Compensating Complete Loss of Signal Recognition Particle During Co-translational Protein Targeting by the Translation Speed and Accuracy.

Liuqun Zhao,Yanyan Cui,Tao Cai,Zixiang Xu,Dawei Zhang,Gang Fu

doi:10.3389/fmicb.2021.690286

Abstract

Signal recognition particle (SRP) is critical for delivering co-translational proteins to the bacterial inner membrane. Previously, we identified SRP suppressors in Escherichia coli that inhibit translation initiation and elongation, which provided insights into the mechanism of bypassing the requirement of SRP. Suppressor mutations tended to be located in regions that govern protein translation under evolutionary pressure. To test this hypothesis, we re-executed the suppressor screening of SRP. Here, we isolated a novel SRP suppressor mutation located in the Shine–Dalgarno sequence of the S10 operon, which partially offset the targeting defects of SRP-dependent proteins. We found that the suppressor mutation decreased the protein translation rate, which extended the time window of protein targeting. This increased the possibility of the correct localization of inner membrane proteins. Furthermore, the fidelity of translation was decreased in suppressor cells, suggesting that the quality control of translation was inactivated to provide an advantage in tolerating toxicity caused by the loss of SRP. Our results demonstrated that the inefficient protein targeting due to SRP deletion can be rescued through modulating translational speed and accuracy.

Highlights

The signal recognition particle (SRP) is a highly conserved ribonucleoprotein complex that is involved in co-translational targeting of the ribosome-nascent chain complex to the endoplasmic reticulum of eukaryotes or the inner membrane of prokaryotes (Walter and Johnson, 1994; Pool, 2005)
We reported that SRP was nonessential in Escherichia coli, and slowing translation speed played a critical role in membrane protein targeting
A moderate decrease in translation fidelity ensured a suitable translation speed for better cell growth

Summary

Introduction

The signal recognition particle (SRP) is a highly conserved ribonucleoprotein complex that is involved in co-translational targeting of the ribosome-nascent chain complex to the endoplasmic reticulum of eukaryotes or the inner membrane of prokaryotes (Walter and Johnson, 1994; Pool, 2005). The E. coli SRP components can replace their mammalian homologs to mediate efficient co-translational protein targeting of mammalian proteins (Bernstein et al, 1993; Powers and Walter, 1997). This suggests that the subunit SRP54 and domain IV of Translational Control Regulates Protein Targeting the 7S SRP RNA form the core elements of SRP, and SRP is remarkably conserved from bacteria to mammals. SRP is primarily responsible for delivering inner membrane proteins (Ulbrandt et al, 1997; Zhang and Shan, 2014) It recognizes hydrophobic transmembrane domains or signal sequences when they emerge from the ribosome exit tunnel (Ng et al, 1996). Given the crowded cellular environment, it is challenging to correctly translocate newly synthesized proteins from the cytosol to the membrane

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Discussion

Conclusion