title: Sequestration of a highly reactive intermediate in an evolving pathway for degradation of pentachlorophenol.
abstract: Microbes in contaminated environments often evolve new metabolic pathways for detoxification or degradation of pollutants. In some cases, intermediates in newly evolved pathways are more toxic than the initial compound. The initial step in the degradation of pentachlorophenol by Sphingobium chlorophenolicum generates a particularly reactive intermediate; tetrachlorobenzoquinone (TCBQ) is a potent alkylating agent that reacts with cellular thiols at a diffusion-controlled rate. TCBQ reductase (PcpD), an FMN- and NADH-dependent reductase, catalyzes the reduction of TCBQ to tetrachlorohydroquinone. In the presence of PcpD, TCBQ formed by pentachlorophenol hydroxylase (PcpB) is sequestered until it is reduced to the less toxic tetrachlorohydroquinone, protecting the bacterium from the toxic effects of TCBQ and maintaining flux through the pathway. The toxicity of TCBQ may have exerted selective pressure to maintain slow turnover of PcpB (0.02 s(-1)) so that a transient interaction between PcpB and PcpD can occur before TCBQ is released from the active site of PcpB.
authors.affiliation: Department of Molecular, Cellular and Developmental Biology and Cooperative Institute for Research in Environmental Sciences, University of Colorado, Boulder, CO 80309, USA.
authors.forename: Itamar
authors.initials: I
authors.lastname: Yadid
authors.forename: Johannes
authors.initials: J
authors.lastname: Rudolph
authors.forename: Klara
authors.initials: K
authors.lastname: Hlouchova
authors.forename: Shelley D
authors.initials: SD
authors.lastname: Copley
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D055162:Biocatalysis; D001673:Biodegradation, Environmental; D002703:Chloranil / Q000031:analogs & derivatives* / Q000737:chemistry / Q000378:metabolism; D005486:Flavin Mononucleotide / Q000378:metabolism; D006873:Hydroquinones / Q000737:chemistry / Q000378:metabolism*; D007700:Kinetics; D053858:Metabolic Networks and Pathways; D006899:Mixed Function Oxygenases / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D015394:Molecular Structure; D009154:Mutation; D009243:NAD / Q000378:metabolism; D010084:Oxidation-Reduction; D010416:Pentachlorophenol / Q000737:chemistry / Q000378:metabolism*; D011485:Protein Binding; D011808:Quinone Reductases / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D042301:Sphingomonadaceae / Q000235:genetics / Q000378:metabolism*; D013379:Substrate Specificity
chemical_list: D001426:Bacterial Proteins; D006873:Hydroquinones; D002703:Chloranil; D009243:NAD; D005486:Flavin Mononucleotide; C044578:2,3,5,6-tetrachlorohydroquinone; D010416:Pentachlorophenol; D006899:Mixed Function Oxygenases; C069781:pentachlorophenol monooxygenase; D011808:Quinone Reductases; C000594018:tetrachlorobenzoquinone reductase, Sphingobium chlorophenolicum; C039499:2-chloranil
keywords: biodegradation; channeling; molecular evolution; quinone reductase