title: Atomic structure of plant glutamine synthetase: a key enzyme for plant productivity.
abstract: Plants provide nourishment for animals and other heterotrophs as the sole primary producer in the food chain. Glutamine synthetase (GS), one of the essential enzymes for plant autotrophy catalyzes the incorporation of ammonia into glutamate to generate glutamine with concomitant hydrolysis of ATP, and plays a crucial role in the assimilation and re-assimilation of ammonia derived from a wide variety of metabolic processes during plant growth and development. Elucidation of the atomic structure of higher plant GS is important to understand its detailed reaction mechanism and to obtain further insight into plant productivity and agronomical utility. Here we report the first crystal structures of maize (Zea mays L.) GS. The structure reveals a unique decameric structure that differs significantly from the bacterial GS structure. Higher plants have several isoenzymes of GS differing in heat stability and catalytic properties for efficient responses to variation in the environment and nutrition. A key residue responsible for the heat stability was found to be Ile-161 in GS1a. The three structures in complex with substrate analogues, including phosphinothricin, a widely used herbicide, lead us to propose a mechanism for the transfer of phosphate from ATP to glutamate and to interpret the inhibitory action of phosphinothricin as a guide for the development of new potential herbicides.
authors.affiliation: Institute for Protein Research, Osaka University, 3-2 Yamada-oka, Suita, Osaka, Japan.
authors.forename: Hideaki
authors.initials: H
authors.lastname: Unno
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Uchida
authors.forename: Hajime
authors.initials: H
authors.lastname: Sugawara
authors.forename: Genji
authors.initials: G
authors.lastname: Kurisu
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Sugiyama
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Yamaya
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Sakakibara
authors.forename: Toshiharu
authors.initials: T
authors.lastname: Hase
authors.forename: Masami
authors.initials: M
authors.lastname: Kusunoki
mesh_terms: D000255:Adenosine Triphosphate / Q000737:chemistry; D000595:Amino Acid Sequence; D002384:Catalysis; D004926:Escherichia coli / Q000378:metabolism; D005974:Glutamate-Ammonia Ligase / Q000737:chemistry*; D018698:Glutamic Acid / Q000737:chemistry; D006358:Hot Temperature; D006868:Hydrolysis; D007532:Isoleucine / Q000737:chemistry; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011994:Recombinant Proteins / Q000737:chemistry; D017386:Sequence Homology, Amino Acid; D003313:Zea mays / Q000201:enzymology*
chemical_list: D011994:Recombinant Proteins; D007532:Isoleucine; D018698:Glutamic Acid; D000255:Adenosine Triphosphate; D005974:Glutamate-Ammonia Ligase