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Structure–function studies of glutamate synthases: A class of self‐regulated iron‐sulfur flavoenzymes essential for nitrogen assimilation
Author(s) -
Vai Maria Antonietta,
Curti Bruno
Publication year - 2008
Publication title -
iubmb life
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.132
H-Index - 113
eISSN - 1521-6551
pISSN - 1521-6543
DOI - 10.1002/iub.52
Subject(s) - glutamate synthase , glutamine amidotransferase , cofactor , ferredoxin , oxidoreductase , nad+ kinase , chemistry , biochemistry , atp synthase , stereochemistry , flavin mononucleotide , active site , enzyme , glutamine synthetase , glutamine , biology , amino acid
Glutamate synthases play with glutamine synthetase an essential role in nitrogen assimilation processes in microorganisms, plants, and lower animals by catalyzing the net synthesis of one molecule of L ‐glutamate from L ‐glutamine and 2‐oxoglutarate. They exhibit a modular architecture with a common subunit or region, which is responsible for the L ‐glutamine‐dependent glutamate synthesis from 2‐oxoglutarate. Here, a PurF‐ (Type II‐ or Ntn‐) type amidotransferase domain is coupled to the synthase domain, a (β/α) 8 barrel containing FMN and one [3Fe‐4S] 0,+1 cluster, through a ∼30 Å‐long intramolecular tunnel for the transfer of ammonia between the sites. In bacterial and eukaryotic GltS, reducing equivalents are provided by reduced pyridine nucleotides thanks to the stable association with a second subunit or region, which acts as a FAD‐dependent NAD(P)H oxidoreductase and is responsible for the formation of the two low potential [4Fe‐4S] +1,+2 clusters of the enzyme. In photosynthetic cells, reduced ferredoxin is the physiological reductant. This review focus on the mechanism of cross‐activation of the synthase and glutaminase reactions in response to the bound substrates and the redox state of the enzyme cofactors, as well as on recent information on the structure of the αβ protomer of the NADPH‐dependent enzyme, which sheds light on the intramolecular electron transfer pathway between the flavin cofactors. © 2008 IUBMB IUBMB Life, 60(5): 287–300, 2008

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