Involvement of PEG-carboxylate dehydrogenase and glutathione S-transferase in PEG metabolism by Sphingopyxis macrogoltabida strain 103

Abstract

Sphingopyxis terrae and the Sphingopyxis macrogoltabida strains 103 and 203 are able to degrade polyethylene glycol (PEG). They possess the peg operon, which is responsible for the conversion of PEG to PEG-carboxylate-coenzyme A (CoA). The upstream (3.0 kb) and downstream (6.5 kb) regions of the operon in strain 103 were cloned and sequenced. The structure was well conserved between S. macrogoltabida strain 203 and S. terrae, except that two sets of transposases are absent in strain 203. The downstream region contains the genes for PEG-carboxylate dehydrogenase (PCDH), glutathione S-transferase (GST), tautomerase, and a hypothetical protein. The genes for pcdh and gst were transcribed constitutively and monocistronically, indicating that their transcription is independent of the operon regulation. PCDH and GST were expressed in Escherichia coli and characterized biochemically. PCDH is a homotetramer of 64-kDa subunits and contains one molecule of flavin adenine dinucleotide per subunit. The enzyme dehydrogenates PEG-carboxylate to yield glyoxylate, suggesting that the enzyme is the third enzyme involved in PEG degradation. GST is a homodimer of 28-kDa subunits. GST activity was noncompetitively inhibited by acyl-CoA and PEG-carboxylate-CoA, suggesting the interaction of GST with them. The proposed role for GST is to buffer the toxicity of PEG-carboxylate-CoA.

The Biochemistry and Molecular Biology of Xenobiotic Polymer Degradation by Microorganisms

“…28) Judging from the nature of this kind of protein (located on the cytoplasmic membrane as a translocator), the enzyme might be responsible for the translocation of PEG-carboxylate from the periplasm into the cytoplasm or for the detoxification of strong acidity of the substrate. Since glutathione S-transferase (a gene coding this enzyme is located in the downstream of the peg operon) is localized in the cytoplasm and suggested to buffer the toxicity of PEG-carboxylateCoA, 29) the role of acyl-CoA synthetase might be to buffer the toxicity of PEG-carboxylate (perhaps a low molecular size) together with glutathione S-transferase. Other two genes code proteins related to transport, TonB-dependent receptor and permease respectively.…”

“…30,31) A gene coding PEG-carboxylate dehydrogenase was detected in the downstream region of the peg operon, and was found to be involved in PEG metabolism. 29) In addition, superoxide dismutase cloned from PEG-utilizing Pseudonocardia sp. strain K1 showed ether-bond-cleaving activity for carboxylated PEG.…”

Degradation of Recalcitrant Polyurethane and Xenobiotic Additives by a Selected Landfill Microbial Community and Its Biodegradative Potential Revealed by Proximity Ligation-Based Metagenomic Analysis

“…superoxide dismutase (RQP04715.1, RQP13424.1, RQP09887.1, RQP11889.1, RQP18047.1, RQP18034.1, RQP09190.1, RQP20377.1), as well as genes encoding enzymes involved in glutathione metabolism, which have been proposed to participate in PEG metabolism (Somyoonsap et al, 2008) were identified ( Figure 7B and Table 3).…”

“…Besides, the pathways for glyoxylate, butanoate, pyruvate and formate metabolisms as well as the TCA pathway were fully reconstructed from the BP8 metagenome ( Figure 7B). Additionally, in PEG metabolism, long chains of PEG-carboxylate can be processed by acyl-CoA synthetase and glutathione-S transferase forming glutathioneconjugates (Somyoonsap et al, 2008). Although these reactions would not be needed for glycol ethers catabolism, they could be required for the degradation of long PPG moieties that are part of the PE-PU-A copolymer ( Figure 3A).…”

Characterization of a Cryptic Plasmid, pSM103mini, from Polyethylene-Glycol DegradingSphingopyxis macrogoltabidaStrain 103

“…S. terrae and Sphingopyxis macrogoltabida strains 103 and 203 can degrade polyethylene glycol (PEG), a compound utilized and released by mankind in the last 40 years. 2) They have well-conserved PEG-degradative genes coordinated as an operon, 3) containing PEG-degradative genes [4][5][6] and transcriptional regulators for the operon.…”