Subcellular localization of pentachlorophenol 4-monooxygenase in Sphingobium chlorophenolicum ATCC 39723

Effect of hexavalent chromium on the biodegradation of tetrabromobisphenol A (TBBPA) by Pycnoporus sanguineus

The influence of Cr(VI) on the degradation of tetrabromobisphenol A (TBBPA) by a typical species of white rot fungi, Pycnoporus sanguineus, was investigated in this study. The results showed that P. sanguineus together with its intracellular and extracellular enzyme could effectively degrade TBBPA. The degradation efficiency of TBBPA by both P. sanguineus and its enzymes decreased significantly when Cr(VI) concentration increased from 0 to 40 mg/L. The subsequent analysis about cellular distribution of TBBPA showed that the extracellular amount of TBBPA increased with the increment of Cr(VI) concentration, but the content of TBBPA inside fungal cells exhibited an opposite variation tendency. The inhibition of TBBPA degradation by P. sanguineus was partly attributed to the increase of cell membrane permeability and the decrease of cell membrane fluidity caused by Cr(VI). In addition, the decline of H⁺-ATPase and Mg²⁺-ATPase activities was also an important factor contributing to the suppression of TBBPA degradation in the system containing concomitant Cr(VI). Moreover, the activities of two typical extracellular lignin-degrading enzymes of P. sanguineus, MnP and Lac, were found to descend with ascended Cr(VI) level. Cr(VI) could also obviously suppress the gene expression of four intracellular enzymes implicated in TBBPA degradation, including two cytochrome P450s, glutathione S-transferases and pentachlorophenol 4-monooxygenase, which resulted in a decline of TBBPA degradation efficiency by fungal cells and intracellular enzyme in the presence of Cr(VI). Overall, this study provides new insights into the characteristics and mechanisms involved in TBBPA biodegradation by white rot fungi in an environment where heavy metals co-exist.

iTRAQ-based proteomic profiling of Pycnoporus sanguineus in response to co-existed tetrabromobisphenol A (TBBPA) and hexavalent chromium

In current study, we investigated the changes of proteome profiles of Pycnoporus sanguineus after a single exposure of Cr(VI), TBBPA and a combined exposure of TBBPA and Cr(VI), with the goal of illuminating the cellular mechanisms involved in the interactions of co-existed TBBPA and Cr(VI) with the cells of P. sanguineus at the protein level. The results revealed that some ATP-binding cassette (ABC) transporters were obviously induced by these pollutants to accelerate the transportation, transformation and detoxification of TBBPA and Cr(VI). Cr(VI) could inhibit the bioremoval of its organic co-pollutants TBBPA through suppressing the expression of several key proteins related to the metabolism of TBBPA by P. sanguineus, including two cytochrome P450s, pentachlorophenol 4-monooxygenase and glutathione S-transferases. Furthermore, Cr(VI) possibly reduced the cell vitality and growth of P. sanguineus by enhancing the expression of imidazole glycerol phosphate synthase as well as by decreasing the abundances of proteins associated with the intracellular metabolic processes, such as the tricarboxylic acid cycle, purine metabolism and glutathione biosynthesis, thereby adversely affecting the biotransformation of TBBPA. Cr(VI) also inhibited the expression of peptidyl prolyl cis/trans isomerases, thus causing the damage of cell membrane integrity. In addition, some important proteins participated in the resistance to Cr(VI) toxicity were observed to up-regulate, including heat shock proteins, 26S proteasome, peroxiredoxins and three critical proteins implicated in S-adenosyl methionine synthesis, which contributed to reducing the hazard of Cr(VI) to P. sanguineus. The results of this study provide novel insights into the physiological responses and molecular mechanism of white rot fungi P. sanguineus to the stress of concomitant TBBPA and Cr(VI).

Computer-aided modeling of pentachlorophenol 4-monooxygenase and site-directed mutagenesis of its active site

Homology modeling was used to construct a model of the three-dimensional structure of pentachlorophenol 4-monooxygenase (PcpB). A PSI-BLAST homology search was initially performed to identify the 3D structure of proteins homologous with PcpB. The feasibility of modeled structures of PcpB was evaluated by Verify3D, which calculated structural compatibility scores based on 3D-1D profiles. The predicted structure of PcpB had an acceptable 3D-1D self-compatibility score, beyond the incorrect fold score threshold. A PcpB-pentachlorophenol (PCP) complex was then constructed utilizing the modeled PcpB structure. After energy minimization of the complex, and successive minimizations of the system that consisted of the complex and the water layer surrounding the complex, the molecular dynamics of the system were simulated. The active-site residues of PcpB were identified on the basis of the modeled structure, and PcpB mutants were then designed to change the active site residues, expressed, and purified by affinity chromatography. The mutant activity was compared with that of the wild-type to investigate the validity of the modeled structure. The experimental results suggested that Phe85, Tyr216, and Arg235 were relevant to enzyme activity, and that Tyr397 and Phe87 were important for stabilization of the structure of PcpB.

Distribution of pentachlorophenol in phospholipid bilayers: a molecular dynamics study

Molecular dynamics computer simulations of pentachlorophenol (PCP) in palmitoyl-oleoyl-phosphatidylethanolamine and palmitoyl-oleoyl-phosphatidylcholine lipid bilayers were carried out to investigate the distribution of PCP and the effects of PCP on the phospholipid bilayer structure. Starting from two extreme starting structures, including PCP molecules outside the lipid bilayer, the PCP distribution converges in simulations of up to 50 ns. PCP preferentially occupies the region between the carbonyl groups and the double bonds in the acyl chains of the lipid molecules in the bilayer. In the presence of PCP, the lipid chain order increases somewhat in both chains, and the average tilt angle of the lipid chains decreases. The increase in the lipid chain order in the presence of PCP was more pronounced in the palmitoyl-oleoyl-phosphatidylcholine bilayer compared to the palmitoyl-oleoyl-phosphatidylethanolamine bilayer. The number of trans conformations of lipid chain dihedrals does not change significantly. PCP aligns parallel to the alkyl chains of the lipid to optimize the packing in the dense ordered chain region of the bilayer. The hydroxyl group of PCP forms hydrogen bonds with both water and lipid oxygen atoms in the water/lipid interface region.