Glu-tRNAGln amidotransferase or glutaminyl-tRNA synthase (glutamine-hydrolysing) enzyme () is an amidotransferase that catalyzes the conversion of the non-cognate amino acid glutamyl-tRNAGln to the cognate glutaminyl-tRNAGln.. It catalyzes the reaction: ATP + glutamyl-tRNAGln + L-glutamine ADP + phosphate + glutaminyl-tRNAGln + L-glutamate
This enzyme belongs to the family of ligases, specifically those forming carbon-nitrogen bonds carbon-nitrogen ligases with glutamine as amido-N-donor. The systematic name of this enzyme class is glutamyl-tRNAGln:L-glutamine amido-ligase (ADP-forming). This enzyme participates in glutamate metabolism and alanine and aspartate metabolism.
Function and evolutionary significance Most bacterial and all archaea genomes do not encode a glutaminyl-tRNA synthetase (GlnRS). Instead they first synthesize the attachment of an amino acid on the tRNAGln by first attaching a non-cognate glutamate to the tRNA. Then these organisms use the amidotransferase: glutaminyl-tRNA synthase (glutamine-hydrolysing) () enzyme to convert the glutamate attached to tRNAGln to glutamine.
Similarly, while humans possess a cytoplasmic Glutamine–tRNA ligase, QARS1, there is no apparent mitochondrial form of the enzyme. Instead, the non-discriminating enzyme, EARS2, first mischarges glutamate to tRNAGln, and then the GatCAB amidotransferase (AdT) complex (QRSL1-GATB-GATC) converts the glutamate to a glutamine.
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