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 of L-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 substrate L-glutamine.
Structural studies on the synchronization of catalytic centers in glutamate synthase / Van Den Heuvel, R. H. H.; Ferrari, D.; Bossi, R. T.; Ravasio, S.; Curti, B.; Vanoni, M. A.; Florencio, F. J.; Mattevi, A.. - In: THE JOURNAL OF BIOLOGICAL CHEMISTRY. - ISSN 0021-9258. - 277:27(2002), pp. 24579-24583. [10.1074/jbc.M202541200]
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