5-chloromuconolactone and 2-chloromuconic-acid

2-Chloromuconate cycloisomerase from the Gram-positive bacterium Rhodococcus opacus 1CP (Rho-2-CMCI) is an enzyme of a modified ortho-pathway, in which 2-chlorophenol is degraded using 3-chlorocatechol as the central intermediate. In general, the chloromuconate cycloisomerases catalyze not only the cycloisomerization, but also the process of dehalogenation of the chloromuconate to dienelactone. However Rho-2-CMCI, unlike the homologous enzymes from the Gram-negative bacteria, is very specific for only one position of the chloride on the substrate chloromuconate. Furthermore, Rho-2-CMCI is not able to dehalogenate the 5-chloromuconolactone and therefore it cannot generate the dienelactone. The crystallographic structure of the homooctameric Rho-2-CMCI was solved by molecular replacement using the coordinates of the structure of chloromuconate cycloisomerase from Pseudomonas putida PRS2000. The structure was analyzed and compared to the other already known structures of (chloro)muconate cycloisomerases. In addition to this, molecular docking calculations were carried out, which allowed us to determine the residues responsible for the high substrate specificity and the lack of dehalogenation activity of Rho-2-CMCI. Our studies highlight that a histidine, located in a loop that closes the active site cavity upon the binding of the substrate, could be related to the dehalogenation inability of Rho-2-CMCI and in general of the muconate cycloisomerases.

Topics: 4-Butyrolactone; Adipates; Bacterial Proteins; Catalytic Domain; Catechols; Chlorophenols; Crystallography, X-Ray; Histidine; Intramolecular Lyases; Lactones; Molecular Docking Simulation; Protein Multimerization; Pseudomonas putida; Rhodococcus; Sorbic Acid; Structural Homology, Protein; Structure-Activity Relationship; Substrate Specificity

The 4-chloro- and 2,4-dichlorophenol-degrading strain Rhodococcus opacus 1CP has previously been shown to acquire, during prolonged adaptation, the ability to mineralize 2-chlorophenol. In addition, homogeneous chlorocatechol 1,2-dioxygenase from 2-chlorophenol-grown biomass has shown relatively high activity towards 3-chlorocatechol. Based on sequences of the N terminus and tryptic peptides of this enzyme, degenerate PCR primers were now designed and used for cloning of the respective gene from genomic DNA of strain 1CP. A 9.5-kb fragment containing nine open reading frames was obtained on pROP1. Besides other genes, a gene cluster consisting of four chlorocatechol catabolic genes was identified. As judged by sequence similarity and correspondence of predicted N termini with those of purified enzymes, the open reading frames correspond to genes for a second chlorocatechol 1,2-dioxygenase (ClcA2), a second chloromuconate cycloisomerase (ClcB2), a second dienelactone hydrolase (ClcD2), and a muconolactone isomerase-related enzyme (ClcF). All enzymes of this new cluster are only distantly related to the known chlorocatechol enzymes and appear to represent new evolutionary lines of these activities. UV overlay spectra as well as high-pressure liquid chromatography analyses confirmed that 2-chloro-cis,cis-muconate is transformed by ClcB2 to 5-chloromuconolactone, which during turnover by ClcF gives cis-dienelactone as the sole product. cis-Dienelactone was further hydrolyzed by ClcD2 to maleylacetate. ClcF, despite its sequence similarity to muconolactone isomerases, no longer showed muconolactone-isomerizing activity and thus represents an enzyme dedicated to its new function as a 5-chloromuconolactone dehalogenase. Thus, during 3-chlorocatechol degradation by R. opacus 1CP, dechlorination is catalyzed by a muconolactone isomerase-related enzyme rather than by a specialized chloromuconate cycloisomerase.

Topics: 4-Butyrolactone; Adipates; Amino Acid Sequence; Bacterial Proteins; Biodegradation, Environmental; Carbon-Carbon Double Bond Isomerases; Carboxylic Ester Hydrolases; Catechols; Cloning, Molecular; Dioxygenases; Hydrolases; Intramolecular Lyases; Molecular Sequence Data; Open Reading Frames; Oxygenases; Rhodococcus; Sequence Alignment; Sequence Analysis, DNA; Sorbic Acid

Muconate cycloisomerase (EC 5.5.1.1) and chloromuconate cycloisomerase (EC 5.5.1.7) were purified from extracts of Rhodococcus erythropolis 1CP cells grown with benzoate or 4-chlorophenol, respectively. Both enzymes discriminated between the two possible directions of 2-chloro-cis, cis-muconate cycloisomerization and converted this substrate to 5-chloromuconolactone as the only product. In contrast to chloromuconate cycloisomerases of gram-negative bacteria, the corresponding R. erythropolis enzyme is unable to catalyze elimination of chloride from (+)-5-chloromuconolactone. Moreover, in being unable to convert (+)-2-chloromuconolactone, the two cycloisomerases of R. erythropolis 1CP differ significantly from the known muconate and chloromuconate cycloisomerases of gram-negative strains. The catalytic properties indicate that efficient cycloisomerization of 3-chloro- and 2,4-dichloro-cis,cis-muconate might have evolved independently among gram-positive and gram-negative bacteria.

Topics: 4-Butyrolactone; Adipates; Amino Acid Sequence; Benzoates; Benzoic Acid; Biodegradation, Environmental; Chlorophenols; Intramolecular Lyases; Isomerases; Molecular Sequence Data; Rhodococcus; Sorbic Acid; Species Specificity; Substrate Specificity

2-Chloro-cis,cis-muconate, the product of ortho-cleavage of 3-chlorocatechol, was converted by purified preparations of the pJP4- and pAC27-encoded chloromuconate cycloisomerases (EC 5.5.1.7) to trans-dienelactone (trans-4-carboxymethylenebut-2-en-4-olide). The same compound was also formed when (+)-2-chloro- and (+)-5-chloromuconolactone were substrates of these enzyme preparations. Thus, the pJP4- and pAC27-encoded chloromuconate cycloisomerases are able to catalyze chloride elimination from (+)-5-chloromuconolactone. The ability to convert (+)-2-chloromuconolactone differentiates these enzymes from other groups of cycloisomerases.

Topics: 4-Butyrolactone; Acinetobacter; Adipates; Alcaligenes; Chromatography, High Pressure Liquid; Gram-Negative Aerobic Bacteria; Intramolecular Lyases; Isomerases; Sorbic Acid; Spectrophotometry

The conversion of 2-chloro-cis,cis-muconate by muconate cycloisomerase from Pseudomonas putida PRS2000 yielded two products which by nuclear magnetic resonance spectroscopy were identified as 2-chloro- and 5-chloromuconolactone. High-pressure liquid chromatography analyses showed the same compounds to be formed also by muconate cycloisomerases from Acinetobacter calcoaceticus ADP1 and Pseudomonas sp. strain B13. During 2-chloro-cis,cis-muconate turnover by the enzyme from P. putida, 2-chloromuconolactone initially was the major product. After prolonged incubation, however, 5-chloromuconolactone dominated in the resulting equilibrium. In contrast to previous assumptions, both chloromuconolactones were found to be stable at physiological pH. Since the chloromuconate cycloisomerases of Pseudomonas sp. strain B13 and Alcaligenes eutrophus JMP134 have been shown previously to produce the trans-dienelactone (trans-4-carboxymethylene-but-2-en-4-olide) from 2-chloro-cis,cis-muconate, they must have evolved the capability to cleave the carbon-chlorine bond during their divergence from normal muconate cycloisomerases.

Topics: 4-Butyrolactone; Acinetobacter calcoaceticus; Adipates; Intramolecular Lyases; Isomerases; Magnetic Resonance Spectroscopy; Pseudomonas; Pseudomonas putida; Sorbic Acid; Substrate Specificity