Binding of Arsenic by Common Functional Groups: An Experimental and Quantum-Mechanical Study (original) (raw)
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The biological effects of arsenic are diverse and the mechanisms of arsenic toxicity and carcinogenicity are complicated. Arsenic−sulfur interactions are the chemical basis of most of these effects. Trivalent arsenicals bind to thiols that are contained in numerous intracellular and cell-surface proteins, and this arsenic−protein binding often triggers cellular responses. For example, arsenic binding to PML or some mitochondrial proteins is a key step leading to cell differentiation or apoptosis induced by As2O3. A low baseline cellular glutathione content and a high expression level of the primary membrane transporter aquaglyceroporin 9 that mediates uptake of As2O3 into cells predetermine the selectivity of APL toward As2O3.407 Generation of cellular ROS is often implicated in the inhibition of various enzymes by arsenic; however, it cannot supplant the role of direct protein binding by trivalent arsenicals. ROS generation itself may result from thiol chelation or complexation in dithiol-containing enzymes, such as pyruvate dehydrogenase (PDH), by trivalent arsenic metabolites.
Speciation, metabolism, toxicity, and protein-binding of different arsenic species in human cells
2014
I would like to thank my advisor, Dr Yong Cai for his guidance, continuous support, and patience throughout my PhD studies. I am very grateful for all the scientific discussions and guidance I have received from Guangliang Liu, PhD. I would also like to thank him for the countless hours he patiently helped me to figure out and fix the problems I had with the analytical instrumentation.
Therapeutic and analytical applications of arsenic binding to proteins
Metallomics : integrated biometal science, 2015
Arsenic binding to proteins plays a pivotal role in the health effects of arsenic. Further knowledge of arsenic binding to proteins will advance the development of bioanalytical techniques and therapeutic drugs. This review summarizes recent work on arsenic-based drugs, imaging of cellular events, capture and purification of arsenic-binding proteins, and biosensing of arsenic. Binding of arsenic to the promyelocytic leukemia fusion oncoprotein (PML-RARα) is a plausible mode of action leading to the successful treatment of acute promyelocytic leukemia (APL). Identification of other oncoproteins critical to other cancers and the development of various arsenicals and targeted delivery systems are promising approaches to the treatment of other types of cancers. Techniques for capture, purification, and identification of arsenic-binding proteins make use of specific binding between trivalent arsenicals and the thiols in proteins. Biarsenical probes, such as FlAsH-EDT2 and ReAsH-EDT2, cou...
Arsenic(III) Species Inhibit Oxidative Protein Folding in Vitro †
Biochemistry, 2009
The success of arsenic trioxide in the treatment of acute promyelocytic leukemia has renewed interest in the cellular targets of As(III) species. The effects of arsenicals are usually attributed to their ability to bind vicinal thiols or thiol-selenols in pre-folded proteins thereby compromising cellular function. The present studies suggest an additional, more pleiotropic, contribution to the biological effects of arsenicals. As(III) species, by avid coordination to the cysteine residues of unfolded reduced proteins, can compromise protein folding pathways. Three representative As(III) compounds (arsenite; monomethylarsenous acid, MMA; and an aryl arsenical, PSAO) have been tested with three reduced secreted proteins (lysozyme, ribonuclease A and riboflavin binding protein, RfBP). Using absorbance, fluorescence and pre-steady state methods, we show that arsenicals bind tightly to low micromolar concentrations of these unfolded proteins with stoichiometries of 1 As(III) per 2 thiols for MMA and PSAO and 1 As(III) for every 3 thiols with arsenite. Arsenicals, at 10 μM, strongly disrupt the oxidative folding of RfBP even in the presence of 5 mM reduced glutathione, a competing ligand for As(III) species. MMA catalyzes the formation of amyloid-like monodisperse fibrils using reduced RNase. These in vitro data show that As(III) species can slow, or even derail, protein folding pathways. In vivo, the propensity of As(III) species to bind to unfolded cysteine-containing proteins may contribute to oxidative and protein folding stresses that are prominent features of the cellular response to arsenic exposure.
Methylated Trivalent Arsenic-Glutathione Complexes are More Stable than their Arsenite Analog
Bioinorganic Chemistry and Applications, 2008
The trivalent arsenic glutathione complexes arsenic triglutathione, methylarsonous diglutathione, and dimethylarsinous glutathione are key intermediates in the mammalian metabolism of arsenite and possibly represent the arsenic species that are transported from the liver to the kidney for urinary excretion. Despite this, the comparative stability of the arsenic-sulfur bonds in these complexes has not been investigated under physiological conditions resembling hepatocyte cytosol. Using size-exclusion chromatography and a glutathione-containing phosphate buffered saline mobile phase (5 or 10 mM glutathione, pH 7.4) in conjunction with an arsenic-specific detector, we chromatographed arsenite, monomethylarsonous acid, and dimethylarsinous acid. The on-column formation of the corresponding arsenic-glutathione complexes between 4 and 37 • C revealed that methylated arsenic-glutathione complexes are more stable than arsenic triglutathione. The relevance of these results with regard to the metabolic fate of arsenite in mammals is discussed.
Arsenic is a type 1 carcinogen and its toxicity is critically dependent on chemical speciation. However, after decades of research, the biogenesis of at least fifty naturally occurring arsenic species is still not well understood. Here, based on experimental work, it is proposed a set of pathways for the formation of multiple arsenic species that might help to clarify the present situation. These are focused on the thiol protein arsenic bond and on its interaction with reactive metabolites. In fact, arsenic bound to glutathione interacting with sulfur adenosyl methionine (SAM), MethylCB12 and AdoCB12, forms a number of complexes that might be key intermediates in arsenic biochemistry. These include dimethylarsino glutathione (DMAG) m/z 412 [M+H] +, synthesized non-enzymatically from glutathione and cacodylate. Trimethylarsonio glutathione (TMAG) m/z 426 [M] + synthesized from DMA, GSH and SAM, apparently by a classical Challenger methylcarbonium attack. Tetramethyl arsonium ion m/z 135 [M] + is formed in a third step, apparently by carbanion methylation. The presence of trimethylarsine oxide (TMAO) m/z 137 [M+H] + is attributed to the hydrolysis of TMAG or TMA, or to carbanion methylation of dimethylarsinoyl glutathione (m/z 428 [M] +) formed from cacodylate and GSH. Cantoni type attacks of DMAG on SAM were unsuccessful, eventually due to competition of the trivalent S+ atom of SAM for the AsIII atom attack. The presence of dimethylarsonio diglutathione (DMADG m/z 717 [M] +), is suggested to result from a GS- attack on dimethylarsenoyl glutathione (m/z 428 [M+H] +). The presence of dimethylarsenoyladenosine (m/z 372 [M+H] +), trimethylarsenosugar adenine (m/z 370 [M] +), and dimethylthioarsenosugar adenine (m/z 388 [M+H] +), is explained by the synthesis of the pecursor dimethylarsonioadenosine glutathione DMAAG (m/z 661 [M] +), a likely source of oxo-and trimethylated arsenosugars, as well as of thio-arsenosugars by the cleavage of its SC bond. The results gathered suggest that cell vacuoles might play a major role in arsenic metabolism, and that the dominance of oxo-As sugars, in algae extracts, may be supported by a mechanism of synthesis independent of DMAAG (m/z 661). They also offer an explanation for the reason why arsenobetaine, and tetramethylarsonium are loosely bound to biotic tissues. Four arsenic species new to science, to the best of our knowledge, and a number of known arsenic compounds were synthesized in this work, identified by HPLC-ESI-MSn and FTICR-ESI-MS, andsuggestions regarding their mechanisms of synthesis were advanced. These resultsprovide a framework for arsenic biochemistry which may explain the origin of a significant part of arsenic known metabolites.
Arsenic Toxicity: Molecular Targets and Therapeutic Agents
Biomolecules, 2020
High arsenic (As) levels in food and drinking water, or under some occupational conditions, can precipitate chronic toxicity and in some cases cancer. Millions of people are exposed to unacceptable amounts of As through drinking water and food. Highly exposed individuals may develop acute, subacute, or chronic signs of poisoning, characterized by skin lesions, cardiovascular symptoms, and in some cases, multi-organ failure. Inorganic arsenite(III) and organic arsenicals with the general formula R-As2+ are bound tightly to thiol groups, particularly to vicinal dithiols such as dihydrolipoic acid (DHLA), which together with some seleno-enzymes constitute vulnerable targets for the toxic action of As. In addition, R-As2+-compounds have even higher affinity to selenol groups, e.g., in thioredoxin reductase that also possesses a thiol group vicinal to the selenol. Inhibition of this and other ROS scavenging seleno-enzymes explain the oxidative stress associated with arsenic poisoning. Th...
Identification of arsenic-binding proteins in human breast cancer cells
Cancer Letters, 2007
Exposure to high levels of arsenic can cause a wide range of health effects, including cancers of the bladder, lung, skin, and kidney. However, the mechanism(s) of action underlying these deleterious effects of arsenic remains unclear. Arsenic binding to cellular proteins is a possible mechanism of toxicity, and identifying such binding is analytically challenging because of the large concentration range and variety of proteins. We describe here an affinity selection technique, coupled with mass spectrometry, to select and identify specific arsenic-binding proteins from a large pool of cellular proteins. Controlled experiments using proteins either containing free cysteine(s) or having cysteine blocked showed that the arsenic affinity column specifically captured the proteins containing free cysteine(s) available to bind to arsenic. The technique was able to capture and identify trace amounts of bovine biliverdin reductase B present as a minor impurity in the commercial preparation of carbonic anhydrase II, demonstrating the ability to identify arsenic-binding proteins in the presence of a large excess of non-specific proteins. Application of the technique to the analysis of subcellular fractions of A549 human lung carcinoma cells identified 50 proteins in the nuclear fraction, and 24 proteins in the membrane/organelle fraction that could bind to arsenic, adding to the current list of only a few known arsenic-binding proteins.
Arsenic binding proteins from human lymphoblastoid cells
Toxicology Letters, 1999
Arsenic is a ubiquitous contaminant of drinking water and food. The mechanisms of the toxic action of inorganic arsenic are unknown. We report the isolation of proteins having a high affinity for arsenic in the + 3 oxidation state that are induced by arsenite (AsIII) in human lymphoblastoid cells. The arsenic-binding proteins were isolated using a p-aminophenylarsine oxide affinity column. At least four proteins of 50, 42, 38.5 and 19.5 kDa were isolated by elution with 10 or 100 mM 2-mercaptoethanol. Two proteins were tentatively identified as tubulin and actin on the basis of their molecular weights and previously reported affinity for the arsenic column. The identities of the remaining proteins are unknown. Heme oxygenase 1 was induced by AsIII but did not bind to the arsenic affinity column. We conclude that AsIII induces multiple proteins that have variable affinities for arsenic in the + 3 state as judged by the concentration of 2-mercaptoethanol required for their elution. The arsenic binding motif of these proteins may involve three thiol groups arranged 3-6 Å apart by the tertiary structure of the protein as suggested by others. These proteins may serve as high affinity binding sites for AsIII and may be involved in the biological action of AsIII.