Molybdate and Tungstate: Uptake, Homeostasis, Cofactors, and Enzymes

Schwarz, Guenter; Hagedoorn, Peter‐Leon; Fischer, Katrin

doi:10.1007/7171_2006_088

Cited by 22 publications

(33 citation statements)

References 117 publications

(107 reference statements)

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“…They do in E. coli, and ABC uptake systems are needed for this. Examples are ZnuACB for zinc (44), NikABC for nickel (33), and ModABCD for molybdate (46,52). ZnuABC, ZntA, and their regulators Zur and ZntR form a shunt as described above, controlling the cytoplasmic zinc content in the bacterium (43).…”

Section: Discussionmentioning

confidence: 99%

Contributions of Five Secondary Metal Uptake Systems to Metal Homeostasis of Cupriavidus metallidurans CH34

et al. 2011

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Cupriavidus metallidurans is adapted to high concentrations of transition metal cations and is a model system for studying metal homeostasis in difficult environments. The elemental composition of C. metallidurans cells cultivated under various conditions was determined, revealing the ability of the bacterium to shield homeostasis of one essential metal from the toxic action of another. The contribution of metal uptake systems to this ability was studied. C. metallidurans contains three CorA members of the metal inorganic transport (MIT) protein family of putative magnesium uptake systems, ZupT of the ZRT/IRT protein, or ZIP, family, and PitA, which imports metal phosphate complexes. Expression of the genes for all these transporters was regulated by zinc availability, as shown by reporter gene fusions. While expression of zupT was upregulated under conditions of zinc starvation, expression of the other genes was downregulated at high zinc concentrations. Only corA 1 expression was influenced by magnesium starvation. Deletion mutants were constructed to characterize the contribution of each system to transition metal import. This identified ZupT as the main zinc uptake system under conditions of low zinc availability, CorA 1 as the main secondary magnesium uptake system, and CorA 2 and CorA 3 as backup systems for metal cation import. PitA may function as a cation-phosphate uptake system, the main supplier of divalent metal cations and phosphate in phosphate-rich environments. Thus, metal homeostasis in C. metallidurans is achieved by highly redundant metal uptake systems, which have only minimal cation selectivity and are in combination with efflux systems that "worry later" about surplus cations.Sophisticated cellular biochemistry needs metals as cofactors. About 40% of all enzymes have them, ranking from Mg (16%) Ͼ Zn (9%) Ͼ Fe (8%) Ͼ Mn (6%) Ͼ Ca (2%) Ͼ Co and Cu (1%) down to K, Na, Ni, V, Mo, W, and only one example of Cd (59). It is an interesting question how the correct metal is allocated to the right protein, a challenge especially for the divalent metal cations Mg 2ϩ , Zn 2ϩ , Fe 2ϩ , Mn 2ϩ , Co 2ϩ , Ni 2ϩ , and Cu 2ϩ . These metals compete with each other for the metal binding sites in enzymes (16). Additionally, Fe 2ϩ/3ϩ and Cu ϩ/2ϩ promote dangerous reactive oxygen species in Fenton and Fenton-like reactions, as described by Haber and Weiss (13).Part of the solution to this problem might be to keep the metal cation bouquet in any cellular compartment in a way that minimizes competition for metal binding sites and the Fenton reaction. This leads to the question of how the cellular metal cation bouquet can be maintained in environments that may contain a single metal in a concentration range from pM to mM. The betaproteobacterium Cupriavidus metallidurans strain CH34 is able to keep its metal homeostasis under a variety of such adverse conditions (19,28,30). The organism can be found in many mesophilic metal-contaminated environments around the globe, such as zinc deserts of Belgium (8). Key to this a...

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Section: Discussionmentioning

confidence: 99%

Contributions of Five Secondary Metal Uptake Systems to Metal Homeostasis of Cupriavidus metallidurans CH34

et al. 2011

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“…Tungstendependent enzymes were mainly found in anaerobic, thermophilic bacteria and archaea present in deep-sea hydrothermal vents, where tungsten is enriched. In most other habitats, tungsten is usually 100-fold less abundant than molybdenum (Hille, 2002;Schwarz et al, 2007). Recently, tungsten-dependent enzymes were also found in aerobic bacteria, e.g.…”

Section: Discussionmentioning

confidence: 99%

Corynebacterium glutamicum harbours a molybdenum cofactor-dependent formate dehydrogenase which alleviates growth inhibition in the presence of formate

et al. 2012

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“…Similarly, although most copper-containing enzymes of E. coli are periplasmic or have their copper sites exposed to the periplasm, the presence of cytoplasmic copper proteins cannot be excluded. Examples of these are YhcH (54) and factors involved in molybdenum cofactor biosynthesis (46). Therefore, flux control is needed for these two RND-driven efflux pumps to prevent situations of metal starvation, similar to the flux control that fine-tunes the activity of other metal transporters (31).…”

Section: Transenvelope Efflux By Metal-transporting Rnd Proteins?mentioning

confidence: 99%

Switch or Funnel: How RND-Type Transport Systems Control Periplasmic Metal Homeostasis

et al. 2011

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Bacteria have evolved several transport mechanisms to maintain metal homeostasis and to detoxify the cell. One mechanism involves an RND (resistance-nodulation-cell division protein family)-driven tripartite protein complex to extrude a variety of toxic substrates to the extracellular milieu. These efflux systems are comprised of a central RND proton-substrate antiporter, a membrane fusion protein, and an outer membrane factor. The mechanism of substrate binding and subsequent efflux has yet to be elucidated. However, the resolution of recent protein crystal structures and genetic analyses of the components of the heavy-metal efflux family of RND proteins have allowed the developments of proposals for a substrate transport pathway. Here two models of substrate extrusion through RND protein complexes of the heavy-metal efflux protein family are described. The funnel model involves the shuttling of periplasmic substrate from the membrane fusion protein to the RND transporter and further on through the outer membrane factor to the extracellular space. Conversely, the switch model requires substrate binding to the membrane fusion protein, inducing a conformational change and creating an open-access state of the tripartite protein complex. The extrusion of periplasmic substrate bypasses the membrane fusion protein, enters the RND-transporter directly via its substrate-binding site, and is ultimately eliminated through the outer membrane channel. Evidence for and against the two models is described, and we propose that current data favor the switch model.In Gram-negative bacteria, RND-driven tripartite protein complexes pump out a wide array of substrates. The RND (resistance-nodulation-cell division) protein superfamily can be divided into seven protein families with members being involved in transport of organic substances, transition metals, and polypeptides (55). Two RND families have been most extensively studied. The hydrophobe/amphiphile efflux family includes the RND proteins AcrB from Escherichia coli and MexB from Pseudomonas aeruginosa, both of which are involved in export of organic substances such as various antibiotics, bile salts, and other hydrophobic substances. The heavy metal efflux family contains metal transporters, such as CzcA from Cupriavidus metallidurans strain CH34 and CusA from E. coli. The nonspecificity of the RND proteins exporting organic substances has made elucidation of the actual transport pathway and pump regulation difficult. In contrast, metal-transporting RND proteins have a limited substrate spectrum, pumping out either the monovalent cations Cu(I) and Ag(I) or divalent cations of the transition metals Zn(II), Ni(II), Co(II), and sometimes the heavy metal cation Cd(II) (9, 25, 33). Since metals bind to very specific residues, the elucidation of the transport pathway should be easier.RND proteins utilize the proton motive force to drive the efflux of the substrates (14, 32). They form homotrimers (29) or heterotrimers composed of two different RND polypeptides in a 2:1 ratio (18...

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Molybdate and Tungstate: Uptake, Homeostasis, Cofactors, and Enzymes

Cited by 22 publications

References 117 publications

Contributions of Five Secondary Metal Uptake Systems to Metal Homeostasis of Cupriavidus metallidurans CH34

Contributions of Five Secondary Metal Uptake Systems to Metal Homeostasis of Cupriavidus metallidurans CH34

Corynebacterium glutamicum harbours a molybdenum cofactor-dependent formate dehydrogenase which alleviates growth inhibition in the presence of formate

Switch or Funnel: How RND-Type Transport Systems Control Periplasmic Metal Homeostasis

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