Room: BLS 443
Room: BLS 440
Research & Interests
Our research is focused on how microorganisms transform environmental pollutants. We have worked on the biochemistry of polychlorophenol biodegradation, chelating-agent biodegradation, and chromate biotransformation.
Metabolic pathways of environmental pollutants. Synthetic organic chemicals have a variety of industrial, agricultural and domestic applications. Their wide usage has also created many environmental problems, as some of them are highly toxic and persistent in the environment. Fortunately, microorganisms have evolved rapidly to degrade many of the synthetic compounds; however, they are not efficient in degrading some highly recalcitrant polychlorinated compounds, due to the presence of chlorine in their structures. We have characterized three novel polychlorophenol degradation pathways. In addition, we have contributed to the complete elucidation of the metabolic pathways for two chelating agents, EDTA and nitrilotriacetate, which are not toxic by themselves, but they can mobilize insoluble radionuclides and heavy metals through groundwater. The purposes are to understand the metabolic pathways that have evolved and to construct new pathways for similar compounds that are not naturally biodegradable.
Characterization of novel enzymes. During investigation of metabolic pathways, we have discovered several new types of enzymes and enzymes that have been evolved from existing enzymes to perform dechlorination. Our hypothesis is that some of the enzymes have been quickly evolved after exposure to the environmental pollutants that did not previously exit in nature and they can be improved. Our current efforts are characterizing the enzymatic mechanisms and determine their structural and functional features. Our future research include protein engineering to make more efficient enzymes for catalysis, guided by structures and reaction mechanisms. The improved enzymes can be introduced back into microorganisms to enhance their ability to degrade environmental pollutants.
The formation of soluble organo-Cr(III) after chromate bioreduction. Heavy metal contamination is another concern for public health. The general approach to metal bioremediation is to reduce their solubility, preventing spreading through groundwater. We have investigated the biochemistry of chromate reduction by microorganisms. The general accepted concept was that toxic chromate was reduced to nontoxic Cr(OH)3 precipitates. To our surprise, we did not find Cr(OH)3 precipitates but soluble organo-Cr(III) complexes after chromate reduction by microorganisms, enzymes, or reducing chemicals. The organo-Cr(III) is formed and stable due to the inert nature of Cr(III) in ligand exchange. Our work on soluble organo-Cr(III) is well received and it is a new component in the biogeochemical cycling of chromium.
- Xu P, H. Yu, A. M. Chakrabarty, L. Xun. (2013) Genome Sequence of the 2,4,5-Trichlorophenoxyacetate-Degrading Bacterium Burkholderia phenoliruptrix Strain AC1100. Genome Announc. 1(4). doi:pii: e00600-13.10.1128/genomeA.00600-13. PMID: PMCID:
- Hayes, R.P., A.R. Green, M. S. Nissen, K. M. Lewis, L. Xun, C. Kang. (2013) Structural characterization of 2,6-dichloro-p-hydroquinone 1,2-dioxygenase (PcpA) from Sphingobium chlorophenolicum, a new type of aromatic ring-cleavage enzyme. Mol Microbiol. 88:523-536. doi: 10.1111/mmi.12204. PMID: PMCID:
- Green, A.R., R.P. Hayes, L. Xun, and C. Kang. (2012) Structural understanding of the glutathione-dependent reduction mechanism of glutathionyl-hydroquinone reductases. J. Biol. Chem. 287:35838-35848. doi: 10.1074/jbc.M112.395541. PMID: PMCID:
- Hayes, R.P., B.N. Webb, A.K. Subramanian, M. Nissen, A. Popchock, L. Xun, and C. Kang. (2012) Structural and Catalytic Differences between Two FADH2-Dependent Monooxygenases: 2,4,5-TCP 4-Monooxygenase (TftD) from Burkholderia cepacia AC1100 and 2,4,6-TCP 4-Monooxygenase (TcpA) from Cupriavidus necator JMP134. Int. J. Mol. Sci. 3:9769-9784. doi:10.3390/ijms1308976 PMID: PMCID:
- Lam, L.K.M., Z. ZHANG, P. G. Board, L. Xun. (2012) Reduction of benzoquinones to hydroquinones via spontaneous reaction with glutathione and enzymatic reaction by S-Glutathionyl-hydroquinone reductases. Biochemistry. 51:5014−5021. doi:10.1021/bi300477z. PMID: PMCID:
- Kang, C., R. Hayes, E. J. Sanchez, B.N. Webb, Q. Li, T. Hooper, M. S Nissen, and L. Xun. (2012) Furfural reduction mechanism of a zinc-dependent alcohol dehydrogenase from Cupriavidus necator JMP134. Mol. Microbiol. 83(1):85-95. doi: 10.1111/j.1365-2958.2011.07914.x. PMID: PMCID:
- Li, Q., L. K. M. Lam, L. Xun. (2011) Cupriavidus necator JMP134 rapidly reduces furfural with a Zn-dependent alcohol dehydrogenase. Biodegrad. 22:1215–1225. doi: 10.1007/s10532-011-9476-y. PMID: PMCID:
- Li, Q., L.K.M. Lam, L. Xun. (2011) Biochemical characterization of ethanol-dependent reduction of furfural by alcohol dehydrogenases. Biodegrad. 22:1227–1237. doi: 10.1007/s10532-011-9477-x. PMID: PMCID:
- Belchik, S.M., and L. Xun. (2011) S-Glutathionyl-(chloro)hydroquinone reductases: a new class of glutathione transferases functioning as oxidoreductases. Drug Metabolism Review. 43:307-316. doi: 10.3109/03602532.2011.552909. PMID: PMCID:
- Dwivedi, P., G. Puzon, M. Tam, D. Langlais, S. Jackson, K. Kaplan, W.F. Siems, A.J. Schultz, L. Xun, A. Woods, H.H. Hill, Jr. (2010) Metabolic profiling of Escherichia coli by ion mobility-mass spectrometry with MALDI ion source. J Mass Spectrom. 45:1383-93. PMID: PMCID:
- Xun, L., S. Belchik, R. Xun, Y. Huang, H. Zhou, E. Sanchez, C. Kang, P. G. Board. (2010) S-Glutathionyl-(chloro)hydroquinone reductases: a novel class of glutathione transferases in bacteria and fungi. Biochem J. 428:419-427. PMID: PMCID:
- Webb, B. N., J. W. Ballinger, E. Kim, S. M. Belchik, K. S. Lam, B. Youn, M. S. Nissen, L. Xun, and C. Kang. (2010) Characterization of chlorophenol 4-monooxygenase (TftD) and NADH:FAD oxidoreductase (TftC) of Burkholderia cepacia AC1100. J Biol Chem. 285:2014-27. PMID: PMCID:
- Belchik, S. M., S. Schaeffer, S. Hasenoehrl, and L. Xun. (2010) A b-barrel outer membrane protein (TcpY) facilitates cellular uptake of polychlorophenols in the gram negative bacterium Cupriavidus necator. Biodegradation. 21:431-439. PMID: PMCID:
- Liu H., Y. Xin, and L. Xun. (2014) Distribution, diversity and activities of sulfur dioxygenases in heterotrophic bacteria. Appl Environ Microbiol. 80:1799-1806. doi:10.1128/AEM.03281-13. PMID: PMCID:
- Hayes R.P., T.W. Moural, K.M. Lewis, D. Onofrei, L. Xun, and C. Kang. (2014) Structures of the inducer-binding domain of pentachlorophenol-degrading gene regulator PcpR from Sphingobium chlorophenolicum. Int J Mol Sci. 15:20736-52. doi: 10.3390/ijms151120736. PMID: PMCID:
- Xia Y., W. Chu, Q. Qi, and L. Xun. (2015) New insights into the QuikChangeTM process guide the use of Phusion DNA polymerase for site-directed mutagenesis. Nucleic Acids Res. 43(2):e12. doi: 10.1093/nar/gku1189. PMID: PMCID:
- Sattler S.A., X. Wang, K.M. Lewis, P.J. DeHan, C.M. Park, Y. Xin, H. Liu, M. Xian, L. Xun, and C. Kang. (2015) Characterizations of Two Bacterial Persulfide Dioxygenases of the Metallo-β-lactamase Superfamily. JBC 290. 18914-18923. PMID: PMCID:
- Zhang Z., S.B. Clark, L. Rao, G.J. Puzon, L. Xun. (2016) Further structural analysis of Cr(III) oligomers in weakly acidic solutions. Polyhedron. 105:77-83. PMID: PMCID:
- Jun S.Y., K.M. Lewis, B. Youn, L. Xun, C. Kang. (2016) Structural and biochemical characterization of EDTA monooxygenase and its physical interaction with a partner flavin reductase. Mol Microbiol. 100:989-1003. doi: 10.1111/mmi.13363. PMID: PMCID:
- Xin Y., H. Liu, F. Cui, H. Liu, L. Xun. (2016) Recombinant Escherichia coli with sulfide: Quinone oxidoreductase and persulfide dioxygenase rapidly oxidizes sulfide to sulfite and thiosulfate via a new pathway. Environ Microbiol. 18:5123-5136. PMID: PMCID:
- Xia Y., and L. Xun. (2017) Revised Mechanism and Improved Efficiency of the QuikChange Site-Directed Mutagenesis Method. Methods Mol Biol. 1498:367-374. PMID: PMCID: