As(III) and Sb(III) Uptake by GlpF and Efflux by ArsB in Escherichia coli

Meng, Yuling; Liu, Zijuan; Rosen, Barry P.

doi:10.1074/jbc.m400037200

Cited by 260 publications

(186 citation statements)

References 23 publications

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“…However, in paddy soils, which are flooded during much of the rice growing season, arsenite becomes the predominant chemical species of As (14). It has been shown that arsenite is taken up via aquaglyceroporins in microbes (13,(15)(16)(17). Evidence from physiological studies suggests that arsenite may also be transported by aquaporins in rice (18), although the exact mechanism of arsenite uptake has not been identified in higher plants.…”

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confidence: 99%

Transporters of arsenite in rice and their role in arsenic accumulation in rice grain

Feng

Yamaji

Mitani

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

1,232

861

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Arsenic poisoning affects millions of people worldwide. Human arsenic intake from rice consumption can be substantial because rice is particularly efficient in assimilating arsenic from paddy soils, although the mechanism has not been elucidated. Here we report that two different types of transporters mediate transport of arsenite, the predominant form of arsenic in paddy soil, from the external medium to the xylem. Transporters belonging to the NIP subfamily of aquaporins in rice are permeable to arsenite but not to arsenate. Mutation in OsNIP2;1 (Lsi1, a silicon influx transporter) significantly decreases arsenite uptake. Furthermore, in the rice mutants defective in the silicon efflux transporter Lsi2, arsenite transport to the xylem and accumulation in shoots and grain decreased greatly. Mutation in Lsi2 had a much greater impact on arsenic accumulation in shoots and grain in field-grown rice than Lsi1. Arsenite transport in rice roots therefore shares the same highly efficient pathway as silicon, which explains why rice is efficient in arsenic accumulation. Our results provide insight into the uptake mechanism of arsenite in rice and strategies for reducing arsenic accumulation in grain for enhanced food safety.efflux ͉ influx ͉ arsenic contamination ͉ silicon ͉ aquaporin A rsenic (As) is a human carcinogen, and there may be no threshold below which it does not cause cancer (1). More than 40 million people worldwide are at risk from drinking As-contaminated groundwater (2), and chronic inorganic As poisoning has reached a massive scale in Bangladesh and West Bengal, India (3). In these countries, As-contaminated groundwater is also widely used for irrigating crops during dry season rice production, adding Ͼ1,000 metric tons of As to soil per year in Bangladesh alone and resulting in As accumulation in soils and elevated As uptake by crops (4-6). Elevated As accumulation in rice has the potential to become a new disaster for the population in Southeast Asia (7). As concentrations in rice grain are often high enough to cause concern even in uncontaminated soils containing background levels of As, because paddy rice appears to be particularly efficient in As assimilation compared with other cereal crops (8). Worldwide market surveys show that rice grain contains considerably higher levels of inorganic As than other foods (9, 10). Human intake of As from consumption of rice can be substantial, especially for people who consume a lot of rice (11). It is therefore crucial that the mechanism of As accumulation in rice is understood to counteract this widespread contamination of the food chain.Plants take up arsenate, the predominant form of As in aerobic soils, through phosphate transporters (12, 13). However, in paddy soils, which are flooded during much of the rice growing season, arsenite becomes the predominant chemical species of As (14). It has been shown that arsenite is taken up via aquaglyceroporins in microbes (13,(15)(16)(17). Evidence from physiological studies suggests that arsenite may also be transp...

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mentioning

confidence: 99%

Transporters of arsenite in rice and their role in arsenic accumulation in rice grain

Feng

Yamaji

Mitani

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

1,232

861

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“…It transports As(III) but has higher affinity for Sb(III). ArsB is an antiporter that catalyzes the exchange of trivalent metalloid for protons, coupling arsenite efflux to the electrochemical proton gradient (9).…”

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Properties of Arsenite Efflux Permeases (Acr3) from Alkaliphilus metalliredigens and Corynebacterium glutamicum

Meng

Ordóñez

et al. 2009

Journal of Biological Chemistry

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Members of the Acr3 family of arsenite permeases confer resistance to trivalent arsenic by extrusion from cells, with members in every phylogenetic domain. In this study bacterial Acr3 homologues from Alkaliphilus metalliredigens and Corynebacterium glutamicum were cloned and expressed in Escherichia coli. Modification of a single cysteine residue that is conserved in all analyzed Acr3 homologues resulted in loss of transport activity, indicating that it plays a role in Acr3 function. The results of treatment with thiol reagents suggested that the conserved cysteine is located in a hydrophobic region of the permease. A scanning cysteine accessibility method was used to show that Acr3 has 10 transmembrane segments, and the conserved cysteine would be predicted to be in the fourth transmembrane segment.

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“…The ArsA subunit is an As(III)/Sb(III)-stimulated ATPase (21), and the ArsB subunit is an antiporter that catalyzes As(III)/H ϩ exchange (22). The 583-residue ArsA ATPase is composed of two homologous A1 and A2 halves that are connected by a short linker (3).…”

Section: Discussionmentioning

confidence: 99%

Nonequivalence of the Nucleotide Binding Domains of the ArsA ATPase

Jiang

Bhattacharjee

Zhou

et al. 2005

Journal of Biological Chemistry

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The arsRDABC operon of Escherichia coli plasmid R773 encodes the ArsAB pump that catalyzes extrusion of the metalloids As(III) and Sb(III), conferring metalloid resistance. The catalytic subunit, ArsA, is an ATPase with two homologous halves, A1 and A2, connected by a short linker. Each half contains a nucleotide binding domain. The overall rate of ATP hydrolysis is slow in the absence of metalloid and is accelerated by metalloid binding. The results of photolabeling of ArsA with the ATP analogue 8-azidoadenosine 5-[␣-32 P]-triphosphate at 4°C indicate that metalloid stimulation correlates with a >10-fold increase in affinity for nucleotide. To investigate the relative contributions of the two nucleotide binding domains to catalysis, a thrombin site was introduced in the linker. This allowed discrimination between incorporation of labeled nucleotides into the two halves of ArsA. The results indicate that both the A1 and A2 nucleotide binding domains bind and hydrolyze trinucleotide, even in the absence of metalloid. Sb(III) increases the affinity of the A1 nucleotide binding domain to a greater extent than the A2 nucleotide binding domain. The ATP analogue labeled with 32 P at the ␥ position was used to measure hydrolysis of trinucleotide at 37°C. Under these catalytic conditions, both nucleotide binding domains hydrolyze ATP, but hydrolysis in A1 is stimulated to a greater degree by Sb(III) than A2. These results suggest that the two homologous halves of the ArsA may be functionally nonequivalent.In Escherichia coli the ArsAB pump encoded by the ars operon of plasmid R773 confers resistance to arsenicals and antimonials (1). ArsA is the catalytic subunit of the pump that hydrolyzes ATP in the presence of the trivalent forms of the two metalloids. ATP hydrolysis is coupled to extrusion of As(III) or Sb(III) through ArsB, which serves both as a membrane anchor for ArsA and as the substrate-conducting pathway. Upon overexpression, ArsA exists primarily as a soluble protein in the cytosol. Soluble ArsA has been purified and characterized and has been shown to be an As(III)/Sb(III)-stimulated ATPase (2).ArsA is composed of homologous N-terminal (A1) and Cterminal (A2) halves that are connected by a short linker (3). Each contains a nucleotide binding domain (NBD) 1 (4) (Fig. 1), and both NBDs are required for ATPase activity and metalloid transport (5, 6). A novel metalloid binding domain located at the A1-A2 interface diametrically opposite to the NBDs modulates ATPase activity (4,7,8). Two stretches of residues, D 142 TAPTGH 148 in A1 and D 447 TAPTGH 453 in A2, physically connect the metalloid binding domain to the A1 and A2 NBDs, respectively. The metalloid binding domain is composed of three metalloid atoms, each of which is coordinated by two protein ligands, one of which is donated by A1 and the other by A2. Thus the metalloid atoms serve as the "molecular glue" that brings the two halves of the protein together, activating catalysis. The basal rate of catalysis has been thought to reflect the activity of onl...

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As(III) and Sb(III) Uptake by GlpF and Efflux by ArsB in Escherichia coli

Cited by 260 publications

References 23 publications

Transporters of arsenite in rice and their role in arsenic accumulation in rice grain

Transporters of arsenite in rice and their role in arsenic accumulation in rice grain

Properties of Arsenite Efflux Permeases (Acr3) from Alkaliphilus metalliredigens and Corynebacterium glutamicum

Nonequivalence of the Nucleotide Binding Domains of the ArsA ATPase

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