Part:BBa_K2194000

chrR6 Chromate Reductase Enzyme

The chrR6 protein is a mutated/enhanced version (^Tyr128^Asn) of the chrR enzyme originally found in Escherichia coli. It has chromate and uranyl reductase activity. BioBrick BBa_K2194000 contains only the cds for this protein.

Biology and Usage

The chrR6 enzyme is a mutated and enhanced version (^Tyr128^Asn) of the soluble chrR enzyme originally found in Escherichia coli and Pseudomonas putida. It has chromate and uranyl reductase activity. The enzyme chrR6 reduces hexavalent chromium (Cr(VI)) directly to trivalent chromium (Cr(III)) without producing an unstable pentavalent chromium (Cr(V)) intermediate and minimizing generation of toxic reactive oxygen species. [1]

As determined from studies on purified enzymes [1], ^Tyr128^Asn substitution increases the rate of Cr(VI) reduction from 295 ± 27 nmol mg protein^-1 min^-1, as observed for chrR, to 8,812 ± 611 nmol mg protein^-1 min^-1. Observed K_cat/K_m values are 4.5 × 10⁴ ± 3 × 10³ for chrR and 1.3 × 10⁷ ± 3 × 10⁵ for chrR6 [1]. When the activity of chrR6 and chrR was studied in vivo in soil bacteria P. putida, no enhanced chromium or uranium reduction activity was observed for chrR6 transformed bacteria, which led to the conclusion that limited cell permeability to Cr(VI) prevents the reduction activity.

Figure 1 shows the rate of Cr(VI) reduction by E. coli<i> MG1655 transformed with chrR6 and sulfate transport system cysPUWA vs. the rate of Cr(VI) reduction by wild type E. coli

Figure 1: rate of Cr(VI) reduction by E. coli MG1655 transformed with <i> chrR6 </i> and sulfate transport system <i> cysPUWA. </i>

Figure 2 shows the total amount of Cr(VI) reduced by <i>E. coli<i> MG1655 transformed with chrR6 and sulfate transport system cysPUWA and the rate of Cr(VI) reduction by wild type E. coli

Figure 2: the amount of Cr(VI) reduced by E. coli MG1655 transformed with <i> chrR6 </i> and <i> cysPUWA</i> wild-type <i> E. coli </i>

[1] Barak, Y. et al. “Analysis of Novel Soluble Chromate and Uranyl Reductases and Generation of an Improved Enzyme by Directed Evolution.” Applied and Environmental Microbiology 72.11 (2006): 7074–7082. Web.
[2] Robins, Katherine J. et al. “Escherichia Coli Nema Is an Efficient Chromate Reductase That Can Be Biologically Immobilized to Provide a Cell Free System for Remediation of Hexavalent Chromium.” PLoS ONE (2013): n. pag. Web.
[3] Cheung, K. H., and Ji Dong Gu. “Mechanism of Hexavalent Chromium Detoxification by Microorganisms and Bioremediation Application Potential: A Review.” International Biodeterioration and Biodegradation 59.1 (2007): 8–15. Web.

Sequence and Features

Assembly Compatibility:

• 10
  COMPATIBLE WITH RFC[10]
• 12
  COMPATIBLE WITH RFC[12]
• 21
  INCOMPATIBLE WITH RFC[21]

  Illegal BglII site found at 570
  
• 23
  COMPATIBLE WITH RFC[23]
• 25
  INCOMPATIBLE WITH RFC[25]

  Illegal AgeI site found at 337
  
• 1000
  INCOMPATIBLE WITH RFC[1000]

  Illegal BsaI site found at 3
  Illegal BsaI.rc site found at 583