Disordered proteins assume a fluid-like state to fill the central channel of the nuclear pore, thereby forming the actual filtration system that regulates all transport into and out of the cell nucleus.
Illustration Credit: © Miao Yu and Karen Palacio-Rodríguez
Scientific Frontline: Extended "At a Glance" Summary: Transport Processes in Human Nuclear Pores
The Core Concept: The nuclear pore complex regulates the exchange of molecules between the cell nucleus and the cytoplasm through a central nanocanal. Recent in vivo measurements reveal that the intrinsically disordered proteins forming the selective barrier inside this canal exist in a highly mobile, fluid-like state.
Key Distinction/Mechanism: Unlike previous in vitro models that suggested the barrier proteins behave as rigid polymers, gummy gels, or solid condensates, living cells maintain the barrier's fluidity. This dynamic state is preserved by two critical factors: the presence of transport receptors and the glycosylation (sugar modification) of the barrier proteins, which prevents them from adhering too tightly.
Origin/History: Researchers from Johannes Gutenberg University Mainz, the Max Planck Institute for Biophysics, and Wuhan University published findings in Nature detailing the first measurement of intrinsic protein dynamics within the nuclear pore of a living cell.
Major Frameworks/Components:
- In Vivo Fluorescent Probing: The use of coupled fluorescent dyes to track the rapid mobility of proteins within the living cell's nuclear pore.
- Exascale Physicochemical Simulation: Comprehensive computational modeling, executed on the JUPITER supercomputer, to map the precise transport pathway.
- Edge Transport Routing: Simulations confirming that molecular transport primarily flows along the periphery of the pore, driven by physicochemical properties rather than a central biological plug.
- Protein Glycosylation: The biochemical modification of barrier proteins with sugar groups to maintain functional fluidity and prevent pathological aggregation.
Branches of Science: Synthetic Biophysics, Computational Biophysics, Cell Biology, Molecular Biology, and Structural Biology.
Future Application: The study's methodologies could be applied to map the flow dynamics of other molecular machines and to develop targeted therapies that prevent protein hardening in human cells.
Why It Matters: Understanding how the nuclear pore barrier remains fluid offers crucial insights into fundamental cellular function and the pathology of neurodegenerative diseases, such as Alzheimer's and Parkinson's, which are characterized by the abnormal hardening and aggregation of once-flexible proteins.
Our genetic material is hidden inside the nucleus of our cells, well protected by a double membrane. All molecules wishing to pass through must thread their way through one of several thousand nuclear pores. The scaffold structure of these pores is well known. However, exactly how transport takes place within them has been the subject of much debate. Researchers at Johannes Gutenberg University Mainz (JGU), the Max Planck Institute for Biophysics (MPI-BP) in Frankfurt am Main, and Wuhan University in China have now shed light on the matter. "For the first time, we have been able to measure intrinsic protein dynamics within the nanocanal of a living cell and demonstrate that the interior of this canal is fluid-like," stated Professor Edward Lemke, professor of synthetic biophysics at JGU, who led the current study together with Professor Gerhard Hummer from the MPI-BP. The researchers at the MPI-BP, in turn, have succeeded in creating the most comprehensive simulation model of a nuclear pore to date, based on the findings of Lemke and his team. In particular, this model answers the question of the transport pathway through the pore. "These complex calculations were made possible by JUPITER, Europe's first exascale supercomputer at the Jülich Research Center," said Hummer. The researchers published their findings in Nature. "As the nuclear pore protects the genome and controls all exchange between the cell nucleus and the cytoplasm, it is one of the most important molecular machines in the human cell," emphasized Professor Miao Yu from Wuhan University, co-first author of the study. "And also one of the most complex," added co-first author Maziar Heidari from the MPI-BP.
Fluorescent Dyes as Probes The nuclear membrane surrounds the interior of human cell nuclei, protecting genetic information. Signaling molecules and pathogens must pass through nuclear pores, which control the passage of tens of thousands of molecules per minute. While certain molecules are specifically permitted to pass, others are held back. Essential to this selection process is a barrier of proteins that fills the opening—that much was already known. However, opinions differed widely regarding the exact nature of this barrier: studies on isolated proteins yielded varying results, ranging from stretched polymers to liquid-like condensates and even solid-like gels exhibiting high viscoelastic resistance. "Such studies did not, however, allow any direct conclusions to be drawn about how the barrier behaves within the living cell," said Lemke. The exact rheological properties of these anchored protein chains within their natural environment—specifically whether they behave as rigid structures, viscoelastic fluids, or true liquids—and the extent to which their dynamics contribute to selective transport, remained undetermined until now.
To find those answers, Lemke and his team specifically coupled fluorescent dyes to the proteins in the nuclear pores as probes: tiny glowing dots whose mobility reveals a great deal about the dynamics of the proteins. "As the dyes move extremely quickly, the state inside the nuclear pores must be fluid-like," explained Lemke.
What Keeps the Barrier Fluid In living cells, the proteins remained highly mobile throughout the entire two-hour observation period. The team compared these results with an in vitro model, i.e., with isolated proteins in a test tube. There, however, after about two hours, the protein mass invariably turned into a rigid structure or even a solid state resembling the pathological protein aggregates characteristic of neurodegenerative diseases such as Alzheimer's or Parkinson's. "This was a crucial turning point: there had to be something keeping the barrier in the cells dynamic," said Lemke. The researchers determined that maintaining this dynamic state requires two factors: the presence of transport receptors, and the glycosylation of barrier proteins—that is, modification with sugar groups—so that they do not stick together too tightly. "When we add these two components, we observe a similar mobility in the model system to that found in the nuclear pores of living cells," stated Lemke.
Transport Primarily via the Edge of the Pore Another unresolved question concerned the transport pathway. While the flow velocity in pipes or rivers, for example, is higher in the center than at the edges, earlier studies suggested that the opposite is true in nuclear pores. The scientific community's hypothesis was that there must be a biological reason for this, such as a plug in the center of the pore. The researchers led by Hummer carried out simulations to investigate this. They based their work on the degree of cross-linking that the Mainz team had determined in their experiments. "The simulations confirm that the main transport route runs along the edge of the pore," said Hummer. "While we do not rule out a biological cause such as a plug, it is not necessary from a physicochemical point of view." The findings are not only important for a fundamental understanding of how human cells function, but also help to shed light on neurodegenerative processes, as these also involve the hardening of previously flexible proteins.
Funding: M.Y. acknowledges funding from the National Key Research and Development Program of China (grant no. 2025YFA1309700), the National Natural Science Foundation of China (grant no. 32471521), the Fundamental Research Funds for the Central Universities (grant no. 2042025kf0029) and Hubei Provincial Natural Science Foundation of China (grant no. 2025AFA021). E.A.L. acknowledges funding from the ERC-ADG grant ‘MultiOrganelleDesign’, as well as CRC1551 ‘Polymer concepts in cellular function’ of the Deutsche Forschungsgemeinschaft (DFG project no. 464588647). E.A.L. and G.H. acknowledge funding from CRC 1507 ‘Membrane-associated protein assemblies, machineries and supercomplexes’ and SCALE of the Deutsche Forschungsgemeinschaft (DFG project no. 450648163, 533751785). M.H., K.P.-R. and G.H. thank the Max Planck Society for support. M.S. and A.A.H. are supported under Dioscuri, a programme initiated by the Max Planck Society, jointly managed with the National Science Centre in Poland and mutually funded by the Polish Ministry of Education and Science and the German Federal Ministry of Education and Research. K.P.-R. acknowledges support from the ‘Hessen Horizon Marie Skłodowska-Curie-Stipendium’ program. This project received access to the JUPITER supercomputer, which is funded by the EuroHPC Joint Undertaking, the German Federal Ministry of Research, Technology and Space and the Ministry of Culture and Science of the German state of North Rhine-Westphalia, through the JUPITER Research and Early Access Program (JUREAP). Open access funding provided by Johannes Gutenberg-Universität Mainz.
Published in journal: Nature
Title: Glycosylation and importins liquefy the FG barrier in live nuclear pores
Authors: Miao Yu, Maziar Heidari, Karen Palacio-Rodriguez, Hao Ruan, Sara Mingu, Yu Chen, Xu-Zhuo Gou, Pingkai Shen, Songzi Liu, Si-Yu Chen, Alam Ahmad Hidayat, Mathis Bode, Mateusz Sikora, Ai-Hui Tang, Gerhard Hummer, and Edward A. Lemke
Source/Credit: Johannes Gutenberg University Mainz
Edited by: Scientific Frontline
Reference Number: biph111326_01