Structure-activity relationships of 4-hydroxyalkenals in the conjugation catalysed by mammalian glutathione transferases

Abstract

The substrate specificities of 15 cytosolic glutathione transferases from rat, mouse and man have been explored by use of a homologous series of 4-hydroxyalkenals, extending from 4-hydroxypentenal to 4-hydroxypentadecenal. Rat glutathione transferase 8-8 is exceptionally active with the whole range of 4-hydroxyalkenals, from C5 to C15. Rat transferase 1-1, although more than 10-fold less efficient than transferase 8-8, is the second most active transferase with the longest chain length substrates. Other enzyme forms showing high activities with these substrates are rat transferase 4-4 and human transferase mu. The specificity constants, kcat./Km, for the various enzymes have been determined with the 4-hydroxyalkenals. From these constants the incremental Gibbs free energy of binding to the enzyme has been calculated for the homologous substrates. The enzymes responded differently to changes in the length of the hydrocarbon side chain and could be divided into three groups. All glutathione transferases displayed increased binding energy in response to increased hydrophobicity of the substrate. For some of the enzymes, steric limitations of the active site appear to counteract the increase in binding strength afforded by increased chain length of the substrate. Comparison of the activities with 4-hydroxyalkenals and other activated alkenes provides information about the active-site properties of certain glutathione transferases. The results show that the ensemble of glutathione transferases in a given species may serve an important physiological role in the conjugation of the whole range of 4-hydroxyalkenals. In view of its high catalytic efficiency with all the homologues, rat glutathione transferase 8-8 appears to have evolved specifically to serve in the detoxication of these reactive compounds of oxidative metabolism.

X‐ray crystal structures of cytosolic glutathione S‐transferases

“…Furthermore, since substrate recognition at the H-site is mediated primarily by hydrophobic interactions, binding at this site is expected, within the steric limitations of each gene class H-site, to be less constrained, thus giving it the flexibility required to accommodate a range of structurally different hydrophobic substrates. Structure/activity investigations, exploring the significance of hydrophobic interactions at the H-site, indicate that cytosolic glutathione S-transferases generally exhibit increased binding affinities in response to increased hydrophobicity of 4-hydroxyalkenal substrates [116] and of the alkyl group in S-alkylated glutathione competitive inhibitors [117].…”

Lipid Peroxidation Products and Antioxidants in Human Disease

“…However, the reported ability of HNE to modify proteins and therefore influence enzymatic activity, led us to study the possibility of a direct interaction between HNE and GSHPx. HNE reacts with GSH spontaneously, but within cells this reaction proceeds at a much higher rate, catalyzed by specific isoforms of GSH S-transferases (66,67). Moreover, reaction of this aldehyde with other aminoacid residues leads to the modification of proteins and eventually to the inactivation of their enzymatic activity.…”

Glutathione S‐Transferase 8‐8 Expression Is Lower in Alcohol‐Preferring Than in Alcohol‐Nonpreferring Rats

“…The function of rGST 8-8 has not been elucidated in the brain regions where we have detected differential expression, and these brain regions are known to be important in the brain reward pathway. Because GSTs are multifunctional proteins that are involved in transport and biosynthesis of endogenous compounds and play a defensive role against oxidative damage as well as neuroprotection (Danielson et al, 1987;Hubatsch et al, 1998;Singhal et al, 1994), they could be playing a role in these rat brain regions that has yet to be discovered. It has been shown that alcohol exposure alters the glutathione/glutathione transferase (Schnellmann et al, 1984) and the glutathione/glutathione peroxidase-1 systems (Bailey et al, 2001) in response to ethanol-related oxidative stress.…”

“…Author Manuscript (Bjornestedt et al, 1995;Danielson et al, 1987). Because the GST 8-8 designation is widely used in the literature, this nomenclature is used throughout this article.…”

“…GST isoenzymes have been categorized into eight classes: GSTA, GSTM, GSTP, GSTS, GSTT, GSTZ, GSTK, and GSTO (Board et al, 1997(Board et al, , 2000Meyer et al, 1991;Hayes and Pulford, 1995;Pemble et al, 1996). rGST 8-8, a class α isoenzyme that has recently been designated rGSTA4 (Hayes and Pulford, 1995;Meyer et al, 1989;Stenberg et al, 1992), has special catalytic specificity toward 4-hydroxyalkenal and acrolein (Bjornestedt et al, 1995;Danielson et al, 1987). Because the GST 8-8 designation is widely used in the literature, this nomenclature is used throughout this article.…”