Assembling and powering ribosomes are energy-intensive processes requiring fine-tuned cellular control mechanisms. In organisms operating under strict nutrient limitations, such as pathogenic microsporidia, conservation of energy via ribosomal hibernation and recycling is critical. The mechanisms by which hibernation is achieved in microsporidia, however, remain poorly understood. Here, we present the cryo–electron microscopy structure of the ribosome from Paranosema locustae spores, bound by the conserved eukaryotic hibernation and recycling factor Lso2. The microsporidian Lso2 homolog adopts a V-shaped conformation to bridge the mRNA decoding site and the large subunit tRNA binding sites, providing a reversible ribosome inactivation mechanism. Although microsporidian ribosomes are highly compacted, the P. locustae ribosome retains several rRNA segments absent in other microsporidia, and represents an intermediate state of rRNA reduction. In one case, the near complete reduction of an expansion segment has resulted in a single bound nucleotide, which may act as an architectural co-factor to stabilize a protein–protein interface. The presented structure highlights the reductive evolution in these emerging pathogens and sheds light on a conserved mechanism for eukaryotic ribosome hibernation.

组装核糖体并为其提供动力是耗费能量的过程，需要微调的细胞控制机制。在严格的营养限制条件下运行的生物中，例如致病性微孢子虫，通过核糖体冬眠和循环利用来保存能量至关重要。然而，在小孢子虫中实现冬眠的机制仍然知之甚少。在这里，我们介绍了寄生偏执狂孢子虫核糖体的冷冻-电子显微镜结构，受保守的真核冬眠和循环因子Lso2的束缚。微孢子虫Lso2同源物采用V形构型，桥接mRNA解码位点和大亚基tRNA结合位点，提供了可逆的核糖体失活机制。尽管微孢子虫核糖体高度紧密，P。刺槐核糖体保留了其他微孢子虫中不存在的几个rRNA片段，代表rRNA还原的中间状态。在一种情况下，扩展区段的几乎完全还原导致了一个单核苷酸的结合，这可以作为稳定蛋白质-蛋白质界面的结构辅助因子。提出的结构突出了这些新兴病原体的还原性进化，并阐明了真核核糖体冬眠的保守机制。