Abstract
The canonical function of glutamyl-tRNA synthetase (GluRS) is to
glutamylate tRNAGlu. Yet, not all bacterial GluRSs
glutamylate tRNAGlu; many glutamylate both
tRNAGlu and tRNAGln, while some
glutamylate only tRNAGln and not the cognate substrate
tRNAGlu. Understanding the basis of this unique
tRNAGlx-specificity is important. Mutational studies
have hinted at hotspot residues, both on tRNAGlx and
GluRS, that play crucial roles in tRNAGlx-specificity.
But the underlying structural basis remains unexplored. Majority of
biochemical studies related to tRNAGlx-specificity
have been performed on GluRS from Escherichia coli and other
proteobacterial species. However, since the early crystal structures of
GluRS and tRNAGlu-bound GluRS were from
non-proteobacterial species (Thermus thermophilus ), the
proteobacterial biochemical data have often been interpreted in the
context of non-proteobacterial GluRS structures. Marked differences
between proteo- and non-proteobacterial GluRSs have been demonstrated
and therefore it is important that tRNAGlx-specificity
be understood vis-a-vis proteobacterial GluRS structures. Towards this
goal we have solved the crystal structure of GluRS from E. coli .
Using the solved structure and several other currently available proteo-
and non-proteobacterial GluRS crystal structures, we have probed the
structural basis of tRNAGlx-specificity of bacterial
GluRSs. Specifically, our analysis suggests a unique role played by a
tRNAGlx D-helix contacting loop of GluRS in modulation
of tRNAGln-specificity. While earlier studies had
identified functional hotspots on tRNAGlx that
controlled tRNAGlx-specificity of GluRS, this is the
first report of complementary signatures of
tRNAGlx-specificity in GluRS.
A short running title: tRNAGlx-specific
signatures in GluRS
Key words: GluRS, tRNA-Gln, tRNA-discrimination, E. coli ,
proteobacteria, protein-RNA interaction