Molybdenum transport in plants and animals
See also molybdoenzymes, molybdenum storage proteins, molybdo-pterin, Mo co-factor
Molybdenum transport as molybdate and comparison with sulfate. Preventing extracellular uptake by complexing.
It is likely that molybdenum is taken up and transported in plants and animals in the form of the simple molybdate ion [MoO4]2-. In sheep [Scaife, 1956] molybdenum in the blood and urine is readily dialysable and is entirely anionic. A study of molybdenum toxicity in the microorganism Salmonella typhimurium has indicated that molybdate and sulfate are transported in the same system [McKillen and Spencer, 1970]. In this organism uptake of molybdenum and molybdenum toxicity are prevented by complexing of extracellular molybdate with L-cysteine and reduced glutathione. However, it has also been suggested that in the microorganism Aspergillus nidulans molybdenum is taken up in a phosphorylated entity and a carbohydrate [Arst et al., 1970; Arst and Cove, 1970]. The following chelating agents have been reported to be effective against molybdenum toxicity in mice (presumably because they coordinate with the molybdate ion): ethylenediaminetetraacetate, diethylenetriaminepentaacetate, unithiol and deoxycholate [Chem. Abs,1971]
Scaife, J. F., New Zealand J. Sci. Technol., 1956, 38A ,293.
McKillen, M. N.and Spencer, B., Biochem. J., 1970, 118 , 27.
Arst, H. N., MacDonald, D. W. and Cove, D. J., Mol. Gen. Genet., 1970, 108 , 129.
Arst, H. N. and Cove, D. J., Mol. Gen. Genet., 1970, 108 , 146.Chem. Abs., 1971, 74 , 99958u.
Multiplicity of Sulfate and Molybdate Transporters and Their Role in Nitrogen Fixation in Rhizobium leguminosarum bv. viciae Rlv3841
Rhizobium leguminosarum Rlv3841 contains at least three sulfate transporters, i.e., SulABCD, SulP1 and SulP2, and a single molybdate transporter, ModABC. SulABCD is a high-affinity transporter whose mutation prevented growth on a limiting sulfate concentration, while SulP1 and SulP2 appear to be low-affinity sulfate transporters. ModABC is the sole high-affinity molybdate transport system and is essential for growth with NO3- as a nitrogen source on limiting levels of molybdate (molybdate, a quadruple mutant with all four transporters inactivated, had the longest lag phase on NO3-, suggesting these systems all make some contribution to molybdate transport. Growth of Rlv3841 on limiting levels of sulfate increased sulB, sulP1, modB, and sulP2 expression 313.3-, 114.7-, 6.2-, and 4.0-fold, respectively, while molybdate starvation increased only modB expression (three- to 7.5-fold). When grown in high-sulfate but not low-sulfate medium, pea plants inoculated with LMB695 (modB) reduced acetylene at only 14% of the wild-type rate, and this was not further reduced in the quadruple mutant. Overall, while modB is crucial to nitrogen fixation at limiting molybdate levels in the presence of sulfate, there is an unidentified molybdate transporter also capable of sulfate transport.
Cheng, G., Karunakaran, R., East, A. K., and Poole, P. S.,Multiplicity of Sulfate and Molybdate Transporters and Their Role in Nitrogen Fixation in Rhizobium leguminosarum bv. viciae Rlv3841, Molecular plant-microbe interactions : MPMI, 2016, 29, 143-52.
Microbial ligand coordination: Consideration of biological significance
Siderophores are generally considered to be microbial chelating compounds secreted by bacteria to facilitate uptake of iron(III). Certain siderophores, however, have a high affinity for other transition metal ions, including manganese(III), copper(II), molybdenum(VI), and vanadium(V). A new class of microbial ligands produced by methanotrophs, called chalkophores, is produced to facility copper uptake.
This review considers the coordination of siderophores to Mn(III), Cu(II/I), Mo(VI) and V(V), and their stability constants relative to Fe(III), when available, as well as the coordination complexes of chalkophores to Cu( l). (C) 2015 Elsevier B.V. All rights reserved.
Springer, S. D., and Butler, A.,Microbial ligand coordination: Consideration of biological significance, Coordination Chemistry Reviews, 2016, 306, 628-635.
ATP-binding cassette (ABC) transporters and homeostasis
Designating ligand specificities to metal uptake ABC transporters in Thermus thermophilus HB8
Micronutrients such as metal ions are indispensable for the growth and survival of microorganisms in assorted environmental niches. However, change in cellular concentration of metal ions is pernicious for an organism; thus metal ion homeostasis is crucial for their survival and growth. An eminent mechanism for maintaining metal ion homeostasis in microorganisms is ATP-binding cassette (ABC) transporters, which transport metal ions in their ionic/complex forms across the cell membrane. For the uptake, metals are sequestered by substrate-binding proteins (SBPs) and transferred to transmembrane domains (TMDs) for their transport. In this work, a high-throughput data mining analysis has been performed to identify open reading frames (ORFs) encoding metal-specific ABC transporters in a thermophilic bacterium Thermus thermophilus HB8. In total, 22 ORFs resulting in eight ABC transport systems were identified, which are potentially involved in the uptake of metal ions. This study suggests that three out of eight metal-specific ABC import systems are specific to iron ions. Among the remaining five, two are particular to divalent metal ions such as Mg2+ and Zn2+/Mn2+, another two are for tetrahedral oxyanions such as MoO42- and WO42- and the remaining one imports cyanocobalamin (vitamin B12). Besides these, the results of this study demonstrate the existence of a mechanism where TMD and NBD components are shared among different ABC transport systems hinting that multiple substrates can be imported via a single transporter. This study thus provides the first ever preliminary glimpse into the entire repertoire of metal uptake ABC transporters in a thermophilic organism.
S. K. Mandal, R. Adhikari, A. Sharma, M. Chandravanshi, P. Gogoi, and S. P. Kanaujia,Designating ligand specificities to metal uptake ABC transporters in Thermus thermophilus HB8, Metallomics, 2019, 11, 597-612.
The Different Effects of Substrates and Nucleotides on the Complex Formation of ABC Transporters
The molybdate importer (ModBC-A of Archaeoglobus fulgidus) and the vitamin B12 importer (BtuCD-F of Escherichia coli) are members of the type I and type II ABC importer families. Here we study the influence of substrate and nucleotide binding on complex formation and stability. Using native mass spectrometry we show that the interaction between the periplasmic substrate-binding protein (SBP) ModA and the transporter ModBC is dependent upon binding of molybdate. By contrast, vitamin B12 disrupts interactions between the transporter BtuCD and the SBP BtuF. Moreover, while ATP binds cooperatively to BtuCD-F, and acts synergistically with vitamin B12 to destabilize the BtuCD-F complex, no effect is observed for ATP binding on the stability of ModBC-A. These observations not only highlight the ability of mass spectrometry to capture these importer-SBP complexes but allow us to add molecular detail to proposed transport mechanisms.
F. Fiorentino, J. R. Bolla, S. Mehmood, and C. V. Robinson,The Different Effects of Substrates and Nucleotides on the Complex Formation of ABC Transporters, Structure (London, England : 1993), 2019, 27, 651-659.e3.
native mass spectrometry