Perchlorate reductase

Perchlorate reducatase is an enzyme that catalyzes the chemical reactions:

ClO₄⁻ + 2 AH₂ $\rightleftharpoons$ ClO₂⁻ + 2 A + 2 H₂O

and

ClO₃⁻ + AH₂ $\rightleftharpoons$ ClO₂⁻ + A + H₂O

Thus, the substrates of this enzyme are a reduced electron acceptor (denoted AH₂) and either chlorate or perchlorate, sometimes collectively denoted as (per)chlorate. The products are chlorite, an oxidized electron acceptor (denoted A), and water. It is closely related to the enzyme chlorate reductase, but is distinguished by its ability to reduce both perchlorate and chlorate, whereas chlorate reductase only acts on chlorate. Perchlorate reductase and chlorate reductase are closely related but form genetically distinct clades.^[1]

As of November 2014, perchlorate reductase has not be assigned a specific Enzyme Commission number, but along with chlorate reductase (EC 1.97.1.1), it would presumably be a member of the EC 1.97.1.- oxidoreductase subclass. Some databases, including BRENDA, currently combine perchlorate reductase and chlorate reductase listings.^[2]

Structure

Perchlorate reductase is usually encoded as a combination of four genes, denoted pcrABCD.^[3] The active subunits are pcrA and pcrB which form a periplasmic dimer similar to the active complex in nitrate reductase. pcrC is a believed to be a c-type cytochrome that connects the AB complex to the membrane and allows for electron shuttling. The function of pcrD is uncertain, but may encode a molybdenum-containing chaperone protein specific to assembling the pcrABC system. All known functional perchlorate reductase enzymes include genetically similar versions of pcrABCD except for the epsilonproteobacteria Arcobacter strain CAB, which lacks a traditional pcrC and appears to have replaced it with an unrelated epsilonproteobacteria cytochrome.^[4]

All characterized organisms that encode perchlorate reductase also have the enzyme chlorite dismutase, which reduces the chlorite produced by perchlorate reductase, and prevents this reactive compound from accumulating to toxic levels. The pcrABCD and chlorite dismutase gene are typically located together in the bacterial genome.

References

1. Iain C. Clark, Ryan A. Melnyk, Anna Engelbrektson, John D. Coates (2013). "Structure and Evolution of Chlorate Reduction Composite Transposons". mBio 4 (4): e00379–13. doi:10.1128/mBio.00379-13.
2. "BRENDA listing for chlorate reductase".
3. Bender KS, Shang C, Chakraborty R, Belchik SM, Coates JD, Achenbach LA. (2005). "Identification, characterization, and classification of genes encoding perchlorate reductase". J Bacteriol 187 (15): 5090–6. doi:10.1128/jb.187.15.5090-5096.2005.
4. Carlström, Charlotte I.; Wang, Ouwei; Melnyk, Ryan A.; Bauer, Stefan; Lee, Joyce; Engelbrektson, Anna; Coates, John D. (2013). "Physiological and genetic description of dissimilatory perchlorate reduction by the novel marine bacterium Arcobacter sp. strain CAB". MBio 4 (3): e00217-13. doi:10.1128/mBio.00217-13.

• Benedict C. Okekea and William T. Frankenberger Jr. (2003). "Molecular analysis of a perchlorate reductase from a perchlorate-respiring bacterium Perc1ace". Microbiological Research 158 (4): 337–344. doi:10.1078/0944-5013-00213.
• Servé W. M. Kengen, Geoffrey B. Rikken, Wilfred R. Hagen, Cees G. van Ginkel, and Alfons J. M. Stams (November 1999). "Purification and Characterization of (Per)Chlorate Reductase from the Chlorate-Respiring Strain GR-1". J. Bacteriol. 181 (21): 6706–6711.