Roles of the enantioselective glutathione S-transferases in cleavage of beta-aryl ether.
Cleavage of the beta-aryl ether linkage is the most important process in lignin degradation. Here we characterize the three tandemly located glutathione S-transferase (GST) genes, ligF, ligE, and ligG, from low-molecular-weight lignin-degrading Sphingomonas paucimobilis SYK-6, and we describe the actual roles of these genes in the beta-aryl ether cleavage. Based on the identification of the reaction product by electrospray ionization-mass spectrometry, a model compound of beta-aryl ether, alpha-(2-methoxyphenoxy)-beta-hydroxypropiovanillone (MPHPV), was transformed by LigF or LigE to guaiacol and alpha-glutathionyl-beta-hydroxypropiovanillone (GS-HPV). This result suggested that LigF and LigE catalyze the nucleophilic attack of glutathione on the carbon atom at the beta position of MPHPV. High-pressure liquid chromatography-circular dichroism analysis indicated that LigF and LigE each attacked a different enantiomer of the racemic MPHPV preparation. The ligG gene product specifically catalyzed the elimination of glutathione from GS-HPV generated by the action of LigF. This reaction then produces an achiral compound, beta-hydroxypropiovanillone, which is further degraded by this strain. Disruption of the ligF, ligE, and ligG genes in SYK-6 showed that ligF is essential to the degradation of one of the MPHPV enantiomers, and the alternative activities which metabolize the substrates of LigE and LigG are present in this strain.
Masai
Eiji
E
Department of Bioengineering, Nagaoka University of Technology, Nagaoka, Niigata 940-2188, Japan. emasai@vos.nagaokaut.ac.jp
Ichimura
Atsushi
A
Sato
Yusuke
Y
Miyauchi
Keisuke
K
Katayama
Yoshihiro
Y
Fukuda
Masao
M
D001426:Bacterial Proteins; D002851:Chromatography, High Pressure Liquid; D002942:Circular Dichroism; D004987:Ethers / Q000737:chemistry* / Q000378:metabolism; D017353:Gene Deletion; D015964:Gene Expression Regulation, Bacterial; D005978:Glutathione / Q000378:metabolism; D005982:Glutathione Transferase / Q000235:genetics / Q000378:metabolism*; D008031:Lignin / Q000737:chemistry / Q000378:metabolism*; D008190:Lyases / Q000235:genetics / Q000378:metabolism; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism*; D021241:Spectrometry, Mass, Electrospray Ionization; D020578:Sphingomonas / Q000201:enzymology* / Q000235:genetics; D013237:Stereoisomerism
D001426:Bacterial Proteins; D004987:Ethers; D008031:Lignin; D010088:Oxidoreductases; C060093:aryl ether cleaving enzyme; D005982:Glutathione Transferase; D008190:Lyases; D005978:Glutathione