Molecular basis of glutathione synthetase deficiency and a rare gene permutation event

Glutathione synthetase (GS) catalyses the production of glutathione from ga mma-glutamylcysteine and glycine in an ATP-dependent manner, Malfunctioning of GS results in disorders including metabolic acidosis, 5-oxoprolinuria, neurological dysfunction, haemolytic anaemia and in some cases is probably lethal. Here we report the crystal structure of human GS (hGS) at 2.1 Angst rom resolution in complex with ADP, two magnesium ions, a sulfate ion and g lutathione, The structure indicates that hGS belongs to the recently identi fied ATP-grasp superfamily, although it displays no detectable sequence ide ntity with other family members including its bacterial counterpart, Escher ichia coli GS, The difficulty in identifying hGS as a member of the family is due in part to a rare gene permutation which has resulted in a circular shift of the conserved secondary structure elements in hGS with respect to the other known ATP-grasp proteins. Nevertheless, it appears likely that th e enzyme shares the same general catalytic mechanism as other ligases. The possibility of cyclic permutations provides an insight into the evolution o f this family and will probably lead to the identification of new members. Mutations that lead to GS deficiency have been mapped onto the structure, p roviding a molecular basis for understanding their effects.