Trans-oligomerization of duplicated aminoacyl-tRNA synthetases maintains genetic code fidelity under stress

Abstract

Aminoacyl-tRNA synthetases (aaRSs) play a key role in deciphering the genetic message by producing charged tRNAs and are equipped with proofreading mechanisms to ensure correct pairing of tRNAs with their cognate amino acid. Duplicated aaRSs are very frequent in Nature, with 25,913 cases observed in 26,837 genomes. The oligomeric nature of many aaRSs raises the question of how the functioning and oligomerization of duplicated enzymes is organized. We characterized this issue in a model prokaryotic organism that expresses two different threonyl-tRNA synthetases, responsible for Thr-tRNAThr synthesis: one accurate and constitutively expressed (T1) and another (T2) with impaired proofreading activity that also generates mischarged Ser-tRNAThr. Low zinc promotes dissociation of dimeric T1 into monomers deprived of aminoacylation activity and simultaneous induction of T2, which is active for aminoacylation under low zinc. T2 either forms homodimers or heterodimerizes with T1 subunits that provide essential proofreading activity in trans. These findings evidence that in organisms with duplicated genes, cells can orchestrate the assemblage of aaRSs oligomers that meet the necessities of the cell in each situation. We propose that controlled oligomerization of duplicated aaRSs is an adaptive mechanism that can potentially be expanded to the plethora of organisms with duplicated oligomeric aaRSs.

A threonyl-tRNA synthetase-like protein has tRNA aminoacylation and editing activities

“…For ThrRS systems, duplicated ThrRS genes have recently been reported in the cyanobacterial genus Anabaena . Both ThrRSs (T1 and T2) have tRNA Thr aminoacylation activity; however, only the constitutively expressed T1 has an editing function; the conditionally expressed T2 is editing-deficient and present only in conditions of zinc deprivation ( 39 ). Here, both mThrRS and mThrRS-L have editing activities.…”

The K296-D320 region of recombinant levansucrase BA-SacB can affect the sensitivity of Escherichia coli host to sucrose

“…It is well known that insertional inactivation of a plasmidborne SacB expression cassette can be used for selection of bacterial clones containing recombinant DNA inserts. Therefore, SacB genes have been widely used for marker exchange procedures to trap insertion sequences (Thulin et al 2015;Sawisit et al 2015;Rubio et al 2015;Weissman 2016). There are two hypotheses to explain the lethality of SacB in the presence of sucrose: (i) production of toxic metabolites by transfer of fructose residues to inappropriate acceptor molecules (Pelicic et al 1996;Dziewit and Bartosik 2015;Khetrapal et al 2015), and (ii) accumulation of levan in the periplasm might disrupt periplasmic functions (Jäger et al 1992;Pelicic et al 1996).…”

Sub-Cellular Localization and Complex Formation by Aminoacyl-tRNA Synthetases in Cyanobacteria: Evidence for Interaction of Membrane-Anchored ValRS with ATP Synthase

“…To investigate this, Anabaena strains were engineered to express each aaRSs fused to GFP from the petE inducible promoter and the subcellular localization of the fusion proteins was monitored by confocal fluorescence microscopy. Anabaena contains duplicated ThrRSs, named T1 and T2, (Napolitano et al, 2012 ; Rubio et al, 2015 ) and similar to many other bacteria, it lacks a GlnRS, Gln-tRNA Gln being synthesized through the indirect pathway (Schon et al, 1986 ; Luque et al, 2008 ). For hetero-oligomeric aaRSs, namely GlyRS and PheRS, only one construct fusing the α subunit to GFP was made.…”