Structure, function, and post-translational regulation of the catalytic and modifier subunits of glutamate cysteine ligase

Abstract

Glutathione (GSH) is a tripeptide composed of glutamate, cysteine, and glycine. The first and rate-limiting step in GSH synthesis is catalyzed by glutamate cysteine ligase (GCL, previously known as γ-glutamylcysteine synthetase). GCL is a heterodimeric protein composed of catalytic (GCLC) and modifier (GCLM) subunits that are expressed from different genes. GCLC catalyzes a unique γ-carboxyl linkage from glutamate to cysteine and requires ATP and Mg++ as cofactors in this reaction. GCLM increases the Vmax and Kcat of GCLC, decreases the Km for glutamate and ATP, and increases the Ki for GSH-mediated feedback inhibition of GCL. While post-translational modifications of GCLC (e.g. phosphorylation, myristoylation, caspase-mediated cleavage) have modest effects on GCL activity, oxidative stress dramatically affects GCL holoenzyme formation and activity. Pyridine nucleotides can also modulate GCL activity in some species. Variability in GCL expression is associated with several disease phenotypes and transgenic mouse and rat models promise to be highly useful for investigating the relationships between GCL activity, GSH synthesis, and disease in humans.

Pyrroloquinoline quinone rescues hippocampal neurons from glutamate-induced cell death through activation of Nrf2 and up-regulation of antioxidant genes

“…HO-1 is a redox-sensitive inducible stress protein and plays a neuroprotective role against excitotoxicity damage and brain ischemia (Satoh et al, 2003), and cells from HO-1 -/-mice are highly susceptible to oxidative insults (Poss and Tonegawa, 1997). GCL, formerly known as γ-glutamylcysteine synthetase, is the rate-limiting enzyme in GSH biosynthesis, and comprises a catalytic subunit (GCLC) and a modulatory (GCLM) subunit (Griffith and Mulcahy, 1999;Franklin et al, 2009). Up-regulation of HO-1 and GCL expression through the ERK/Nrf2 pathway could protect hepatocytes against oxidative stress (Yang et al, 2011).…”

Activation of the Nuclear Factor E2-Related Factor 2/Antioxidant Response Element Pathway Is Neuroprotective after Spinal Cord Injury

“…Moreover, the relative levels of GCL subunits are a major determinant of cellular GCL activity and are highly regulated at the transcriptional and post-transcriptional level in response to oxidative stress. The GCL subunits are often coordinately induced in response to oxidative stress, but distinct transcriptional and post-transcriptional mechanisms mediate their differential rates and levels of induction (Franklin et al, 2009). In addition, NQO1 expression is also regulated at the post-transcriptional level (Tsvetkov et al, 2011).…”

Post-translational Activation of Glutamate Cysteine Ligase with Dimercaprol

“…The novelty of our approach lies with the finding of compounds that utilize a post-translational mechanism to increase GCL activity and intracellular GSH levels. This mechanism of action is unlikely to involve metal chelation, which would more likely inhibit rather than activate GCL based on the known requirement of Mg 2ϩ in the enzymatic activity of GCL (61).…”