Metabolism of 2,2′- and 3,3′-Dihydroxybiphenyl by the Biphenyl Catabolic Pathway of Comamonas testosteroni B-356

Abstract

The purpose of this investigation was to examine the capacity of the biphenyl catabolic enzymes of Comamonas testosteroni B-356 to metabolize dihydroxybiphenyls symmetrically substituted on both rings. Data show that 3,3-dihydroxybiphenyl is by far the preferred substrate for strain B-356. However, the dihydrodiol metabolite is very unstable and readily tautomerizes to a dead-end metabolite or is dehydroxylated by elimination of water. The tautomerization route is the most prominent. Thus, a very small fraction of the substrate is converted to other hydroxylated and acidic metabolites. Although 2,2-dihydroxybiphenyl is a poor substrate for strain B-356 biphenyl dioxygenase, metabolites were produced by the biphenyl catabolic enzymes, leading to production of 2-hydroxybenzoic acid. Data show that the major route of metabolism involves, as a first step, a direct dehydroxylation of one of the ortho-substituted carbons to yield 2,3,2-trihydroxybiphenyl. However, other metabolites resulting from hydroxylation of carbons 5 and 6 of 2,2-dihydroxybiphenyl were also produced, leading to dead-end metabolites.The enzymes of the bacterial biphenyl catabolic pathway are very versatile. They can cometabolically transform several biphenyl analogs, including polychlorinated biphenyls (PCBs) (1, 31), hydroxybiphenyls, and chlorohydroxybiphenyls (33). The four enzymatic steps required to transform biphenyl or its analogs into corresponding benzoic acids are illustrated in Fig. 1. The initial reaction of this pathway is catalyzed by the biphenyl dioxygenase (BPDO) (13, 16). The cis-(2R,3S)-dihydroxy-1-phenylcyclohexa-4,6-diene(cis-biphenyl-2,3-dihydrodiol) (commonly called cis-2,3-dihydro-2,3-dihydroxybiphenyl) generated by the catalytic oxygenation of biphenyl is dehydrogenated by the 2,3-dihydro-2,3-dihydroxybiphenyl 2,3-dehydrogenase (BphB), and the catechol produced is cleaved by the 2,3-dihydroxybiphenyl 1,2-dioxygenase. The 2-hydroxy-6-oxo-6-phenylhexa-2,4-dienoic acid (HOPDA) is then hydrolyzed by the HOPDA hydrolase to yield benzoate and hydroxypentanoate. The substrate specificity of BPDO is crucial, because it limits the range of compounds potentially degradable by the catabolic system (14).For example, the three symmetrical ortho, meta, or parasubstituted dichlorinated biphenyl isomers are not metabolized equally well by various BPDOs. Comamonas testosteroni strain B-356 BPDO oxygenates 3,3Ј-dichlorobiphenyl much faster and more efficiently than 2,2Ј-dichlorobiphenyl and 4,4Ј-dichlorobiphenyl. On the other hand, the catalytic activity of Burkholderia sp. strain LB400 BPDO toward 2,2Ј-dichlorobiphenyl is much more efficient than that of B-356 BPDO (17), but 3,3Ј-dichlorobiphenyl and 4,4Ј-dichlorobiphenyl are poor substrates for LB400 BPDO. Nevertheless, metabolites generated from B-356 and LB400 demonstrating BPDO attack on each of these three substrates have been detected and identified (2, 14, 17). It is noteworthy that, for both strains, BPDO attacks 2,2Ј-dichlorobiphenyl principally at position 2,3, which results in...

Revisiting the Regiospecificity of Burkholderia xenovorans LB400 Biphenyl Dioxygenase toward 2,2′-Dichlorobiphenyl and 2,3,2′,3′-Tetrachlorobiphenyl

“…For example, 3,3Ј-dihydroxybiphenyl is converted to an unstable dihydrodiol metabolite that readily isomerizes to 3,4-dihydroxy-5-(3Ј-hydroxyphenyl)-5-cyclohexen-1-one, which is a dead-end metabolite (18). Several hydroxychlorobiphenyls were also found to generate unstable dihydrodiol metabolites (19).…”

Oxidative biotransformations of phenol substrates catalysed by toluene dioxygenase: A molecular docking study

“…[1][2][3][4][5][6][7][8][9][10][11][12][13][14]. Thus, toluene dioxygenase (TDO) [2,3,[7][8][9][10][11], naphthalene dioxygenase (NDO) [9,12], biphenyl dioxygenase (BPDO) [9,12,13] and o-xylene dioxygenase (OXDO) [14] have all been used to catalyse the formation of catechols B, as major metabolites of phenols A. To date, the binding interactions of phenolic substrates with amino acid residues at the active site of RHDs are relatively unexplored.…”

“…Recent reports showed that, in many cases, catechols B were accompanied by a new family of cyclohex-2-en-1-one cis-diols, as major metabolites (F and G) [7][8][9][10][11]13]. Biotransformations of phenols, with the TDO-expressing constitutive mutant Pseudomonas putida UV4 and recombinant strain Escherichia coli p-CL-4t, resulted in more than twenty cyclohex-2-en-1-one cis-diols (F and G) being added to this new family of metabolites [7][8][9][10][11].…”

“…TDO-catalysed hydroxylation mechanisms have been postulated to account for: (a) the formation of benzene-1,2-diols (catechols, D) via triol intermediates (C) [3], (b) benzene-1,4-diols (hydroquinones, E) [11,14] and (c) cyclohex-2-en-1-one cis-diols (F and G) via cis-dihydrodiol metabolites (B and H) [7][8][9][10][11]13] (Scheme 1). While the dehydration of cyclohex-2-en-1-onecis-diols F and G, to yield hydroquinones E, was observed in the presence of acid and occurred during biotransformations, neither triol C nor cisdihydrodiol intermediates B and H were detected.…”

Metabolism of Doubly para -Substituted Hydroxychlorobiphenyls by Bacterial Biphenyl Dioxygenases

“…The pathway used by aerobic bacteria to degrade biphenyl is also used to metabolize or cometabolize several hydroxy-and hydroxychlorobiphenyls with an initial attack by the biphenyl dioxygenase (BPDO) (9). However, the profile of the metabolites generated by this pathway has been determined for only a few of these biphenyl analogs (8,10,11). The metabolism of an ortho-hydroxylated biphenyl by a monooxygenase has also been reported.…”