Substrate recognition mechanism of tRNA-targeting ribonuclease, colicin D, and an insight into tRNA cleavage-mediated translation impairment
Tetsuhiro Ogawa*, Kazutoshi Takahashi, Wataru Ishida, Toshihiro Aono, Makoto Hidaka, Tohru Terada, Haruhiko Masaki*
Colicin D is a plasmid-encoded bacteriocin that specifically cleaves tRNAArg of sensitive Escherichia coli cells. E. coli has four isoaccepting tRNAArgs; the cleavage occurs at the 3′ end of anticodon-loop, leading to translation impairment in the sensitive cells. tRNAs form a common L-shaped structure and have many conserved nucleotides that limit tRNA identity elements. How colicin D selects tRNAArgs from the tRNA pool of sensitive E. coli cells is therefore intriguing. Here, we reveal the recognition mechanism of colicin D via biochemical analyses as well as structural modelling. Colicin D recognizes tRNAArg ICG, the most abundant species of E. coli tRNAArgs, at its anticodon-loop and D-arm, and selects it as the most preferred substrate by distinguishing its anticodon-loop sequence from that of others. It has been assumed that translation impairment is caused by a decrease in intact tRNA molecules due to cleavage. However, we found that intracellular levels of intact tRNAArg ICG do not determine the viability of sensitive cells after such cleavage; rather, an accumulation of cleaved ones does. Cleaved tRNAArg ICG dominant-negatively impairs translation in vitro. Moreover, we revealed that EF-Tu, which is required for the delivery of tRNAs, does not compete with colicin D for binding tRNAArg ICG, which is consistent with our structural model. Finally, elevation of cleaved tRNAArg ICG level decreases the viability of sensitive cells. These results suggest that cleaved tRNAArg ICG transiently occupies ribosomal A-site in an EF-Tu-dependent manner, leading to translation impairment. The strategy should also be applicable to other tRNA-targeting RNases, as they, too, recognize anticodon-loops.
- : RNA Biology
- : 10.1080/15476286.2020.1838782
- : https://www.tandfonline.com/doi/full/10.1080/15476286.2020.1838782