Dr. Luying Xun
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.
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.
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.
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. 13:9769-9784. doi:10.3390/ijms13089769.
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.
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.
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.
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.
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.
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.
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.
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.
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.
Nissen, M. S., B. Youn, B. D. Knowles, J. W. Ballinger, S.-Y. Jun, S. M. Belchik, L. Xun, and C. Kang. 2008. Crystal structures of NADH:FMN oxidoreductase (EmoB) at different stages of catalysis. J. Biol. Chem. In press (doi:10.1074/jbc.M804535200).
Huang, Y., R. Xun, G. Chen, and L. Xun. 2008. The maintenance role of a glutathionyl-hydroquinone lyase (PcpF) in pentachlorophenol degradation by Sphingobium chlorophenolicum ATCC 39723. J. Bacteriol. In press (doi:10.1128/JB.00489-08).
Belchik, S. M., and L. Xun. 2008. Functions of flavin reductase and quinone reductase in 2,4,6-trichlorophenol degradation by Cupriavidus necator JMP134. J. Bacteriol. 190:1615-1619.
Tokala, R. K., D. R. Yonge, G. J. Puzon, V. Sivaswamy, L. Xun, and B. M. Peyton. 2008. Subsurface Mobility of Organo-Cr(III) Complexes Formed During Biological Reduction of Cr(VI). J. Environ. Engineer. 134:87-92.
Prabha Dwivedi, P., P. Wu, S. J. Klopsch, G. J. Puzon, L. Xun, and H. H. Hill Jr. 2008. Metabolic profiling by ion mobility mass spectrometry. Metabolomics. 4:63-80.
Puzon, G. J., R. K. Tokala, H. Zhang, D. R. Yonge, B. M. Peyton, and L. Xun. 2008. Mobility and recalcitrance of organo-chromium(III) complexes. Chemosphere. 70:2054-2059.
Puzon, G. J., Y. Huang, A. Dohnalkova, and L. Xun. 2008. Isolation and characterization of an NAD+-degrading bacterium PTX1 and its role in chromium biogeochemical Cycle. Biodegradation. 19:417-424.
Zhang, H., J. P. Herman, H. Bolton, Jr., Z. Zhang, S. Clark, and L. Xun. 2007. Evidence indicating that a bacterial ABC-type transporter imports free EDTA for metabolism. J. Bacteriol. 189:7991-7997.
Bohuslavek1, J., S. Chanama, R. L. Crawford, and L. Xun. 2005. Identification and Characterization of Hydroxyquinone Hydratase Activities from Sphingobium chlorophenolicum ATCC 39723. Biodegradation. 16:353-362.
Puzon, G. J., A. G. Roberts, D. M. Kramer, and L. Xun. 2005. Formation of soluble organo-chromium(III) complexes after chromate reduction in the presence of cellular organics. Environ. Sci. Technol. 39:2811-2817
Xun, L., and C. M. Webster. 2004. A monooxygenase catalyzes sequential dechlorinations of 2,4,6-trichlorophenol by oxidative and hydrolytic reactions. J. Biol. Chem. 279:6696-6700.
Gisi, M. R. and L. Xun. 2003. Characterization of chlorophenol 4-Monooxygenase (TftD) and NADH:FAD oxidoreductase (TftC) of Burkholderia cepacia AC1100. J. Bacteriol. 185:2786-2792.
Louie, T. M., X. S. Xie, and L. Xun. 2003. Coordinated production and utilization of FADH 2 by NAD(P)H-flavin oxidoreductase and 4-hydroxyphenylacetate 3-monooxygenase. Biochemistry 42:7509-7517.
Yang, H., G. Luo, P. Karnchanaphanurach, T. M. Louie, L. Xun, and X. S. Xie. 2003. Protein conformational dynamics probed by single-molecule electron transfer. Science 302:262-266.
Liu Y, Y. Liu, Y. Dai, L. Xun, and M. Hu. 2003. Enteric disposition and recycling of flavonoids and ginkgo flavonoids. J. Altern. Complement. Med. 9:631-40.
Louie, T. M., C. M. Webster, and L. Xun. 2002. Genetic and biochemical characterization of a novel 2,4,6-trichlorophenol degradation pathway in Ralstonia eutropha JMP134. J. Bacteriol. 184:3492-3500.
Puzon, G. J., J. N. Petersen, A. G. Roberts, D. M. Kramer, and L. Xun. 2002. A bacterial flavin reductase system reduces chromate to a soluble chromium(III)-NAD+ complex. Biochem. Biophys. Res. Comm. 294:76-81.
Cai, M, and L. Xun. 2002. Organization and regulation of pentachlorophenol-degrading genes in Sphingobium chlorophenolicum ATCC 39723. J. Bacteriol. 184:4672-4680.
Louie, T. M., H. Yang, P. Karnchanaphanurach, X. S. Xie, and L. Xun. 2002. FAD is a preferred substrate and an inhibitor of Escherichia coli general NAD(P)H:flavin oxidoreductase. J. Biol. Chem. 277: 39450-39455.
Bohuslavek, J., J. Payne, Y. Liu, H. Bolton, Jr., and L. Xun. 2001. Cloning, sequencing and characterization of a gene cluster involved in EDTA degradation from the bacterium BNC1. Appl. Environ. Microbiol. 67:688-695.
Liu, Y., T. M. Louie, J. Payne, J. Bohuslavek, H. Bolton, Jr., and L. Xun. 2001. Identification, purification and characterization of iminodiacetate oxidase from the EDTA-degrading bacterium BNC1. Appl. Environ. Microbiol. 67:696-701.
Vanbriesen, J. M., B. E. Bittmann, L. Xun, D. C. Girvin, and H. Bolton, Jr. 2000. The rate-controlling substrate of nitrilotriacetate for biodegradation by Chelatobacter heintzii. Environ. Sci. Technol. 34:3346-3353.