Glutamine amidotransferases (GATs), which catalyze the synthesis of different aminated products, channel ammonia over 10-40 A from a glutamine substrate at the glutaminase site to an acceptor substrate at the synthase site. Ammonia production usually uses a cysteine-histidine-glutamate triad or a N-terminal cysteine residue. Crystal structures of several amidotransferase ligand complexes, mimicking intermediates along the catalytic cycle, have now been determined. In most cases, acceptor binding triggers glutaminase activation through domain-hinged movements and other conformational changes. Structural information shows how flexible loops of the synthase and glutaminase domains move to shield the two catalytic sites and anchor the substrates, and how the ammonia channel forms and opens or closes.

Background:The C5-hydroxylation reaction of coenzyme Q biosynthesis in Escherichia coli is catalyzed by an unknown enzyme. Results: The UbiI protein is responsible for the C5-hydroxylation reaction. Conclusion:The three monooxygenases involved in aerobic Q biosynthesis are now identified. Significance: We report the characterization of a gene of unknown function and the first crystal structure of a monooxygenase involved in Q biosynthesis.