Nuclear Pore's Architecture Revealed Directly in Cells
In order to enter a concert or sporting event held at a large stadium, one must often battle through crowds of fellow fans, find the correct entrance, and present a security guard with a valid ticket. A similar scenario takes place at the molecular level as proteins and other molecules attempt to reach the nucleus of the eukaryotic cell. The cell’s nuclear pore complexes act as the nuclear envelope’s security guards controlling which proteins and molecules are granted access to travel to and from the nucleus; only those with the correct “ticket” are permitted to pass.
To initiate infection, many viruses such as influenza, herpes and SARS-CoV-2 must first breach the nuclear pore complex. CSSB scientists in Jan Kosinski’s group seeks to understand the structure of the entire nuclear complex, its dynamics and interactions with viruses. Using structural biology microscopic techniques combined with integrative modeling, Kosinski and his collaborator Martin Beck, Max Planck Institute of Biophysics and EMBL Heidelberg, recently revealed the cell architecture of the yeast nuclear pore and snapshots of its turnover in Nature.
Using cryo-electron tomography, a technique that enables the observation of molecular machines at work in their native environment, Martin Beck’s group was able to image yeast’s nuclear pore complex directly in the cell. “Our cyro-EM map has a resolution of approximately 25 Å,” explains Beck “this provides us with more accurate and precise information than previous EM maps which relied on data from complexes purified with detergents.” The cryo-EM map allowed the Beck group to identify in situ both the conformation and configuration of nucleoporin subcomplexes including Nup159; a complex that, in humans, is known to be a common point of attack for viruses.
The Kosinski group used their integrative modeling pipeline to build models of the yeast nuclear pore. “With data from the detailed cryo-EM maps, we built a model that is not only more detailed than previous ones, but also displays the Nup159 complex’s revised orientation,” explains Vasileios Rantos, a PhD student in the Kosinski group who performed the modeling, “this helps us to explain Nup159’s role in RNA export and provides insight into how viruses may interact with this part of the nuclear pore complex.” Further analysis of perturbed yeast cells performed by Beck group in collaboration with Pfander group (Max Planck Institute of Biochemistry) also demonstrated that this revised orientation explains Nup159 role in enabling autophagy of nuclear pores through the so-called nuclear envelope hernia.
The elucidation of Nup159’s role in both RNA export and autophagy in yeast brings the scientists a step closer to understand how these interactions might occur in human cells. “Many viruses including influenza virus and SARS-CoV-2 are known to interact with this subcomplex,” explains Kosinski “therefore understanding the human nuclear pore complex’s structure and mechanisms helps us understanding how viruses disrupt and interfere with this system.”
Allegretti, M., Zimmerli, C.E., Rantos, V. et al. (2020) In-cell architecture of the nuclear pore and snapshots of its turnover. Nature. doi.org/10.1038/s41586-020-2670-5