Ammonia Channel Couples Glutaminase with Transamidase Reactions in GatCAB

Abstract

One-sentence summary: A series of X-ray crystal structures of bacterial Glu-tRNA Gln -dependent amidotransferase (GatCAB) in the apo form and in the substrate-bound states, combined with the biochemical studies, elucidate the sophisticated mechanism to synthesize Gln-tRNA Gln , coupling the glutaminase with the kinase and transamidase reactions by a characteristic ammonia channel 30 Å in length.

On the Evolution of the tRNA-Dependent Amidotransferases, GatCAB and GatDE

“…42 The tail domains in the AdT subunits play a similar role by enabling specific binding to their tRNA substrates. 21,22 Because YqeY is homologous to but more distantly related to GatB and GatE than they are to each other, it serves as an ideal outgroup for the tail domain phylogeny. Since, the GatE/GatB tail domain phylogeny is in general congruent with the phylogeny of the core of the enzymes, the tail domain is an adequate phylogenetic marker for the entire molecule.…”

“…It shows homology to the tail domain of both subunits. [21][22][23] YqeY is found in a diverse array of bacteria across multiple phyla but their function remains unknown. 42 A YqeY domain appended to the C-terminus of the Deinococcus radiodurans GlnRS is important for the enzyme to productively bind to tRNA Gln .…”

“…1). 3,[21][22][23]31 The latter enzymes are encoded in the nuclear genomes of many eukaryotes. 31 In Saccharomyces cerevisiae, Pet112 is essential for mitochondrial translation.…”

“…2, 10, 21, 24 GatC, a small protein of approximately 100 amino acids, is required by GatA for proper folding 10 and binding to GatB. 21 3) The AdTs amidate the activated intermediate using the ammonia liberated by the glutaminase subunit.…”

“…19 This kinase activity is the province of the B and E-subunits of the respective holoenzymes. [20][21][22] 2) The AdTs have a glutaminase subunit (GatA and GatD, respectively) to liberate ammonia from an amide donor such as Gln or Asn. 2,20,23,24 GatD belongs to the type I L-asparaginase (AnsA) family 3, 20, 23 while GatA is an amidase.…”