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Structural insight into glucose‐6‐phosphate dehydrogenase (G6PD) deficiency – Discovery of novel G6PD activators to correct G6PD deficiency
Author(s) -
HWANG SUNHEE
Publication year - 2016
Publication title -
the faseb journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.709
H-Index - 277
eISSN - 1530-6860
pISSN - 0892-6638
DOI - 10.1096/fasebj.30.1_supplement.612.7
Subject(s) - pentose phosphate pathway , oxidative stress , glucose 6 phosphate dehydrogenase deficiency , nicotinamide adenine dinucleotide phosphate , glucose 6 phosphate dehydrogenase , heinz body , glutathione , antioxidant , biochemistry , dehydrogenase , oxidative phosphorylation , chemistry , biology , enzyme , glycolysis , hemoglobin , oxidase test
The cells in our body have several mechanisms to counteract oxidative stress by producing antioxidants. One of the natural sources of antioxidants occurs through the activity of an enzyme known as glucose‐6‐phosphate dehydrogenase (G6PD). G6PD catalyzes the first and rate‐limiting step of the pentose phosphate pathway, in which reduced NADPH (nicotinamide adenine dinucleotide phosphate) is generated. NADPH is in turn used to maintain the supply of reduced glutathione (GSH), which plays a critical role in regulating antioxidant balance and thus protecting cells from oxidative damage in general. Particularly, erythrocytes, which lack mitochondria, have no other means of generating NADPH in other pathways and rely solely on G6PD for the generation of antioxidants. However, G6PD deficiency, caused by a loss of enzymatic activity and structural integrity due to a variety of different mutations of the G6PD gene, disrupts the physiological antioxidant balance with significant decreases in NADPH and GSH levels and thus increases the vulnerability to oxidative stress in cells. Lacking protection against oxidative stress, G6PD‐deficient individuals are highly susceptible to hemolytic anemia, neonatal jaundice (caused by a higher level of bilirubin in the blood), and they further develop other severe diseases such as kernicterus (bilirubin‐induced brain damage). Currently there are no treatments available for G6PD deficiency. Given that G6PD deficiency can lead to such devastating diseases and may contribute to increased sensitivity to other oxidative stress, there is a pressing need to develop a therapeutic plan that will correct G6PD deficiency. Towards this end, we first characterized one of the most common G6PD mutant enzymes, Canton G6PD, by X‐ray crystallography, which through we identified the structurally distorted areas in the enzyme leading to the decreased enzyme activity. Using this mutant enzyme, we screened over 100,000 molecules for activators and identified a potential molecule that activated the enzyme by at least 2‐fold. This molecule promoted dimerization of the enzyme, which is necessary for enzyme activity, and prevented proteolysis by increasing the stability of the enzyme as well. Furthermore, this molecule activated three other common G6PD mutant enzymes, suggesting that it facilitates either cofactor (NADP + ) or substrate binding to the enzyme. In cells under oxidative stress, the molecule increased the production of both NADPH and GSH, indicating that it enhances cells’ reducing power to combat oxidative stress. Currently, we are determining the crystal structure of Canton G6PD in complex with the lead molecule and conducting structure‐and‐relationship (SAR) studies for lead optimization. Taken together, our study characterize the effect of the small molecule for G6PD deficiency for the first time, and this will be a first step in a drug discovery effort to correct G6PD deficiency and treat diseases associated with the deficiency. 1Overlaid crystal structures of wild‐type G6PD (in blue) and Canton G6PD (R459L in orange): A loose helical interaction around Canton mutation leads to the decreased enzymatic activity of Canton G6PD