Novel folding and stability defects cause a deficiency of human glutathione transferase omega 1.
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Zhou H, Brock J, Casarotto MG, Oakley AJ, Board PG
Novel folding and stability defects cause a deficiency of human glutathione transferase omega 1.
J Biol Chem. 2011 Feb 11;286(6):4271-9. doi: 10.1074/jbc.M110.197822. Epub 2010 Nov 24.
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21106529 [View in PubMed]
- Abstract
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The polymorphic deletion of Glu-155 from human glutathione transferase omega1 (GSTO1-1) occurs in most populations. Although the recombinant DeltaGlu-155 enzyme expressed in Escherichia coli is active, the deletion causes a deficiency of the active enzyme in vivo. The crystal structure and the folding/unfolding kinetics of the DeltaGlu-155 variant were determined in order to investigate the cause of the rapid loss of the enzyme in human cells. The crystal structure revealed altered packing around the Glu-155 deletion, an increase in the predicted solvent-accessible area and a corresponding reduction in the buried surface area. This increase in solvent accessibility was consistent with an elevated Stern-Volmer constant. The unfolding of both the wild type and DeltaGlu-155 enzyme in urea is best described by a three-state model, and there is evidence for the more pronounced population of an intermediate state by the DeltaGlu-155 enzymes. Studies using intrinsic fluorescence revealed a free energy change around 14.4 kcal/mol for the wild type compared with around 8.6 kcal/mol for the DeltaGlu-155 variant, which indicates a decrease in stability associated with the Glu-155 deletion. Urea induced unfolding of the wild type GSTO1-1 was reversible through an initial fast phase followed by a second slow phase. In contrast, the DeltaGlu-155 variant lacks the slow phase, indicating a refolding defect. It is possible that in some conditions in vivo, the increased solvent-accessible area and the low stability of the DeltaGlu-155 variant may promote its unfolding, whereas the refolding defect limits its refolding, resulting in GSTO1-1 deficiency.