title: Exploring the biochemical properties and remediation applications of the unusual explosive-degrading P450 system XplA/B.
abstract: Widespread contamination of land and groundwater has resulted from the use, manufacture, and storage of the military explosive hexa-hydro-1,3,5-trinitro-1,3,5-triazine (RDX). This contamination has led to a requirement for a sustainable, low-cost method to remediate this problem. Here, we present the characterization of an unusual microbial P450 system able to degrade RDX, consisting of flavodoxin reductase XplB and fused flavodoxin-cytochrome P450 XplA. The affinity of XplA for the xenobiotic compound RDX is high (K(d) = 58 muM) and comparable with the K(m) of other P450s toward their natural substrates (ranging from 1 to 500 muM). The maximum turnover (k(cat)) is 4.44 per s, only 10-fold less than the fastest self-sufficient P450 reported, BM3. Interestingly, the presence of oxygen determines the final products of RDX degradation, demonstrating that the degradation chemistry is flexible, but both pathways result in ring cleavage and release of nitrite. Carbon monoxide inhibition is weak and yet the nitroaromatic explosive 2,4,6-trinitrotoluene (TNT) is a potent inhibitor. To test the efficacy of this system for the remediation of groundwater, transgenic Arabidopsis plants expressing both xplA and xplB were generated. They are able to remove saturating levels of RDX from liquid culture and soil leachate at rates significantly faster than those of untransformed plants and xplA-only transgenic lines, demonstrating the applicability of this system for the phytoremediation of RDX-contaminated sites.
authors.affiliation: Center for Novel Agricultural Products, Department of Biology, University of York, York, United Kingdom.
authors.forename: Rosamond G
authors.initials: RG
authors.lastname: Jackson
authors.forename: Elizabeth L
authors.initials: EL
authors.lastname: Rylott
authors.forename: Diane
authors.initials: D
authors.lastname: Fournier
authors.forename: Jalal
authors.initials: J
authors.lastname: Hawari
authors.forename: Neil C
authors.initials: NC
authors.lastname: Bruce
mesh_terms: D000693:Anaerobiosis; D017360:Arabidopsis / Q000235:genetics; D001426:Bacterial Proteins / Q000037:antagonists & inhibitors / Q000302:isolation & purification / Q000378:metabolism*; D001673:Biodegradation, Environmental; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000302:isolation & purification / Q000378:metabolism*; D010084:Oxidation-Reduction; D030821:Plants, Genetically Modified; D011994:Recombinant Proteins / Q000378:metabolism; D012240:Rhodococcus / Q000201:enzymology*; D013056:Spectrophotometry, Ultraviolet; D014227:Triazines / Q000378:metabolism*
chemical_list: D001426:Bacterial Proteins; D065607:Cytochrome P-450 Enzyme Inhibitors; D011994:Recombinant Proteins; D014227:Triazines; D003577:Cytochrome P-450 Enzyme System; C009160:cyclonite