ArfB can displace mRNA to rescue stalled ribosomes.
ArfB can displace mRNA to rescue stalled ribosomes.
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DOI：
10.1038/s41467-020-19370-z
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发表时间：
2020-11-03
影响因子：
16.6
通讯作者：
Korostelev AA
中科院分区：
文献类型：
--
作者：
Carbone CE;Demo G;Madireddy R;Svidritskiy E;Korostelev AA
在翻译过程中停滞的核糖体必须被拯救，以补充有翻译能力的核糖体亚基库。细菌替代拯救因子B（Arf B）从在A位点截短的mRNA上停滞的核糖体释放新生肽，允许核糖体再循环。先前的结构研究表明，ArfB通过将其C-末端α-螺旋插入到空的mRNA隧道中来识别这样的核糖体。在这项工作中，我们报告说，ArfB可以有效地识别更广泛的mRNA底物，包括较长的mRNA，延伸到A位点密码子之外。单颗粒冷冻EM揭示了ArfB根据mRNA长度采用两种功能模式。ArfB作为单体在核糖体A位点容纳较短的mRNA。相比之下，较长的mRNA从mRNA隧道中被置换超过20 μ m，并通过二聚体ArfB稳定在亚基间空间中。揭示ArfB功能的不同模式解决了相互矛盾的生化和结构研究，并可能导致重新检查其他核糖体救援途径，其功能取决于mRNA的长度。替代拯救因子B（Arf B）是一种从停滞的核糖体释放肽以允许核糖体再循环的酶。在这里，作者对短或长mRNA上与ArfB复合的70 S核糖体进行了冷冻电镜分析，以揭示ArfB功能的不同模式。
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. Alternative rescue factor B (ArfB) is an enzyme that releases peptides from stalled ribosomes to allow ribosome recycling. Here the authors carry-out cryo-EM analyses of 70S ribosomes complexed with ArfB on either a short or longer mRNA to reveal distinct modes of ArfB function.
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