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| [[Image:1c72.gif|left|200px]] | | {{Seed}} |
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| {{STRUCTURE_1c72| PDB=1c72 | SCENE= }} | | {{STRUCTURE_1c72| PDB=1c72 | SCENE= }} |
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| '''TYR115, GLN165 AND TRP209 CONTRIBUTE TO THE 1,2-EPOXY-3-(P-NITROPHENOXY)PROPANE CONJUGATING ACTIVITIES OF GLUTATHIONE S-TRANSFERASE CGSTM1-1'''
| | ===TYR115, GLN165 AND TRP209 CONTRIBUTE TO THE 1,2-EPOXY-3-(P-NITROPHENOXY)PROPANE CONJUGATING ACTIVITIES OF GLUTATHIONE S-TRANSFERASE CGSTM1-1=== |
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| ==Overview==
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| We investigated the epoxidase activity of a class mu glutathione S-transferase (cGSTM1-1), using 1,2-epoxy-3-(p-nitrophenoxy)propane (EPNP) as substrate. Trp209 on the C-terminal tail, Arg107 on the alpha4 helix, Asp161 and Gln165 on the alpha6 helix of cGSTM1-1 were selected for mutagenesis and kinetic studies. A hydrophobic side-chain at residue 209 is needed for the epoxidase activity of cGSTM1-1. Replacing Trp209 with histidine, isoleucine or proline resulted in a fivefold to 28-fold decrease in the k(cat)(app) of the enzyme, while a modest 25 % decrease in the k(cat)(app) was observed for the W209F mutant. The rGSTM1-1 enzyme has serine at the correponding position. The k(cat)(app) of the S209W mutant is 2. 5-fold higher than that of the wild-type rGSTM1-1. A charged residue is needed at position 107 of cGSTM1-1. The K(m)(app)(GSH) of the R107L mutant is 38-fold lower than that of the wild-type enzyme. On the contrary, the R107E mutant has a K(m)(app)(GSH) and a k(cat)(app) that are 11-fold and 35 % lower than those of the wild-type cGSTM1-1. The substitutions of Gln165 with Glu or Leu have minimal effect on the affinity of the mutants towards GSH or EPNP. However, a discernible reduction in k(cat)(app) was observed. Asp161 is involved in maintaining the structural integrity of the enzyme. The K(m)(app)(GSH) of the D161L mutant is 616-fold higher than that of the wild-type enzyme. In the hydrogen/deuterium exchange experiments, this mutant has the highest level of deuteration among all the proteins tested.We also elucidated the structure of cGSTM1-1 co-crystallized with the glutathionyl-conjugated 1, 2-epoxy-3-(p-nitrophenoxy)propane (EPNP) at 2.8 A resolution. The product found in the active site was 1-hydroxy-2-(S-glutathionyl)-3-(p-nitrophenoxy)propane, instead of the conventional 2-hydroxy isomer. The EPNP moiety orients towards Arg107 and Gln165 in dimer AB, and protrudes into a hydrophobic region formed by the loop connecting beta1 and alpha1 and part of the C-terminal tail in dimer CD. The phenoxyl ring forms strong ring stacking with the Trp209 side-chain in dimer CD. We hypothesize that these two conformations represent the EPNP moiety close to the initial and final stages of the reaction mechanism, respectively.
| | The line below this paragraph, {{ABSTRACT_PUBMED_10903867}}, adds the Publication Abstract to the page |
| | (as it appears on PubMed at http://www.pubmed.gov), where 10903867 is the PubMed ID number. |
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| | {{ABSTRACT_PUBMED_10903867}} |
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| ==About this Structure== | | ==About this Structure== |
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| [[Category: Steady-state kinetic]] | | [[Category: Steady-state kinetic]] |
| [[Category: X-ray crystallography]] | | [[Category: X-ray crystallography]] |
| ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Fri May 2 12:24:23 2008'' | | |
| | ''Page seeded by [http://oca.weizmann.ac.il/oca OCA ] on Mon Jun 30 20:18:19 2008'' |
