title: Gln49 and Ser174 residues play critical roles in determining the catalytic efficiencies of plant glutamine synthetase.
abstract: Two essential residues playing critical roles in determining the substrate specificities of cytosolic glutamine synthetase (GS1) have been identified from the alignment of high-affinity (GLN1;1 and GLN1;4) and low-affinity (GLN1;2 and GLN1;3) GS1 isoenzymes in Arabidopsis, and confirmed by site-directed mutagenesis. The results indicated that either K49Q or A174S mutation is sufficient to increase the catalytic efficiencies of GLN1;3 by decreasing its Km values for ammonium. In contrast, replacement of Gln49 and Ser174 by lysine and alanine, respectively, was detrimental to glutamine synthetic activities in GLN1;4. The results suggested that Gln49 and Ser174 in the high-affinity GS1 isoenzymes are interchangeable with Lys49 and Ala174 in the low-affinity variants at the corresponding positions.
authors.affiliation: RIKEN Plant Science Center, Yokohama, 230-0045 Japan.
authors.forename: Keiki
authors.initials: K
authors.lastname: Ishiyama
authors.forename: Eri
authors.initials: E
authors.lastname: Inoue
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Yamaya
authors.forename: Hideki
authors.initials: H
authors.lastname: Takahashi
mesh_terms: D000409:Alanine / Q000032:analysis; D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology*; D002384:Catalysis; D005974:Glutamate-Ammonia Ligase / Q000737:chemistry* / Q000378:metabolism*; D005973:Glutamine / Q000032:analysis / Q000502:physiology*; D007527:Isoenzymes / Q000737:chemistry / Q000378:metabolism; D008239:Lysine / Q000032:analysis; D008969:Molecular Sequence Data; D009154:Mutation; D000644:Quaternary Ammonium Compounds / Q000378:metabolism; D012694:Serine / Q000032:analysis / Q000502:physiology*; D013379:Substrate Specificity
chemical_list: D007527:Isoenzymes; D000644:Quaternary Ammonium Compounds; D005973:Glutamine; D012694:Serine; D005974:Glutamate-Ammonia Ligase; D008239:Lysine; D000409:Alanine