Ribosome-inactivation by a widely distributed class of C-tail anchored membrane proteins

Ribosome hibernation is a commonly used strategy that protects ribosomes under unfavorable conditions and regulates developmental processes. Multiple ribosome-hibernation factors have been identified in all domains of life, but due to their structural diversity and the lack of a common mechanism by which they inactivate ribosomes, it is currently unknown how many different hibernation factors exist. Here, we demonstrate that the YqjD/ElaB/YgaM protein family constitute an abundant class of ribosome-hibernating proteins and represent the first membrane-bound hibernating factors identified in bacteria. Our data demonstrate that they interact with 50S ribosomal subunit and show a concentration-dependent inhibition of protein synthesis. By combining in vivo cross-linking with mass spectrometry, we show that they bind via their N-termini to proteins that surround the ribosomal tunnel exit and even penetrate into the ribosomal tunnel. Thus, YqjD/ElaB/YgaM inhibit translation by blocking the ribosomal tunnel and thus mimic the activity of antimicrobial peptides and macrolide antibiotics.