ArfB can displace mRNA to rescue stalled ribosomes

Christine E. Carbone, Gabriel Demo, Rohini Madireddy, Egor Svidritskiy () and Andrei A. Korostelev ()
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Christine E. Carbone: UMass Medical School
Gabriel Demo: UMass Medical School
Rohini Madireddy: UMass Medical School
Egor Svidritskiy: UMass Medical School
Andrei A. Korostelev: UMass Medical School

Nature Communications, 2020, vol. 11, issue 1, 1-9

Abstract: Abstract Ribosomes stalled during translation must be rescued to replenish the pool of translation-competent ribosomal subunits. Bacterial alternative rescue factor B (ArfB) releases nascent peptides from ribosomes stalled on mRNAs truncated at the A site, allowing ribosome recycling. Prior structural work revealed that ArfB recognizes such ribosomes by inserting its C-terminal α-helix into the vacant mRNA tunnel. In this work, we report that ArfB can efficiently recognize a wider range of mRNA substrates, including longer mRNAs that extend beyond the A-site codon. Single-particle cryo-EM unveils that ArfB employs two modes of function depending on the mRNA length. ArfB acts as a monomer to accommodate a shorter mRNA in the ribosomal A site. By contrast, longer mRNAs are displaced from the mRNA tunnel by more than 20 Å and are stabilized in the intersubunit space by dimeric ArfB. Uncovering distinct modes of ArfB function resolves conflicting biochemical and structural studies, and may lead to re-examination of other ribosome rescue pathways, whose functions depend on mRNA lengths.

Date: 2020
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DOI: 10.1038/s41467-020-19370-z

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