The C-Terminal Region of Human Glutathione Transferase A1-1 Affects the Rate of Glutathione Binding and the Ionization of the Active-Site Tyr9†

Contamination of drinking water with toxic inorganic arsenic is a major public health issue. The mechanisms of enzymes and transporters in arsenic elimination are therefore of interest. The human omega-class glutathione transferases have been previously shown to possess monomethylarsonate (V) reductase activity. To further understanding of this activity, molecular dynamics of human GSTO1-1 bound to glutathione with a monomethylarsonate isostere were simulated to reveal putative monomethylarsonate binding sites on the enzyme. The major binding site is in the active site, adjacent to the glutathione binding site. Based on this and previously reported biochemical data, a reaction mechanism for this enzyme is proposed. Further insights were gained from comparison of the human omega-class GSTs to homologs from a range of animals.

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Active-site tyrosyl residues are targets in the irreversible inhibition of a class Mu glutathione transferase by 2-(S-glutathionyl)-3,5,6-trichloro-1,4-benzoquinone.

Journal of Biological Chemistry ◽

10.1016/s0021-9258(18)47103-7 ◽

1994 ◽

Vol 269 (43) ◽

pp. 26890-26897

Author(s):

J H Ploemen ◽

W W Johnson ◽

S Jespersen ◽

D Vanderwall ◽

B van Ommen ◽

...

Keyword(s):

Active Site ◽

Glutathione Transferase ◽

Irreversible Inhibition

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Aromatic residues in the C-terminal region of glutathione transferase A1-1 influence rate-determining steps in the catalytic mechanism [Biochimica et Biophysica Acta 1597 (2002) 157-163]

Biochimica et Biophysica Acta (BBA) - Proteins and Proteomics ◽

10.1016/s0167-4838(02)00362-x ◽

2002 ◽

Vol 1598 (1-2) ◽

pp. 199-205 ◽

Cited By ~ 8

Author(s):

Lisa O. Nilsson ◽

Maryam Edalat ◽

Pär L. Pettersson ◽

Bengt Mannervik

Keyword(s):

Catalytic Mechanism ◽

Glutathione Transferase ◽

Terminal Region ◽

Aromatic Residues ◽

Rate Determining Steps

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The Role of Glutathione in the Isomerization of Δ5-Androstene- 3,17-dione Catalyzed by Human Glutathione Transferase A1-1

Journal of Biological Chemistry ◽

10.1074/jbc.m009146200 ◽

2001 ◽

Vol 276 (15) ◽

pp. 11698-11704 ◽

Cited By ~ 37

Author(s):

Pär L. Pettersson ◽

Bengt Mannervik

Keyword(s):

Active Site ◽

Active Sites ◽

Catalytic Mechanism ◽

Glutathione Transferase ◽

Ph Dependence ◽

Enzymatic Catalysis ◽

Catalytic Efficiency ◽

Protonated Form ◽

Hydroxyl Group ◽

Isomerization Reaction

Human glutathione transferase (GST) A1-1 efficiently catalyzes the isomerization of Δ5-androstene-3,17-dione (AD) into Δ4-androstene-3,17-dione. High activity requires glutathione, but enzymatic catalysis occurs also in the absence of this cofactor. Glutathione alone shows a limited catalytic effect.S-Alkylglutathione derivatives do not promote the reaction, and the pH dependence of the isomerization indicates that the glutathione thiolate serves as a base in the catalytic mechanism. Mutation of the active-site Tyr9into Phe significantly decreases the steady-state kinetic parameters, alters their pH dependence, and increases the pKavalue of the enzyme-bound glutathione thiol. Thus, Tyr9promotes the reaction via its phenolic hydroxyl group in protonated form. GST A2-2 has a catalytic efficiency with AD 100-fold lower than the homologous GST A1-1. Another Alpha class enzyme, GST A4-4, is 1000-fold less active than GST A1-1. The Y9F mutant of GST A1-1 is more efficient than GST A2-2 and GST A4-4, both having a glutathione cofactor and an active-site Tyr9residue. The active sites of GST A2-2 and GST A1-1 differ by only four amino acid residues, suggesting that proper orientation of AD in relation to the thiolate of glutathione is crucial for high catalytic efficiency in the isomerization reaction. The GST A1-1-catalyzed steroid isomerization provides a complement to the previously described isomerase activity of 3β-hydroxysteroid dehydrogenase.

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