Molybdenum-containing arsenite oxidase of the chemolithoautotrophic arsenite oxidizer NT-26
| Autor: | Joanne M. Santini, Rachel N. vanden Hoven |
|---|---|
| Rok vydání: | 2004 |
| Předmět: |
Arsenites
Molecular Sequence Data Glycerol transport chemistry.chemical_element Biology Microbiology Gram-Negative Chemolithotrophic Bacteria chemistry.chemical_compound Amino Acid Sequence Molecular Biology Arsenic Arsenite Alphaproteobacteria Molybdenum Oxidase test Alcaligenes faecalis Aroa Arsenate Periplasmic space Sequence Analysis DNA biology.organism_classification Enzymes and Proteins Mutagenesis Insertional chemistry Biochemistry Periplasm Oxidoreductases Oxidation-Reduction |
| Zdroj: | Journal of bacteriology. 186(6) |
| ISSN: | 0021-9193 |
| Popis: | The chemolithoautotroph NT-26 oxidizes arsenite to arsenate by using a periplasmic arsenite oxidase. Purification and preliminary characterization of the enzyme revealed that it (i) contains two heterologous subunits, AroA (98 kDa) and AroB (14 kDa); (ii) has a native molecular mass of 219 kDa, suggesting an 22 configuration; and (iii) contains two molybdenum and 9 or 10 iron atoms per 22 unit. The genes that encode the enzyme have been cloned and sequenced. Sequence analyses revealed similarities to the arsenite oxidase of Alcaligenes faecalis, the putative arsenite oxidase of the beta-proteobacterium ULPAs1, and putative proteins of Aeropyrum pernix, Sulfolobus tokodaii, and Chloroflexus aurantiacus. Interestingly, the AroA subunit was found to be similar to the molybdenum-containing subunits of enzymes in the dimethyl sulfoxide reductase family, whereas the AroB subunit was found to be similar to the Rieske iron-sulfur proteins of cytochrome bc1 and b6f complexes. The NT-26 arsenite oxidase is probably exported to the periplasm via the Tat secretory pathway, with the AroB leader sequence used for export. Confirmation that NT-26 obtains energy from the oxidation of arsenite was obtained, as an aroA mutant was unable to grow chemolithoautotrophically with arsenite. This mutant could grow heterotrophically in the presence of arsenite; however, the arsenite was not oxidized to arsenate. Arsenic is ubiquitous in the environment and is most commonly found in an insoluble form associated with rocks and minerals (11). In soluble forms, arsenic occurs as trivalent arsenite [As(III)] and pentavalent arsenate [As(V)]. Arsenate, a phosphate analogue, can enter cells via the phosphate transport system and is toxic because it can interfere with normal phosphorylation processes by replacing phosphate. It was recently demonstrated that arsenite enters cells at a neutral pH by aqua-glyceroporins (glycerol transport proteins) in bacteria, yeasts, and mammals (23, 39), and its toxicity lies in its ability to bind sulfhydryl groups of cysteine residues in proteins, thereby inactivating them. Arsenite is considered to be more toxic than arsenate and can be oxidized to arsenate chemically or microbially (12, 16). |
| Databáze: | OpenAIRE |
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