Leiva, L. E. | Search bioRxiv

bioRxiv2024

Homocysteine thiolactone from translation proofreading is an endogenous ligand for cell-cell signaling by the receptor SdiA

Several widespread mechanisms enable cellular communication and coordinate the behavior of bacterial populations. The modules responsible for cellular communication are often found in matching pairs: an enzyme synthesizing a signal molecule and a specific receptor capable of decoding it. A notable exception is Escherichia coli SdiA, a homolog of known N-acyl homoserine lactone (AHL) receptors for which no corresponding AHL synthase exists. SdiA is an orphan receptor that enables cross-talk by sensing AHLs from other bacterial species. In this work, we investigated if homocysteine thiolactone (HTL), an AHL-like molecule arising from a proofreading reaction of methionyl tRNA synthetase (MetRS) to correct misactivation of homocysteine, participates in E. coli communication through SdiA. A comprehensive analysis of MetRS variants producing different levels of HTL showed more extended lag periods due to lower HTL levels, which were restored by HTL supplementation. SdiA mutants abolished the regulation of the transition from the lag phase to the exponential phase induced by HTL. Growth phenotypes were HTL-specific and were not induced by supplementation of other non-endogenous AHLs previously characterized as SdiA ligands. The gene expression of gadY and rmf regulated by SdiA was modulated by HTL supplementation. Through differential scanning fluorimetry, we show the SdiA-HTL interaction in vitro. Together, our observations describe HTL as an SdiA ligand capable of modulating cell-cell communication in bacteria.

molecular biology↗

bioRxiv2021

Enhanced translation of leaderless mRNAs under oxidative stress in Escherichia coli

The bacterial response to oxidative stress requires the adaptation of the proteome to the hostile environment. It has been reported that oxidative stress induces a strong and global inhibition of both, transcription and translation. Nevertheless, whereas it is well known that transcription of a small group of genes is induced thanks to transcription factors such as OxyR and SoxR, an equivalent mechanism has not been described for translation. Here we report that whereas canonical translation that depends on Shine Dalgarno recognition is inhibited by oxidative stress in Escherichia coli, the translation of leaderless mRNA (lmRNA) is enhanced under such conditions. Both, inhibition of canonical translation and enhancement of lmRNA translation, depend on the production of (p)ppGpp. We propose that such a mechanism would allow bacteria to rapidly adapt their proteome to hostile conditions and is, perhaps, a general strategy to confront strong stressful conditions. Significance statementThe regulation of translation (the production of proteins based on genetic information) is central for the adaptation to environmental changes. In Escherichia coli translation may begin through two alternative pathways. 1.- A canonical initiation that is well understood and is regulated mostly by changes in the accessibility of ribosomes to specific sequences and 2.- Initiation of leaderless mRNAs (lmRNAs) that lack these sequences and for which we do not understand the regulation process. Our results indicate that under oxidative stress, the production of (p)ppGpp in E. coli inhibits canonical translation and simultaneously enhances translation of lmRNAs, showing for the first time a natural condition where lmRNA translation is regulated and a role for (p)ppGpp in this process.

microbiology↗