Mutant/mutation
The mutant contains an additional copy of the gene encoding gamma-glutamylcysteine synthetase (γ-GCS). This gene is under control of the constitutive eef1a promoter and is introduced into the silent c/d-rRNA genomic locus

Protein (function)
γ-GCS catalyzes the rate limiting step during GSH biosynthesis. GSH is a thiol-based tripeptide implicated in a variety of cellular processes, including detoxification of xenobiotics and protection against reactive oxygen species

In most eukaryotic organisms, redox-active enzymes, such as catalase, superoxide dismutase, and peroxidases as well as an enzymatic cascade that generates reduced electron donors, i.e. glutathione (GSH) and thioredoxin (Trx), sustain the cellular redox homeostasis. This redox network is split into two major arms, the GSH and the Trx system, that serve complementary functions in antioxidant defense and DNA synthesis. The malarial parasite Plasmodium lacks two central antioxidant enzymes: (i) catalase that typically detoxifies hydrogen peroxide and (ii) a classical glutathione peroxidase, a selenoenyzme that reduces lipid hydroperoxides to their alcohols. This apparent deficiency raises doubts about the relevance of the glutathione (GSH) pathway in detoxification of oxidative stress in Plasmodium. However, supportive of a role for GSH metabolism in the detoxification process are the observations that the P. falciparum glutathione S-tranferase enzyme, which conjugates GSH to other molecules via the sulfhydryl group, displays peroxidase activity.

Evidence has been presented that P. falciparum does not utilize GSH from the host red blood cell since the parasite membrane is neither permeable to host GSH nor γ-glutamylcysteine. Plasmodium is therefore thought to be dependent on its own GSH biosynthetic pathway. GSH is synthesized in Plasmodium by consecutive reactions facilitated by the enzymes γ-glutamylcysteine synthetase (γ-GCS) and glutathione synthetase (GS). However, it has been hypothesized that host GSH can be transported into the P. berghei food vacuole via hemoglobin-containing endocytic vesicles, based on data showing that GSH can detoxify the toxic ferriprotoporphyrin IX inside the parasite's food vacuole.

See mutants RMgm-204 and RMgm-1407 for mutants lacking expression of γ-GCS. These mutants show a reduced growth rate.

See also mutants RMgm-403 and RMgm-404 that lack expression of glutathione reductase (GR). Phenotype analyses of these mutants indicate that similar to what was reported for γ-GCS, GR is not essential for parasite blood stage development but it does play a critical role during oocyst development in the mosquito

Phenotype
See Additional information

Additional information
Analyses are presented on the drug-sensitivity of mutants lacking (RMgm-204) and over-expressing γ-GCS (see for such studies also mutant RMgm-1417).

Evidence is presented that mutants lacking γ-GCS have increased sensitivity to artemisinin

Overexpression of pbggcs mRNA in blood stages of the pbggcs-oe parasites was demonstrated by RNase Protection Assay. The pbggcs mRNA levels in pbggcs-oe1 and pbggcs-oe2 parasites were 5.3 (P<0.001) and 4.3 (P<0.01) times higher respectively relative to wild type parasites.
To investigate whether or not overexpression of the pbggcs gene results in increased parasite GSH levels, total GSH was determined in pbggcs-oe and wild type parasites by HPLC. Total GSH levels were significantly higher in pbggcs-oe1 (17.5 nmol/10⁹ parasites, SD ±15.2, P<0.05) and pbggcs-oe2 (22.3 nmol/10⁹ parasites, SD ±19.3, P<0.001) parasites when compared to wild type (7.4 nmol/10⁹ parasites, SD ±1.7)

Other mutants
See  RMgm-204 and RMgm-1417 for mutants lacking expression of γ-GCS.
RMgm-1418: A mutant over-expressing γ-GCS
RMgm-403, RMgm-404: Mutants lacking expression of glutathione reductase (GR).