Arsenate reductases

Bennett MS, Z Guan, M Laurberg, X-D Su (2001) Bacillus subtilis arsenate reductase is structurally and functionally similar to low molecular weight protein tyrosine phosphatases. Proc Natl Acad Sci USA 98 13577-13582. 

Krafft T, JM Macey (1998) Purification and characterization of the respiratory arsenate reductase of Chrysio-genes arsenatis. Eur J Biochem 255 647-653. 

Liu J, TB Gladysheva, L Lee, BP Rosen (1995) Identification of an essential cysteinyl residue in the ArsC arsenate reductase plasmid R 773. Biochemistry 34 13472-13476. 

Saltikov CW, DK Newman (2003) Genetic identification of a respiratory arsenate reductase. Proc Natl Acad Sci USA 100 10983-10988. 

The chlorate reductase has been characterized in strain GR-1 where it was found in the periplasm, is oxygen-sensitive, and contains molybdenum, and both [3Fe-4S] and [4Fe-4S] clusters (Kengen et al. 1999). The arsenate reductase from Chrysiogenes arsenatis contains Mo, Fe, and acid-labile S (Krafft and Macy 1998), and the reductase from Thauera selenatis that is specific for selenate, is located in the periplasmic space, and contains Mo, Fe, acid-labile S, and cytochrome b (Schroeder et al. 1997). In contrast, the membrane-bound selenate reductase from Enterobacter cloacae SLDla-1 that cannot function as an electron acceptor under anaerobic conditions contains Mo and Fe and is distinct from nitrate reductase (Ridley et al. 2006). 

Arsenate reductase (and y-glutamylcysteine synthetase) Increased for arsenate, Cd Increased for arsenic, Cd ... 

Dhankher, O. P., Sashti, N. A., Rosen, B. P., Fuhrmarm, M., and Meagher, R. B., 2003, Increased cadmium tolerance and accumulation by plants expressing bacterial arsenate reductase, New Phytol. 159 431-441. 

Arsenate Arsenate reductase C. arsenatis Kraft and Macy (1998)... 

Chrysiogenes arsenatis is the only known organism capable of using acetate as the electron donor and arsenate as the terminal electron acceptor for growth. This reduction of arsenate to arsenite is catalyzed by an inducible respiratory arsenate reductase, which has been isolated and characterized by Kraft and Macy (1998). Arsenate reductase (Arr) from C. arsenatis is a... 

A second example of a membrane-bound arsenate reductase was isolated from Sulfurospirillum barnesii and was determined to be a aiPiyi-heterotrimic enzyme complex (Newman et al. 1998). The enzyme has a composite molecular mass of 100kDa, and a-, P-, and y-subunits have masses of 65, 31, and 22, respectively. This enzyme couples the reduction of As(V) to As(III) by oxidation of methyl viologen, with an apparent Kra of 0.2 mM. Preliminary compositional analysis suggests that iron-sulfur and molybdenum prosthetic groups are present. Associated with the membrane of S. barnesii is a h-type cytochrome, and the arsenate reductase is proposed to be linked to the electron-transport system of the plasma membrane. 

The recently isolated Desulfotomaculum strain Ben-RB is able to grow using lactate as a substrate and arsenate as the sole electron acceptor (Macy et al. 2000). It has been proposed that arsenate reductase is associated with the respiratory chain of this organism, because >98% of the arsenate reductase bound to the plasma membrane. 

Gregus, Z. and Nemeti, B. (2002) Purine nucleoside phosphorylase as a cytosolic arsenate reductase. Toxicological Sciences, 70(1), 13-19. 

Dhankher, O.P., McKinney, E.C., Barry P. Rosen, and Meagher, R.B. 2006. Hyperaccumulation of arsenic in the shoots of Arabidopsis silenced for arsenate reductase, ACR2. Proceedings of the National Academy of Sciences USA, 103 5413-18. 

Ellis, D.R., Gumaelius, L., Indriolo, E., Pickering, I.J., Banks, J.A., and Salt, D.E. 2006. A novel arsenate reductase from the arsenic hyperaccumulating fern Pteris vittata. Plant Physiology, 141 1544-54. 

Radabaugh, T.R., Aposhian, H.V. (2000). Enzymatic reduction of arsenic compounds in mammalian systems reduction of arsenate to arsenite by human liver arsenate reductase. Chem. Res. Toxicol. 13 26-30. 

Recently, the respiratory arsenate reductase was characterized from Shewanella sp. strain ANA-3 (Malasam et al, 2008), which was initially identified in the same strain... 

FIGURE 72.2. Arsenic detoxification mechanisms (reduction, oxidation, methylation, and resistance) in prokaryotes. (A) Respiratory arsenate reductase (Arr) is involved in the reduction of As(V) by the dissimilatory arsenate respiring organisms. (B) Arsenite oxidase (Aox/Aso) is responsible for oxidation of As(III) by chemoautotrophic or heterotrophic arsenite oxidizers. 

FIGURE 72.3. Molecular organization of arrAB (periplasmic arsenate reductase) and arsDABC (cytoplasmic arsenate reductase) of Shewanella strain ANA-3 (from GenBank Accession no. AY271310). arrAB gene cluster is located upstream in the opposite orientation to an arsDABC. aa-amino acid (modified Ifom Saltikov and Newman, 2003 Silver and Phung, 2005). 

Alcaligenes faecalis and five members of the p Proteobacteria are heterotrophic arsenite oxidizers, whereas Pseudomonas arsenitoxidans and NT-26 grew anaerobically through chemoautotrophic oxidation (Oremland and Stolz, 2005 Santini et al, 2000). However, six members of a Proteobacteria (Ben-5, NT-3, NT-4, NT-2, NT-26, and NT-25) and one member of y Proteobacteria (MLHE-1) were known chemohthoautotrophic arsenite oxidizers (Oremland et al, 2002). The best characterized and probably most studied of aU arsenite oxidizers is Alcaligenes faecalis, a heterotrophic arsenite oxidizer (Osborne and Enrlich, 1976). The arsenite oxidase from Alcaligenes faecalis has been purified and structurally characterized (Ellis et al, 2001). A similar enzyme has also been purified from the heterotrophic arsenite oxidizers Hydrogenophaga sp. strain NT-14 (Vanden Hoven and Santini, 2004) and the chemolithoautotrophic Rhizobium sp. strain NT-26 (Santini and Vanden Hoven, 2004), which indicate that the arsenite oxidase enzyme is also a member of the DMSO reductase family of molybdenum enzymes, similar to the respiratory arsenate reductases (Arr). The arsenite oxidase heterodimer comprises an 88 kDa catalytic subunit encoded by the aoxB gene that contains a [3Fe-4S] cluster and molybdenum bound to the pyranopterin cofactor and a 14 kDa subunit... 

The enzymology of arsenic biomethylation is complicated because of its many oxidation states, its propensity to react with sulfur compounds, and low concentrations of arsenic compounds in biological specimens. The chemical intermediates and reactions in the metabolism of arsenate are similar in microorganisms and animals. However, in microorganisms, the reactions tend to proceed to methylarsines, whereas in mammalian species the major urinary metabolite is generally dimethylarsinate and only a very small amount of it is reduced further. The arsenate reductase and methylarsonate reductase were thought to play an important role in arsenic biomethylation however, with the exception of arsenate reductase most of the enzymatic experiments involved mammalian systems. 

Arsenate reductase can reduce arsenate to arsenite, and is involved in bacterial resistance to arsenic however, the reduction can also be mediated nonezymatically by reduced glutathione. The arsenate reductase utilizes thioredoxin and glutaredoxin rather than glutathione which is usually postulated to play a role in biomethylation. The cytosolic and periplasmic, two different arsenate reductases, exist in microorganisms encoded by ars and arr systems. Escherichia... 

The structure of the bacterial ArsC from Escherichia coli plasmid R773 has been solved at 1.65 A resolution, and revealed that arsenate reductase (ArsC) has only one cysteine residue (Cys-12) in the active site, surrounded by an arginine triad composed of Arg-60, Arg-94, and Arg-107 (Mukhopadhyay et al, 2002). However, the arsenate reductase from Staphylococcus aureus has three cysteine residues (Cys-10, Cys-82, and Cys-89). The biochemical and mutational studies established that the arsenate binds to the triad of arginine (Arg-60, Arg-94, and Arg-107) residues and forms a covalent bond with the cysteine (Cys-12) residue near the N-terminus at the active site of arsenate reductase and/or participates in catalysis (Rosen, 2002a Silver and Phung, 2005 Shi etal, 2003 Martin et al, 2001). 

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