title: Glutamine synthetase isoforms in nitrogen-fixing soybean nodules: distinct oligomeric structures and thiol-based regulation.
abstract: Legume root nodule glutamine synthetase (GS) catalyzes the assimilation of ammonia produced by nitrogen fixation. Two GS isoform subtypes (GS1β and GS1γ) are present in soybean nodules. GS1γ isoforms differ from GS1β isoforms in terms of their susceptibility to reversible inhibition by intersubunit disulfide bond formation between C159 and C92 at the shared active site at subunit interfaces. Although nodule GS enzymes share 86% amino acid sequence identity, analytical ultracentrifugation experiments showed that GS1γ is a dodecamer, whereas the GS1β is a decamer. It is proposed that this difference contributes to the differential thiol sensitivity of each isoform, and that GS1γ1 may be a target of thiol-based regulation.
authors.affiliation: Department of Biochemistry and Cellular and Molecular Biology, The University of Tennessee, Knoxville, TN 37996, United States.
authors.forename: Pintu D
authors.initials: PD
authors.lastname: Masalkar
authors.affiliation: Department of Biochemistry and Cellular and Molecular Biology, The University of Tennessee, Knoxville, TN 37996, United States; Program in Genome Science and Technology, The University of Tennessee, Knoxville, TN 37996, United States. Electronic address: drobert2@utk.edu.
authors.forename: Daniel M
authors.initials: DM
authors.lastname: Roberts
mesh_terms: D004220:Disulfides / Q000378:metabolism; D005974:Glutamate-Ammonia Ligase / Q000737:chemistry / Q000378:metabolism*; D007527:Isoenzymes / Q000737:chemistry / Q000378:metabolism; D008958:Models, Molecular; D020836:Protein Structure, Quaternary; D017434:Protein Structure, Tertiary; D013025:Glycine max / Q000201:enzymology*; D040681:Structural Homology, Protein
chemical_list: D004220:Disulfides; D007527:Isoenzymes; D005974:Glutamate-Ammonia Ligase
keywords: Analytical ultracentrifugation; Disulfide bond; Glutamine synthetase; Nitrogen assimilation; Symbiosis