Journal of Inorganic Biochemistry最新文献

The dyshomeostasis of metal ions in the brain leads to the accumulation of excess metals in extracellular and inter-neuronal locations and the Amyloid β peptide (Aβ) binds these transition metals, which ultimately cause the Aβ aggregation and severe oxidative stress in the brain. The aggregation of Aβ and oxidative stress are important factors to trigger Alzheimer's disease (AD). Metal chelation therapy is a promising approach to removing metals from Aβ-M species and relieve the oxidative stress. Therefore, 4 tetrahydrosalens containing benzothiazole moiety were designed and synthesized. Their biological activities for Alzheimer's disease therapy in vitro were determined by Turbidity assay, BCA protein assay, MTT assay and fluorescent probe of DCFH-DA. The results were comparing with that of non-specific chelator (cliquinol, CQ) and non-benzothiazole functionalized tetrahydrosalens, the results demonstrated that benzothiazole functionalized chelators had more efficient bio-activities in preventing Cu²⁺-induced Aβ aggregation, attenuating cytotoxicity mediated by Aβ-Cu²⁺ species and decrease the level of reactive oxygen species (ROS) in Cu²⁺-Aβ treated PC12 cells than that of cliquinol and non-benzothiazole functionalized analogues.

Halogenation of aliphatic C–H bonds is a chemical transformation performed in nature by mononuclear nonheme iron dependent halogenases. The mechanism involves the formation of an iron(IV)-oxo-chloride species that abstracts the hydrogen atom from the reactive C–H bond to form a carbon-centered radical that selectively reacts with the bound chloride ligand, a process commonly referred to as halide rebound. The factors that determine the halide rebound, as opposed to the reaction with the incipient hydroxide ligand, are not clearly understood and examples of well-defined iron(IV)-oxo-halide compounds competent in C–H halogenation are scarce. In this work we have studied the reactivity of three well-defined iron(IV)-oxo complexes containing variants of the tetradentate 1-(2-pyridylmethyl)-1,4,7-triazacyclononane ligand (Pytacn). Interestingly, these compounds exhibit a change in their chemoselectivity towards the functionalization of C–H bonds under certain conditions: their reaction towards C–H bonds in the presence of a halide anionleads to exclusive oxygenation, while the addition of a superacid results in halogenation. Almost quantitative halogenation of ethylbenzene is observed when using the two systems with more sterically congested ligands and even the chlorination of strong C–H bonds such as those of cyclohexane is performed when a methyl group is present in the sixth position of the pyridine ring of the ligand. Mechanistic studies suggest that both reactions, oxygenation and halogenation, proceed through a common rate determining hydrogen atom transfer step and the presence of the acid dictates the fate of the resulting alkyl radical towards preferential halogenation over oxygenation.

Over the last 50 years resonance Raman spectroscopy has become an invaluable tool for the exploration of chromophores in biological macromolecules. Among them, heme proteins and metal complexes have attracted considerable attention. This interest results from the fact that resonance Raman spectroscopy probes the vibrational dynamics of these chromophores without direct interference from the surrounding. However, the indirect influence via through-bond and through-space chromophore-protein interactions can be conveniently probed and analyzed. This review article illustrates this point by focusing on class 1 cytochrome c, a comparatively simple heme protein generally known as electron carrier in mitochondria. The article demonstrates how through selective excitation of resonance Raman active modes information about the ligation, the redox state and the spin state of the heme iron can be obtained from band positions in the Raman spectra. The investigation of intensities and depolarization ratios emerged as tools for the analysis of in-plane and out-of-plane deformations of the heme macrocycle. The article further shows how resonance Raman spectroscopy was used to characterize partially unfolded states of oxidized cytochrome c. Finally, it describes its use for exploring structural changes due to the protein's binding to anionic surfaces like cardiolipin containing membranes.

The Preyssler-type polyoxotungstate ({P₅W₃₀}) belongs to the family of polyanionic metal-oxides formed by group V and VI metal ions, such as V, Mo and W, commonly known as polyoxometalates (POMs). POMs have demonstrated inhibitory effect on a significant number of ATP-binding proteins in vitro. Purinergic P2 receptors, widely expressed in eukaryotic cells, contain extracellularly oriented ATP-binding sites and play many biological roles with health implications. In this work, we use the immortalized mouse hippocampal neuronal HT-22 cells in culture to study the effects of {P₅W₃₀} on the cytosolic Ca²⁺ concentration. Changes in cytosolic Ca²⁺ concentration were monitored using fluorescence microscopy of HT-22 cells loaded with the fluorescent Ca²⁺ indicator Fluo3. ³¹P-Nuclear magnetic resonance measurements of {P₅W₃₀} indicate its stability in the medium used for cytosolic Ca²⁺ measurements for over 30 min. The findings reveal that addition of {P₅W₃₀} to the extracellular medium induces a sustained increase of the cytosolic Ca²⁺ concentration within minutes. This Ca²⁺ increase is triggered by extracellular Ca²⁺ entry into the cells and is dose-dependent, with a half-of-effect concentration of 0.25 ± 0.05 μM {P₅W₃₀}. In addition, after the {P₅W₃₀}-induced cytosolic Ca²⁺ increase, the transient Ca²⁺ peak induced by extracellular ATP is reduced up to 100% with an apparent half-of-effect concentration of 0.15 ± 0.05 μM {P₅W₃₀}. Activation of metabotropic purinergic P2 receptors affords about 80% contribution to the increase of Fluo3 fluorescence elicited by {P₅W₃₀} in HT-22 cells, whereas ionotropic receptors contribute, at most, with 20%. These results suggest that {P₅W₃₀} could serve as a novel agonist of purinergic P2 receptors.

Recent structural and biophysical studies of O₂-sensing FixL, NO-sensing soluble guanylate cyclase, and other biological heme-based sensing proteins have begun to reveal the details of their molecular mechanisms and shed light on how nature regulates important biological processes such as nitrogen fixation, blood pressure, neurotransmission, photosynthesis and circadian rhythm. The O₂-sensing FixL protein from S. meliloti, the eukaryotic NO-sensing protein sGC, and the CO-sensing CooA protein from R. rubrum transmit their biological signals through gas-binding to the heme domain of these proteins, which inhibits or activates the regulatory, enzymatic domain. These proteins appear to propagate their signal by specific structural changes in the heme sensor domain initiated by the appropriate gas binding to the heme, which is then propagated through a coiled-coil linker or other domain to the regulatory, enzymatic domain that sends out the biological signal. The current understanding of the signal transduction mechanisms of O₂-sensing FixL, NO-sensing sGC, CO-sensing CooA and other biological heme-based gas sensing proteins and their mechanistic themes are discussed, with recommendations for future work to further understand this rapidly growing area of biological heme-based gas sensors.

Two copper(II) complexes containing diplacone (H₄dipl), a naturally occurring C-geranylated flavanone derivative, in combination with bathophenanthroline (bphen) or 1,10-phenanthroline (phen) with the composition [Cu₃(bphen)₃(Hdipl)₂]⋅2H₂O (1) and {[Cu(phen)(H₂dipl)₂]⋅1.25H₂O}_n (2) were prepared and characterized. As compared to diplacone, the complexes enhanced in vitro cytotoxicity against A2780 and A2780R human ovarian cancer cells (IC₅₀ ≈ 0.4–1.2 μM), human lung carcinoma (A549, with IC₅₀ ≈ 2 μM) and osteosarcoma (HOS, with IC₅₀ ≈ 3 μM). Cellular effects of the complexes in A2780 cells were studied using flow cytometry, covering studies concerning cell-cycle arrest, induction of cell death and autophagy and induction of intracellular ROS/superoxide production. These results uncovered a possible mechanism of action characterized by the G2/M cell cycle arrest. The studies on human endothelial cells revealed that complexes 1 and 2, as well as their parental compound diplacone, do possess anti-inflammatory activity in terms of NF-κB inhibition. As for the effects on PPARα and/or PPARγ, complex 2 reduced the expression of leukocyte adhesion molecules VCAM-1 and E-selectin suggesting its dual anti-inflammatory capacity. A wide variety of Cu-containing coordination species and free diplacone ligand were proved by mass spectrometry studies in water-containing media, which might be responsible for multimodal effect of the complexes.

Manganese hydroxido (Mn–OH) complexes supported by a tripodal N,N′,N″-[nitrilotris(ethane-2,1-diyl)]tris(P,P-diphenylphosphinic amido) ([poat]³⁻) ligand have been synthesized and characterized by spectroscopic techniques including UV–vis and electron paramagnetic resonance (EPR) spectroscopies. X-ray diffraction (XRD) methods were used to confirm the solid-state molecular structures of {Na₂[Mn^IIpoat(OH)]}₂ and {Na[Mn^IIIpoat(OH)]}₂ as clusters that are linked by the electrostatic interactions between the sodium counterions and the oxygen atom of the ligated hydroxido unit and the phosphinic (P=O) amide groups of [poat]³⁻. Both clusters feature two independent monoanionic fragments in which each contains a trigonal bipyramidal Mn center that is comprised of three equatorial deprotonated amide nitrogen atoms, an apical tertiary amine, and an axial hydroxido ligand. XRD analyses of {Na[Mn^IIIpoat(OH)]}₂ also showed an intramolecular hydrogen bonding interaction between the Mn^III–OH unit and P=O group of [poat]³⁻. Crystalline {Na[Mn^IIIpoat(OH)]}₂ remains as clusters with Na⁺---O interactions in solution and is unreactive toward external substrates. However, conductivity studies indicated that [Mn^IIIpoat(OH)]⁻ generated in situ is monomeric and reactivity studies found that it is capable of cleaving C-H bonds, illustrating the importance of solution-phase speciation and its direct effect on chemical reactivity.

Synopsis: Manganese–hydroxido complexes were synthesized to study the influence of H-bonds in the secondary coordination sphere and their effects on the oxidative cleavage of substrates containing C-H bonds.

Aminophenol dioxygenases (APDO) are mononuclear nonheme iron enzymes that utilize dioxygen (O₂) to catalyze the conversion of o-aminophenols to 2-picolinic acid derivatives in metabolic pathways. This study describes the synthesis and O₂ reactivity of two synthetic models of substrate-bound APDO: [Fe^II(Tp^Me2)(^tBu2APH)] (1) and [Fe^II(Tp^Me2)(^tBuAPH)] (2), where Tp^Me2 = hydrotris(3,5-dimethylpyrazole-1-yl)borate, ^tBu2APH = 4,6-di-tert-butyl-2-aminophenolate, and ^tBuAPH₂ = 4-tert-butyl-2-aminophenolate. Both Fe(II) complexes behave as functional APDO mimics, as exposure to O₂ results in oxidative CC bond cleavage of the o-aminophenolate ligand. The ring-cleaved products undergo spontaneous cyclization to give substituted 2-picolinic acids, as verified by ¹H NMR spectroscopy, mass spectrometry, and X-ray crystallography. Reaction of the APDO models with O₂ at low temperature reveals multiple intermediates, which were probed with UV–vis absorption, electron paramagnetic resonance (EPR), Mössbauer (MB), and resonance Raman (rRaman) spectroscopies. The most stable intermediate at −70 °C in THF exhibits multiple isotopically-sensitive features in rRaman samples prepared with ¹⁶O₂ and ¹⁸O₂, confirming incorporation of O₂-derived atom(s) into its molecular structure. Insights into the geometric structures, electronic properties, and spectroscopic features of the observed intermediates were obtained from density functional theory (DFT) calculations. Although functional APDO models have been previously reported, this is the first time that an oxygenated ligand-based radical has been detected and spectroscopically characterized in the ring-cleaving mechanism of a relevant synthetic system.

Bacteria use the second messenger cyclic dimeric guanosine monophosphate (c-di-GMP) to control biofilm formation and other key phenotypes in response to environmental signals. Changes in oxygen levels can alter c-di-GMP signaling through a family of proteins termed globin coupled sensors (GCS) that contain diguanylate cyclase domains. Previous studies have found that GCS diguanylate cyclase activity is controlled by ligand binding to the heme within the globin domain, with oxygen binding resulting in the greatest increase in catalytic activity. Herein, we present evidence that heme-edge residues control O₂-dependent signaling in PccGCS, a GCS protein from Pectobacterium carotovorum, by modulating heme distortion. Using enzyme kinetics, resonance Raman spectroscopy, small angle X-ray scattering, and multi-wavelength analytical ultracentrifugation, we have developed an integrated model of the full-length PccGCS tetramer and have identified conformational changes associated with ligand binding, heme conformation, and cyclase activity. Taken together, these studies provide new insights into the mechanism by which O₂ binding modulates activity of diguanylate cyclase-containing GCS proteins.

Wet synthesis approach afforded four new heteroleptic mononuclear neutral diamagnetic oxidovanadium(V) complexes, comprising salicylaldehyde-based 2-furoic acid hydrazones and a flavonol coligand of the general composition [VO(fla)(L-ONO)]. The complexes were comprehensively characterized, including chemical analysis, conductometry, infrared, electronic, and mass spectroscopy, as well as 1D ¹H and proton-decoupled ¹³C(¹H) NMR spectroscopy, alongside extensive 2D ¹H¹H COSY, ¹H¹³C HMQC, and ¹H¹³C HMBC NMR analyses. Additionally, the quantum chemical properties of the complexes were studied using Gaussian at the B3LYP, HF, and M062X levels on the 6–31++g(d,p) basis sets. The interaction of these hydrolytically inert vanadium complexes and the BSA was investigated through spectrofluorimetric titration, synchronous fluorimetry, and FRET analysis in a temperature-dependent manner, providing valuable thermodynamic insights into van der Waals interactions and hydrogen bonding. Molecular docking was conducted to gain further understanding of the specific binding sites of the complexes to BSA. Complex 2, featuring a 5-chloro-substituted salicylaldehyde component of the hydrazone, was extensively examined for its biological activity in vivo. The effects of complex administration on biochemical and hematological parameters were evaluated in both healthy and diabetic Wistar rats, revealing antihyperglycemic activity at millimolar concentration. Furthermore, histopathological analysis and bioaccumulation studies of the complex in the brain, kidneys, and livers of healthy and diabetic rats revealed the potential for further development of vanadium(V) hydrazone complexes as antidiabetic and insulin-mimetic agents.