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Ribosomes, the cell’s protein-making factories, consume large amounts of energy as they build the proteins that keep cells alive and functioning. When cells experience stress - such as lack of nutrients or sudden drops in temperature - they quickly switch into survival mode. New research from the Schuman Lab at the Max Planck Institute for Brain Research in Frankfurt now reveals an unexpected way cells manage this transition: By pairing up inactive ribosomes using a ribosomal RNA link. This RNA-based mechanism reveals a previously unknown role for ribosomal RNA in the cellular stress response.
Ribosomes are large molecular machines made of protein and RNA that build all proteins in the cell. Because protein production is extremely energy-intensive, cells rapidly reduce protein synthesis when stressed. It has long been known that bacterial cells pair their inactive ribosomes into so-called “hibernating disomes” however, such structures had not previously been identified in animal cells.
An unexpected role for ribosomal RNA during cellular stress
Using advanced imaging techniques, Erin Schuman and her team at the Department of Synaptic Plasticity at the Max Planck Institute for Brain Research in Frankfurt discovered that stressed animal cells - including neurons - assemble inactive ribosomes into tightly linked pairs, known as disomes. These ribosome pairs are not accidental collisions or artifacts, but a regulated and reversible response to stress. The new study was published today in Science.
“Surprisingly, the two ribosomes are not held together by proteins, as is common in bacteria. Instead, the connection is made by a specific piece of ribosomal RNA called an expansion segment”, explains one of the lead authors, postdoctoral researcher, Andre Schwarz.
Expansion segments are long, flexible RNA “tentacles” that protrude from ribosomes and have grown larger over the course of evolution. Although they are a prominent feature of animal ribosomes, their functions only just started to emerge. This study now shows that one particular expansion segment, called “31b”, is both necessary and sufficient to link ribosomes together during stress. At the molecular level, the expansion segment forms a precise RNA-RNA interaction - a so-called “kissing loop” - in which identical RNA loops bind each other through complementary sequences. Disrupting this interaction prevents disome formation, stunts cellular growth and makes cells more sensitive to stress.
Seeing ribosomes inside cells
A key strength of the study was the ability to visualize ribosomes directly inside intact cells using cryogenic electron tomography (Cryo-ET). Cryo-ET is a powerful 3D imaging technique that uses an electron microscope to see inside frozen biological samples (cells, organelles, molecules) with very high resolution. This approach allowed the team to visualize ribosomes in their native environment and resolve how they re-organize during stress.
The study combined an unusually broad range of techniques, including cell biology, biochemistry, yeast and mammalian cell genetic engineering, and high-resolution structural imaging. “One major challenge was manipulating ribosomal RNA, which is encoded by hundreds to thousands of nearly identical gene copies in animal genomes. We overcame this hurdle by engineering hybrid ribosomes in yeast and by introducing small RNA molecules that specifically disrupted ribosome pairing in animal cells”, says Mara Mueller, graduate student in the Schuman Lab and co-first author of the study.
A new view of translation control
„Our findings uncover a previously unknown mechanism by which animal cells regulate protein synthesis during stress - one that relies on RNA structure. The study reveals a new function for ribosomal RNA expansion segments which have been rather mysterious”, says Erin Schuman.
By temporarily storing ribosomes in inactive pairs, cells protect these costly machines and enable rapid recovery once favorable conditions return. The discovery opens new avenues for understanding how cells adapt to stress and how ribosome organization contributes to health and disease.
Prof. Dr. Erin Schuman
Director
Max Planck Institute for Brain Research
erin.schuman@brain.mpg.de
+49 69 850033-1001
Andre Schwarz*, Mara Mueller*, Helene Will, Lea Dietrich, Stefano L. Giandomenico, Georgi Tushev, Ina Bartnik, Iskander Khusainov, Claudia M. Fusco, Erin M. Schuman. rRNA expansion segments mediate the oligomerization of inactive animal ribosomes. Science (2026) *Co-first authors
http://www.science.org/doi/10.1126/science.adr4287
3D model of two rat hippocampal ribosomes interacting in a hibernating dimer via an RNA expansion se ...
Copyright: Max Planck Institute for Brain Research, 3D models: Oliver Döll.
Primary rat hippocampal neurons grown on an electron microscopy support grid prior to plunge-freezin ...
Copyright: Max Planck Institute for Brain Research / A. Schwarz
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