Human glutathione transferase zeta.
Zeta-class glutathione transferases (GSTZs) were recently discovered by a bioinformatics approach and the availability of human expressed sequence tag databases. Although GSTZ showed little activity with conventional GST substrates (1-chloro-2,4-dinitrobenzene; organic hydroperoxides), GSTZ was found to catalyze the oxygenation of dichloroacetic acid (DCA) to glyoxylic acid and the cis-trans isomerization of maleylacetoacetate to fumarylacetoacetate. Hence, GSTZ plays a critical role in the tyrosine degradation pathway and in alpha-haloacid metabolism. The GSTZ-catalyzed biotransformation of DCA is of particular interest, because DCA is used in the human clinical management of congenital lactic acidosis and because DCA is a common drinking water contaminant. Substrate selectivity studies showed that GSTZ catalyzes the glutathione-dependent biotransformation of a range of dihaloacetic acids along with fluoroacetic acid, 2-halopropanoic acids, and 2,2-dichloropropanoic acid. Human clinical studies showed that the elimination half-life of DCA increases with repeated doses of DCA; also, rats given DCA show low GSTZ activity with DCA as the substrate. DCA was found to be a mechanism-based inactivator of GSTZ, and proteomic studies showed that Cys-16 of human GSTZ1-1 is covalently modified by a reactive intermediate that contains glutathione and the carbon skeleton of DCA. Bioinformatics studies also showed the presence of at least four polymorphic variants of human GSTZ; these variants differ considerably in the rates of catalysis and in their susceptibility to inactivation by DCA. Finally, Gstz1(-/-) mouse strains have been developed; these mice fail to biotransform DCA or maleylacetone. Although the mice have no obvious phenotype, a high incidence of lethality is observed in young mice given phenylalanine in their drinking water. Gstz1(-/-) mice should prove useful in expanding the role of GSTZ in alpha-haloacid metabolism and in the tyrosine degradation pathway.
Board
Philip G
PG
Molecular Genetics Group, John Curtin School of Medical Research, Australian National University, CAnaberra, Australia.
Anders
M W
MW
D000143:Acids / Q000737:chemistry / Q000378:metabolism; D000818:Animals; D001711:Biotransformation; D005982:Glutathione Transferase / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006239:Haplotypes; D006801:Humans; D006846:Hydrocarbons, Halogenated / Q000737:chemistry / Q000378:metabolism; D007527:Isoenzymes / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D015394:Molecular Structure; D011110:Polymorphism, Genetic; D013379:Substrate Specificity
D000143:Acids; D006846:Hydrocarbons, Halogenated; D007527:Isoenzymes; C407705:GSTZ1 protein, human; D005982:Glutathione Transferase