The Escherichia coli YadB gene product reveals a novel aminoacyl-tRNA synthetase like activity

In the course of a structural genomics program aiming at solving the structures of Escherichia coli open reading frame products of unknown function, we have determined the structure of YadB at 1.5 Angstrom using molecular replacement. The YadB protein is 298 amino acid residues long and displays 34% sequence identity with E. coli glutamyl-tRNA synthetase (GluRS). It is much shorter than GluRS, which contains 468 residues, and lacks the complete domain interacting with the tRNA anticodon loop. As E. coli GluRS, YadB possesses a Zn2+ located in the putative dues as the first three zinc ligands, but has a weaker tyrosine ligand at the fourth position. It shares with canonical amino acid RNA synthetases a major functional feature, namely activation of the amino acid (here glutamate). It differs, however, from GluRSs by the fact that the activation step is tRNA-independent and that it does not catalyze attachment of the activated glutamate to E. coli tRNA(Glu), but to another, as yet unknown tRNA. These results suggest thus a novel function, distinct from that of GluRSs, for the yadB gene family. (C) 2004 Elsevier Ltd. All rights reserved.