Structural Studies on the Synchronization of Catalytic Centers in Glutamate Synthase

• Published in: The Journal of biological chemistry Vol. 277; no. 27; pp. 24579 - 24583
• Main Authors: van den Heuvel, Robert H.H., Ferrari, Davide, Bossi, Roberto T., Ravasio, Sergio, Curti, Bruno, Vanoni, Maria A., Florencio, Francisco J., Mattevi, Andrea
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 05-07-2002; American Society for Biochemistry and Molecular Biology
• Subjects: Amino Acid Oxidoreductases - chemistry; Amino Acid Oxidoreductases - metabolism; Catalytic Domain; Crystallography, X-Ray; Cyanobacteria - enzymology; Ferredoxins - metabolism; Glutamate Synthase - chemistry; Glutamate Synthase - metabolism; Models, Molecular; Oxidation-Reduction; Protein Conformation
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M202541200

The complex iron-sulfur flavoprotein glutamate synthase (GltS) plays a prominent role in ammonia assimilation in bacteria, yeasts, and plants. GltS catalyzes the formation of two molecules of l-glutamate from 2-oxoglutarate and l-glutamine via intramolecular channeling of ammonia. GltS has the impressive ability of synchronizing its distinct catalytic centers to avoid wasteful consumption ofl-glutamine. We have determined the crystal structure of the ferredoxin-dependent GltS in several ligation and redox states. The structures reveal the crucial elements in the synchronization between the glutaminase site and the 2-iminoglutarate reduction site. The structural data combined with the catalytic properties of GltS indicate that binding of ferredoxin and 2-oxoglutarate to the FMN-binding domain of GltS induce a conformational change in the loop connecting the two catalytic centers. The rearrangement induces a shift in the catalytic elements of the amidotransferase domain, such that it becomes activated. This machinery, over a distance of more than 30 Å, controls the ability of the enzyme to bind and hydrolyze the ammonia-donating substratel-glutamine.