The Reaction of Arsenite with Proteins Relies on Solution Conditions

Molybdenum trioxide as a newer diversified economic catalyst for the transformation of nitroarenes to arylamine and 5-substituted-1H-tetrazole

The present work has developed a straightforward, gentle, and effective approach for synthesizing arylamines and 5-substituted-1H-tetrazole derivatives, and among the two tested catalysts, molybdenum trioxide (MoO3) proved to be highly effective. The selective hydrogenation of nitroarenes to arylamines presents a significant challenge due to the complex reaction mechanism and the competitive hydrogenation of other reducible functional groups. It facilitated the transfer hydrogenation of nitrobenzene using hydrazine hydrate-produced amino compounds and enabled the [3 + 2] cycloaddition of sodium azide with aromatic nitriles to yield 5-substituted-1H-tetrazoles. The structure of compound 5-(4-bromophenyl)-1H-tetrazole (5k) was verified through single-crystal X-ray analysis, and the calculation of Green Chemistry Metrics showed the optimal range. Notably, the MoO3 catalyst can be reutilized for up to seven cycles with minimal loss of effectiveness. These attributes make molybdenum trioxide particularly attractive for industrial applications. This methodology offers several advantages over traditional synthetic methods.

Dual role of arsenite in hydrolysis and post-hydrolysis fluorescence sensing of selective pH-dependent probes

In comparison to the sensing activity, the reactivity of arsenite (AsO2-) is less explored. Herein, we focused on AsO2- reactivity studies based on its pKa and compared the study with other common anions. All three pKa values of arsenite are >9.0, affording a flexible working pH range to design a probe for reactivity studies. We designed and synthesized six pH dependent benzothiazole-based Schiff bases, namely, 1-(((6-nitrobenzo[d]thiazol-2-yl)imino)methyl)naphthalen-2-ol (1), 5-(diethylamino)-2-(((6-nitrobenzo[d]thiazol-2-yl)imino)methyl)phenol (2), 9-(((6-nitrobenzo[d]thiazol-2-yl)imino)methyl)-2,3,6,7-tetrahydro-1H,5H-pyrido[3,2,1-ij]quinolin-8-ol (3), 5-methoxy-2-(((6-nitrobenzo[d]thiazol-2-yl)imino)methyl)phenol (4), 4-(((6-nitrobenzo[d]thiazol-2-yl)imino)methyl)benzene-1,3-diol (5), and 2-(((6-nitrobenzo[d]thiazol-2-yl)imino)methyl)phenol (6), as probes for hydrolysis studies containing 5% water in acetonitrile. In spite of the presence of water in the solution, no hydrolysis was observed for all the probes in the absence of a salt. In the presence of selected sodium salts of various anions in solution, intramolecular charge transfer (ICT) was observed after the deprotonation of an aromatic hydroxy group at the ortho position with respect to the imine groups within the probes. Among the studied anions, selective AsO2- induced imine hydrolysis was observed for probes 1 and 4. In the case of 5 with both o- and p-hydroxy groups, no hydrolysis was observed in the presence of AsO2-. Probe 6 with only the o-hydroxy group showed very fast hydrolysis with poor selectivity. The p-hydroxy group in 4-(((6-nitrobenzo[d]thiazol-2-yl)imino)methyl)phenol (7) resulted in poor AsO2- induced hydrolysis. The aldehyde, which was generated after hydrolysis of probe 1, showed selective emission at 450 nm in the presence of AsO2-. The time dependent hydrolysis reaction of probe 1 controls the emission intensity enhancement.

SsCox17, a copper chaperone, is required for pathogenic process and oxidative stress tolerance of Sclerotinia sclerotiorum

Stem rot, caused by Sclerotinia sclerotiorum has emerged as one of the major fungal pathogens of oilseed Brassica across the world. The pathogenic development is exquisitely dependent on reactive oxygen species (ROS) modulation. Cox17 is a crucial factor that shuttles copper ions from the cytosol to the mitochondria for the cytochrome c oxidase (CCO) assembly. Currently, no data is available regarding the impact of Cox17 in fungal pathogenesis. The present research was carried out to functionally characterize the role of Cox17 in S. sclerotiorum pathogenesis. SsCox17 transcripts showed high expression levels during inoculation on rapeseed. Intramitochondrial copper content and CCO activity were decreased in SsCox17 gene-silenced strains. The SsCox17 gene expression was up-regulated in the hyphae under oxidative stress and a deficiency response to oxidative stress was detected in SsCox17 gene-silenced strains. Compared to the S. sclerotiorum wild-type strain, there was a concomitant reduction in the virulence of SsCox17 gene-silenced strains. The SsCox17 overexpression strain was further found to increase copper content, CCO activity, tolerance to oxidative stress and virulence. We also observed a certain correlation of appressoria formation and SsCox17. These results provide evidence that SsCox17 is positively associated with fungal virulence and oxidative detoxification.

Arsenic-protein interactions as a mechanism of arsenic toxicity

Millions of people worldwide are exposed to arsenic, a metalloid listed as one of the top chemical pollutants of concern to human health. Epidemiological and experimental studies link arsenic exposure to the development of cancer and other diseases. Several mechanisms have been proposed to explain the effects induced by arsenic. Notably, arsenic and its metabolites interact with proteins by direct binding to individual cysteine residues, cysteine clusters, zinc finger motifs, and RING finger domains. Consequently, arsenic interactions with proteins disrupt the functions of proteins and may lead to the development and progression of diseases. In this review, we focus on current evidence in the literature that implicates the interaction of arsenic with proteins as a mechanism of arsenic toxicity. Data show that arsenic-protein interactions affect multiple cellular processes and alter epigenetic regulation, cause endocrine disruption, inhibit DNA damage repair mechanisms, and deregulate gene expression, among other adverse effects.

Molecular basis for chirality-regulated Aβ self-assembly and receptor recognition revealed by ion mobility-mass spectrometry

Despite extensive efforts on probing the mechanism of Alzheimer’s disease (AD) and enormous investments into AD drug development, the lack of effective disease-modifying therapeutics and the complexity of the AD pathogenesis process suggest a great need for further insights into alternative AD drug targets. Herein, we focus on the chiral effects of truncated amyloid beta (Aβ) and offer further structural and molecular evidence for epitope region-specific, chirality-regulated Aβ fragment self-assembly and its potential impact on receptor-recognition. A multidimensional ion mobility-mass spectrometry (IM-MS) analytical platform and in-solution kinetics analysis reveal the comprehensive structural and molecular basis for differential Aβ fragment chiral chemistry, including the differential and cooperative roles of chiral Aβ N-terminal and C-terminal fragments in receptor recognition. Our method is applicable to many other systems and the results may shed light on the potential development of novel AD therapeutic strategies based on targeting the D-isomerized Aβ, rather than natural L-Aβ.

Chiral inversion of amino acids is thought to modulate the structure and function of amyloid beta (Aβ) but these processes are poorly understood. Here, the authors develop an ion mobility-mass spectrometry based approach to study chirality-regulated structural features of Aβ fragments and their influence on receptor recognition.

A dual functional ruthenium arene complex induces differentiation and apoptosis of acute promyelocytic leukemia cells

A dual functional ruthenium arene complex induces differentiation and apoptosis of acute promyelocytic leukemia cells through degradation of PML–RARα and DNA damage.

Human acute promyelocytic leukemia (APL) is the most malignant form of acute leukemia. The fusion of PML and RARα genes is responsible for over 98% of cases of APL. In this work, we found that a Ru(ii) arene complex, [(η⁶-p-bip)Ru(en)Cl][PF₆] (Ru-1), can selectively react with PML, leading to zinc-release and protein unfolding. Consequently, the degradation of the fusion protein PML–RARα occurs, which causes the differentiation of APL cells. In addition, Ru-1 can also bind to DNA and trigger apoptosis of APL cells. Therefore, Ru-1 acts as a dual functional agent that inhibits the growth of APL cells and induces cell differentiation. In contrast, the other non-selective Ru(ii) compound, though also highly reactive to PML, does not exhibit anti-APL activity. The selectivity of Ru-1 to PML suggests a new strategy for the development of anti-APL drugs using ruthenium agents.

Arsenic trioxide preferentially binds to the ring finger protein PML: understanding target selection of the drug

Arsenic trioxide (ATO) is used in the clinic for the treatment of acute promyelocytic leukemia by targeting the protein PML. However, many zinc-finger proteins could also be reactive to arsenic in cells. Here we found that ATO preferentially binds to the ring-finger domain of PML in a protein mixture with zinc-finger domains. These results provide the molecular basis of the target selection of ATO in cells.

Arsenic trioxide inhibits liver cancer stem cells and metastasis by targeting SRF/MCM7 complex

Hepatocellular carcinoma (HCC) has a high mortality rate due to the lack of effective treatments and drugs. Arsenic trioxide (ATO), which has been proved to successfully treat acute promyelocytic leukemia (APL), was recently reported to show therapeutic potential in solid tumors including HCC. However, its anticancer mechanisms in HCC still need further investigation. In this study, we demonstrated that ATO inhibits tumorigenesis and distant metastasis in mouse models, corresponding with a prolonged mice survival time. Also, ATO was found to significantly decrease the cancer stem cell (CSC)-associated traits. Minichromosome maintenance protein (MCM) 7 was further identified to be a potential target suppressed dramatically by ATO, of which protein expression is increased in patients and significantly correlated with tumor size, cellular differentiation, portal venous emboli, and poor patient survival. Moreover, MCM7 knockdown recapitulates the effects of ATO on CSCs and metastasis, while ectopic expression of MCM7 abolishes them. Mechanistically, our results suggested that ATO suppresses MCM7 transcription by targeting serum response factor (SRF)/MCM7 complex, which functions as an important transcriptional regulator modulating MCM7 expression. Taken together, our findings highlight the importance of ATO in the treatment of solid tumors. The identification of SRF/MCM7 complex as a target of ATO provides new insights into ATO’s mechanism, which may benefit the appropriate use of this agent in the treatment of HCC.

The Effect of Salts in Promoting Specific and Competitive Interactions between Zinc Finger Proteins and Metals

Specific protein-metal interactions (PMIs) fulfill essential functions in cells and organic bodies, and activation of these functions in vivo are mostly modulated by the complex environmental factors, including pH value, small biomolecules, and salts. Specifically, the role of salts in promoting specific PMIs and their competition among various metals has remained untapped mainly due to the difficulty to distinguish nonspecific PMIs from specific PMIs by classic spectroscopic techniques. Herein, we report Hofmeister salts differentially promote the specific PMIs by combining nanoelectrospray ionization mass spectrometry and spectroscopic techniques (fluorescence measurement and circular dichroism). Furthermore, to explore the influence of salts in competitive binding between metalloproteins and various metals, we designed a series of competitive experiments and applied to a well-defined model system, the competitive binding of zinc (II) and arsenic (III) to holo-promyelocytic leukemia protein (PML). These experiments not only provided new insights at the molecular scale as complementary to previous NMR and spectroscopic results, but also deduced the relative binding ability between zinc finger proteins and metals at the molecular scale, which avoids the mass spectrometric titration-based determination of binding constants that is frequently affected and often degraded by variable solution conditions including salt contents. Graphical Abstract ᅟ.

Copper-finger protein of Sp1: the molecular basis of copper sensing

The cellular copper level is strictly regulated since excessive copper is harmful to cells. It has been proposed that the expression of copper transport protein hCtr1 is transcriptionally regulated by specificity protein 1 (Sp1) in response to the cellular copper level. However, it is not known how Sp1, a zinc-finger-protein (ZFP), can sense copper ions in cells. Here we found that Sp1 demonstrates high binding affinity to cuprous ions, even stronger than Cu-Atox1 binding. Cu(i) can displace Zn(ii) in Sp1, resulting in a well-folded 'Copper-Finger-Protein' (CFP). Although only very little structural alteration occurs upon copper binding, CFP cannot recognize the promoter of hCtr1, therefore copper binding interrupts the transcription. This result indicates that, in addition to apo-to-holo alteration, metal substitution can also lead to transcriptional switch in metal sensing. This work provides insight into the copper sensing mechanism of Sp1 at the molecular level.

Binding States of Protein-Metal Complexes in Cells

The identification of endogenous proteins as well as their binding to metal ions in living cells is determined by combining pulsed electrophoretic separations with nanoelectrospray ionization followed by mass spectrometric detection. This approach avoids problems resulting from the complicated cellular environment. In this manner, we demonstrate the rapid identification (300 ms or less) of intact proteins from living E. coli cells including the complexation of calmodulin with calcium ion. The latter showed different binding states from those observed in in vitro studies. These observations also reveal in vitro measurements do not necessarily represent the actual situation in living cells. We conclude that the attempted in situ measurement of intracellular proteins with minimal sampling processes should be preferred.

Kinetics and thermodynamics of zinc(II) and arsenic(III) binding to XPA and PARP-1 zinc finger peptides

Inhibition of DNA repair is an established mechanism of arsenic co-carcinogenesis, and may be perpetuated by the binding of As(III) to key zinc finger (zf) DNA repair proteins. Validated molecular targets of As(III) include the first zinc finger domain of Poly (ADP-Ribose) Polymerase 1 (PARP-1), and the zinc finger domain of Xeroderma Pigmentosum Complementation Group A (XPA). In order to gain an understanding of the thermodynamic and kinetic parameters of the interaction of As(III) with these two zinc finger motifs, a fluorescence based approach was used to investigate Zn(II) and As(III) binding to synthetic model peptides corresponding to the zf motif of XPA and first zf motif of PARP-1, referred to in this paper as XPAzf and PARP-1zf-1, respectively. While XPAzf and PARP-1zf-1 display similar relative affinities for As(III), PARP-1zf-1 shows a potential kinetic advantage over XPAzf for As(III) binding, with a rate constant for the fast phase of formation of As(III)-PARP-1zf-1 approximately 4-fold higher than for As(III)-XPAzf. However, the binding of Zn(II) with either peptide proceeds at a faster rate than As(III). Notably, XPAzf demonstrates comparable affinities for binding both metals, while PARP-1zf-1 shows a slightly higher affinity for Zn(II), suggesting that the relative concentrations of Zn(II) and As(III) in a system may significantly influence which species predominates in zinc finger occupancy. These results provide insight into the mechanisms underlying interactions between zinc finger structures and As(III), and highlight the potential utility of zinc supplementation in mitigating adverse effects of As(III) on zinc finger functions in vivo.

Glutathione selectively modulates the binding of platinum drugs to human copper chaperone Cox17

The copper chaperone Cox17 (cytochrome c oxidase copper chaperone) has been shown to facilitate the delivery of cisplatin to mitochondria, which contributes to the overall cytotoxicity of the drug [Zhao et al. (2014) Chem. Commun. 50: , 2667-2669]. Kinetic data indicate that Cox17 has reactivity similar to glutathione (GSH), the most abundant thiol-rich molecule in the cytoplasm. In the present study, we found that GSH significantly modulates the reaction of platinum complexes with Cox17. GSH enhances the reactivity of three anti-cancer drugs (cisplatin, carboplatin and oxaliplatin) to Cox17, but suppresses the reaction of transplatin. Surprisingly, the pre-formed cisplatin-GSH adducts are highly reactive to Cox17; over 90% platinum transfers from GSH to Cox17. On the other hand, transplatin-GSH adducts are inert to Cox17. These different effects are consistent with the drug activity of these platinum complexes. In addition, GSH attenuates the protein aggregation of Cox17 induced by platination. These results indicate that the platinum-protein interactions could be substantially influenced by the cellular environment.