Pb(II)-translocating P-type ATPases

Abstract

The cad operon of Staphylococcus aureus plasmid pI258, which confers cadmium resistance, encodes a transcriptional regulator, CadC, and CadA, an ATP-coupled Cd(II) pump that is a member of the superfamily of cation-translocating P-type ATPases. The Escherichia coli homologue of CadA, termed ZntA, is a Zn(II)/Cd(II) pump. The results described in this paper support the hypothesis that ZntA and CadA are Pb(II) pumps. First, CadC is a metal-responsive repressor that responds to soft metals in the order Pb>Cd>Zn. Second, both CadA and ZntA confer resistance to Pb(II). Third, transport of 65 Zn(II) in everted membrane vesicles of E. coli catalyzed by either of these two P-type ATPase superfamily members is inhibited by Pb(II).Exposure to environmental sources of lead is a serious public health concern. In humans chronic lead exposure produces neurotoxicity, anemia, and kidney damage, and acute lead toxicity can be fatal. Neither the specific lead transporters nor the regulatory elements that control the expression of the transporter genes have been identified. As models for human metal toxicity, we have been characterizing transporters for toxic metals and their genetic regulation (1, 2) and report here the identification of two P-type ATPases that are responsible for Pb(II) extrusion and resistance in bacteria.Bacterial metal ion resistance probably arose early in evolution due to widespread geological occurrence of metals. Bacterial cells have chromosomally and plasmid-encoded mechanisms for extrusion of antimicrobial substances, including toxic soft metals (3). While the ionic forms of some of these metals such as zinc and copper are essential for all organisms, all of these ions are toxic in excess. ZntA from Escherichia coli and CadA from plasmid pI258 of Staphylococcus aureus are both members of the superfamily of P-type cation-translocating ATPases but belong to a subgroup of soft metal transporters that includes CopA, a Cu(I) pump from Enterococcus hirae, and eukaryotic Cu(I) homeostasis proteins such as the Menkes and Wilson disease-associated proteins (1, 4, 5). ZntA has been shown to catalyze ATP-dependent transport of Zn(II) and Cd(II) (6), and CadA has been shown to transport Cd(II) (7). Both have been shown to confer resistance to cadmium and zinc ions (8 -10). The pI258 cadCA operon is regulated at the transcriptional level by the product of the cadC gene, which encodes the 122-residue CadC repressor (11-13).In this report, we show that CadC repression of the cad promoter is relieved upon addition of soft metals, with the order of effectiveness Pb(II) Ͼ Cd(II) Ͼ Zn(II). In E. coli Zn(II) responsiveness could be observed only in a zntA-disrupted strain. The zntA-disrupted strain of E. coli exhibited hypersensitivity to Pb(II) that was complemented by cadA, indicating that both soft metal-translocating P-type ATPases are essential for Pb(II) resistance in bacteria. Everted membrane vesicles from cells expressing either zntA or cadA exhibited ATPdependent 65 Zn(II) accumulation. Since no radioisotopes of ...

Improving the sensitivity of bacterial bioreporters for heavy metals

“…The existence of a Zn-specific sensor element is peculiar, as all of the transcription factors and resistance mechanisms known for Zn 2+ thus far cross-react with Cd 2+ and Pb 2+ (see Table 1). 17,[21][22][23][24] However, as only three sensor elements (the promoters of zntA from E. coli, cadA from P. putida and cadA from S. aureus) have been previously used for the construction of Zn/Cd/Pb-bioreporters, it is still possible that an open-minded search for new heavy-metal-regulated promoters would yield bioreporters with different specificities.…”

Plasmid profile and curing analysis of Pseudomonas aeruginosa as metal resistant

“…Lead is a hazardous waste and is highly toxic to humans, plants and animals (Low et al, 2000). In humans chronic lead exposure produces neurotoxicity, anaemia and kidney damage and acute lead toxicity can be fatal (Rensing et al, 1998). Similarly chromium (VI) is the toxic form of chromium released during many industrial processes, including electroplating, leather tanning and pigment manufacture (Prasenjit and Sumathi, 2005).…”

Organic acids enhance the uptake of lead by wheat roots

“…Lead substitutes for calcium in the activation of calmodulin-dependent phosphodiesterase. CadA and ZntA have been discovered as two Pb(II)-translocating P-type ATPase (Rensing et al 1998). Still largely unanswered in the question how lead is taken up into plant cells under the influence of organic acids, and what the exact speciation of lead is within plant cells.…”