Glu-tRNAGln-dependent amidotransferase GatCAB


The formation of Gln-tRNAGln differs among the three domains of life. Most bacteria employ an indirect pathway to produce Gln-tRNAGln by a heterotrimeric amidotransferase, GatCAB, in a mis-acylated Glu-tRNAGln-dependent manner. Hampered by the absence of an atomic model, very little is known about the molecular mechanism responsible for the sophisticated coupling reactions of GatCAB. Here, we report the three first crystal structures of intact GatCAB complex from Staphylococcus aureus, in the apo form, the glutamine- and the ATP analog-bound states. Two identified active sites are markedly distant but connected by an idiosyncratic ammonia channel 30 angstrom in length. Furthermore, we also clarified identity elements essential for discrimination of tRNAGln, and propose a complete model for the overall concerted reactions to generate Gln-tRNAGln by GatCAB.


Figure Caption

GatCAB converts Glu-tRNAGln into Gln-tRNAGln. In this reaction, initially Glu-tRNAGln is activated using ATP in GatB (green), subsequently activated Glu-tRNAGln is transamidated into Gln-tRNAGln using ammonia generated by hydrolysis of glutamine in GatA (blue). Two identified reaction centers in GatA and GatB are markedly distant but connected by a long channel (orange), which transfers generated ammonia from GatA to GatB.


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