Gln49 and Ser174 residues play critical roles in determining the catalytic efficiencies of plant glutamine synthetase.
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.
Ishiyama
Keiki
K
RIKEN Plant Science Center, Yokohama, 230-0045 Japan.
Inoue
Eri
E
Yamaya
Tomoyuki
T
Takahashi
Hideki
H
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
D007527:Isoenzymes; D000644:Quaternary Ammonium Compounds; D005973:Glutamine; D012694:Serine; D005974:Glutamate-Ammonia Ligase; D008239:Lysine; D000409:Alanine