Atomic Structure of Plant Glutamine Synthetase
Journal of Biological Chemistry
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
... f 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. * This work was supported by the Ministry of Education, Culture, Sports, Science, and Technology (MEXT), Japan. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. □ S The on-line version of this article (available at http://www.jbc.org) contains supplemental Figs. S1 and S2. The atomic coordinates and structure factors (code 2D3A, 2D3B, and 2D3C) have been deposited in the Protein 7 The abbreviations used are: GS, glutamine synthetase; MetSox-P, methionine sulfoximine phosphate; PEG, polyethylene glycol; MetSox, methionine sulfoximine; PPT-P, phosphinothricin phosphate; AMPPNP, adenylyl imidodiphosphate; PPT, phosphinothricin; NCS, non-crystallographic symmetry. http://www.jbc.org/ Downloaded from FIGURE 4. Representation of the interactions between enzyme and substrate analogues. a, stick models for the interaction of the enzyme with AMPPNP and MetSox. Carbon, oxygen, nitrogen, phosphorus, and sulfur atoms are colored gray, red, blue, salmon, and yellow, respectively. Three Mn 2ϩ are indicated in pink spheres. Dotted lines designate hydrogen bonds and coordination bonds to Mn 2ϩ ions. Residues without dotted lines have hydrophobic interactions with the substrate. b, stick models for the interaction of the enzyme with ADP and MetSox. c, stick models for the interaction of the enzyme with ADP and PPT-P.