A novel missense mutation in the γ-glutamylcysteine synthetase catalytic subunit gene causes both decreased enzymatic activity and glutathione production

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Abstract
γ-Glutamylcysteine synthetase (γ-GCS) catalyzes the first and rate-limiting step in glutathione (GSH) biosynthesis: the adenosine triphosphate (ATP)–dependent ligation of glutamate and cysteine. γ-GCS consists of a catalytic (γ-GCSH) and modifier (γ-GCSL) subunit. Hereditary deficiency of γ-GCS has been reported in a small number of patients and is associated with low erythrocyte levels of γ-GCS and GSH leading to hemolytic anemia. Here we report a novel γ-GCSH mutation, isolated from the cDNA of 2 related patients diagnosed with γ-GCS deficiency. Each was found to be homozygous for a C>T missense mutation at nucleotide 379, encoding for a predicted Arg127Cys amino acid change. Computerized structure modeling identified that the mutated amino acid lies within a cleft on the protein surface of γ-GCSH, and the border of this cleft was shown to contain Cys249, an evolutionarily conserved residue that has been proven to lie near the binding site of γ-GCSH. Transfection studies showed that the mutation is associated with decreased GSH production, and binding studies using purified recombinant protein showed that the mutant protein has markedly decreased enzymatic activity compared to wild type.