Interactions of glutathione transferases with 4-hydroxynonenal

Abstract

Electrophilic products of lipid peroxidation are important contributors to the progression of several pathological states. The prototypical α,β-unsaturated aldehyde, 4-hydroxynonenal (HNE), triggers cellular events associated with oxidative stress, which can be curtailed by the glutathione-dependent elimination of HNE. The glutathione transferases (GSTs) are a major determinate of the intracellular concentration of HNE and can influence susceptibility to toxic effects, particularly when HNE and GST levels are altered in disease states. In this article, we provide a brief summary of the cellular effects of HNE, followed by a review of its GST-catalyzed detoxification, with an emphasis on the structural attributes that play an important role in the interactions with alpha-class GSTs. Some of the key determining characteristics that impart high alkenal activity reside in the unique C-terminal interactions of the GSTA4-4 enzyme. Studies encompassing both kinetic and structural analyses of related isoforms will be highlighted, with additional attention to stereochemical aspects that demonstrate the capacity of GSTA4-4 to detoxify both enantiomers of the biologically relevant racemic mixture while generating a select set of diastereomeric products with subsequent implications. A summary of the literature that examines the interplay between GSTs and HNE in model systems relevant to oxidative stress will also be discussed to demonstrate the magnitude of importance of GSTs in the overall detoxification scheme.

Figure 1

Reaction of GSH with racemic HNE. 1,4-addition reaction, followed by an intramolecular cyclization..

Figure 2

Comparison of the stereoselectivity of product formation for the different GST isoforms. The GSHNE diastereomers (gray line) were prepared by incubating GSH and (A) hGSTA4-4, (B) hGSTA1-1, and (C) hGSTP1-1 with racemic HNE and analyzed by LC/MS (electrospray positive ion mode, selected ion monitoring, m/z 464). The maximum contribution possible from the spontaneous reaction (black line), which produces small, roughly equivalent amounts of all four peaks, is also shown for comparison.

Figure 3

Comparison of key C-terminal domain interactions in alpha-class GSTs. Ribbon diagrams of a (A) hGSTA1-1 (PDB entry 1K3Y) and (B) hGSTA4-4 (PDB entry 1GUL) subunit as viewed perpendicular to the 2-fold axis of symmetry for the corresponding dimer. The tower region and α9-helix are emphasized in dark gray. The aromatic-aromatic interaction between F111 in the #4-turn-#5 tower region and Y217 in the #9-helix is depicted for hGSTA4-4. This interaction is not present in hGSTA1-1. The ligands are not shown for clarity.

Figure 4

Human GSTA4-4 active site. GSTA4-4 is shown in complex with 3S,4R-GSDHN (PDB entry 3IK7) as a model for the ternary complex formed with GSH and HNE. The 4-hydroxyl group is in proximity of R15, whereas the aldehyde-derived oxygen is near Y212 at the bottom of the H-site. The alkyl chain extends into the hydrophobic groove lined with other key active site residues shown as spheres.

Figure 5

HNE adduction of GSTA4-4. Ribbon diagram illustrating the location of the residues covalently modified by HNE within the context of the hGSTA4-4 subunit (PDB entry 1GUL). Identification of the adducted residues reveals that adduction does not occur in the H-site region. The view is aligned perpendicular to the 2-fold axis of symmetry for the corresponding dimer, with the tower region and the α9-helix emphasized in dark gray.