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A‐Loop Residues in Glutathione Synthetase
Author(s) -
Brown T.,
Dinescu A.,
Cundari T.R.,
Anderson M. E.
Publication year - 2007
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.21.6.a1011-c
Subject(s) - glutathione synthetase , glutathione , dipeptide , glycine , cysteine , tripeptide , serine , mutant , biochemistry , amino acid , protein subunit , chemistry , alanine , biology , enzyme , gene
Glutathione (GSH), an important tripeptide found in all living cells, functions as an antioxidant and intracellular thiol source. GSH is synthesized in two ATP‐dependent steps. The first step is the formation of the dipeptide γ‐glutamylcysteine from glutamate and cysteine, catalyzed by γ‐glutamylcysteine synthetase. Glutathione synthetase (GS) ligates the dipeptide with glycine to form GSH. Human GS (hGS) is a homodimer. Each subunit has an active site and is composed of 474 residues. The subunit has three important loop structures. One is the alanine‐rich, A‐loop. It is located near the C‐terminal and the glycine binding site. The A‐loop is composed of thirteen residues. For higher eukaryotes, the A‐loop sequence has ~90% identity with hGS. However, lower eukaryotes and prokaryotes only have ~45%. In addition, there is a patient with a mutation in the A‐loop, G464V; symptoms are recurrent bacterial infections, mental retardation, and severe metabolic acidosis (5‐oxoprolinuria). These suggest that the A‐loop is important for GS function. We prepared several A‐loop mutants (G464V and G459S) and have found significantly lowered activity (<10%). Our A‐loop studies further the understanding of its role in the production of GSH. (Supported by a Faculty Enhancement Program Grant TWU (MEA), a Welch Foundation Grant (Chem. Dept. TWU), U.S. Dept. Ed (CASCaM UNT, T.R.C.), Faculty Research Grant UNT (T.R.C.).