This region contains the Glutathionylspermidine synthase enzymatic activity EC:6.3.1.8. This is the C-terminal region in bi-enzymes such as Swiss:P43675. Glutathionylspermidine (GSP) synthetases of Trypanosomatidae and Escherichia coli couple hydrolysis of ATP (to ADP and Pi) with formation of an amide bond between spermidine and the glycine carboxylate of glutathione (gamma-Glu-Cys-Gly). In the pathogenic trypanosomatids, this reaction is the penultimate step in the biosynthesis of the antioxidant metabolite, trypanothione (N1,N8-bis-(glutathionyl)spermidine), and is a target for drug design [1]. This region, the pre-ATP grasp region, probably carries the substrate-binding site [2].

1: Glutathionylspermidine metabolism in Escherichia coli. Purification, cloning, overproduction, and characterization of a bifunctional glutathionylspermidine synthetase/amidase. Bollinger JM Jr, Kwon DS, Huisman GW, Kolter R, Walsh CT; J Biol Chem 1995;270:14031-14041. PMID:7775463

2: Dual binding sites for translocation catalysis by Escherichia coli glutathionylspermidine synthetase. Pai CH, Chiang BY, Ko TP, Chou CC, Chong CM, Yen FJ, Chen S, Coward JK, Wang AH, Lin CH; EMBO J. 2006;25:5970-5982. PMID:17124497