains the unbinding cycle and N- and C-terminal linear parts, with two histidine residues, one per part; two monocyclic ligands containing one histidine residue, both in the N-terminal position i.e., MCL2 (Ac-PKKHPc(CFWKTC)PKKS-NH2) and in the C-terminal position i.e., MCL3 (Ac-PKKSPc(CFWKTC)PKKH-NH2), respectively, and the linear structure LNL (Ac-PKKHPSFWKTSPKKH-NH2).

Methicillin-resistant Staphylococcus aureus (MRSA) exerts a considerable concern in healthcare and the community. Globally MRSA strains cause numerous infections with high morbidity and mortality rates. The success of MRSA is a result of the extensive production of virulence factors. With the limited treatment options for the MRSA infection and growing resistance problem, an urgent call is needed to search for an alternative to antibiotics. One of the promising strategies is targeting the quorum sensing (QS) system, of the MRSA, by using a dendrimer loaded with kinase inhibitor peptide. This study formulates a poly-amidoamine dendrimers (PAMAM) G4 dendrimers loaded with Quorum Quencher (QQ), QQ3 peptide which is a Histidine Kinase inhibitor. The physicochemical properties of the formula were characterized using different in-vitro analysis method such as Zetasizer and transmission electron microscope (TEM). The antibacterial activity and anti-virulence effect of the formula was tested against MRSA and different mutant stains using growth assay, haemolysis assay and biofilm assay. Overall, QQ3-G4 complex showed antibacterial and anti-virulence activity and it can be a potential alternative treatment to overcome antimicrobial resistance and treat MRSA infection.

Different external stimuli are perceived by multiple sensor histidine kinases and transmitted by phosphorylation via the phosphotransfer protein Ypd1p in the multistep phosphorelay system of the high osmolarity glycerol signaling pathway of filamentous fungi. How the signal propagation takes place is still not known in detail, since multiple sensor histidine kinase genes in most filamentous fungi are coded in the genome, whereas only one gene for Ypd1 exists. That raises the hypothesis that various Ypd1 isoforms are produced from a single gene sequence, perhaps by alternative splicing, facilitating a higher variability in signal transduction. We found that the mRNA of MoYPD1 in the rice blast fungus Magnaporthe oryzae is subjected to an increased structural variation and amplified putative isoforms on a cDNA level. We then generated mutant strains overexpressing these isoforms, purified the products and present here one previously unknown MoYpd1 isoform on a proteome level. Alternative splicing was found to be a valid molecular mechanism to increase the signal diversity in eukaryotic multistep phosphorelay systems.

The group III two-component hybrid histidine kinase MoHik1p in the filamentous fungus Magnaporthe oryzae is known to be a sensor for external osmotic stress and essential for the fungicidal activity of the phenylpyrrole fludioxonil. The mode of action of fludioxonil has not yet been completely clarified but rather assumed to hyperactivate the high osmolarity glycerol (HOG) signaling pathway. To date, not much is known about the detailed molecular mechanism of how osmotic stress is detected or fungicidal activity is initiated within the HOG pathway. The molecular mechanism of signaling was studied using a mutant strain in which the HisKA signaling domain was modified by an amino acid change of histidine H736 to alanine A736. We found that MoHik1pH736A is as resistant to fludioxonil but not as sensitive to osmotic stress as the null mutant ∆Mohik1. H736 is required for fludioxonil action but is not essential for sensing sorbitol stress. Consequently, this report provides evidence of the difference in the molecular mechanism of fludioxonil action and the perception of osmotic stress. This is an excellent basis to understand the successful phenylpyrrole-fungicides’ mode of action better and will give new ideas to decipher cellular signaling mechanisms.

Copper(II), nickel(II) and zinc(II) complexes of various peptide fragments of tau protein were studied by potentiometric and spectroscopic techniques. All peptides contained one histidyl residue and represented the sequences of tau(91-97) (Ac-AQPHTEI-NH2), tau(385-390) (Ac-KTDHGA-NH2) and tau(404-409) (Ac-SPRHLS-NH2). Imidazole-N donors of histidine were the primary metal binding sites for all peptides and all metal ions but in case of copper(II) and nickel(II) the deprotonated amide groups were also involved in metal binding by increasing pH. The most stable complexes were formed with copper(II) ion but the presence of prolyl residues resulted in significant changes in the thermodynamic stability and speciation of the systems. It was also demonstrated that nickel(II) and especially zinc(II) complexes have relative low thermodynamic stability with these peptides. Copper(II) catalyzed oxidation of the peptides was also studied. In the presence of H2O2 the fragmentation of peptides can be detected in all cases. In the simultaneous presence of of H2O2 and ascorbic acid the extent of the fragmentation of the peptide is less preferred, and the formation of 2-oxo-histidine also occurs.