Kanazawa University Research

Real-time Monitoring of Proteins in the Nuclear Pore Complex

KANAZAWA,Japan, June 30, 2020 /PRNewswire/ -- Researchers at Kanazawa University report in Biomaterials a high-speed atomic-force microscopy study of protein filaments in the nuclear pore complex.  The visualization in real-time of the filaments' dynamics is an important step in our understanding of molecular transport mechanisms between a cell nucleus and its surrounding medium.

In human cells, the nucleus is enclosed by a structure called the nuclear pore complex (NPC).  It acts as a 'gatekeeper' controlling the transport of molecules between the nucleus and the surrounding cytoplasm (the protein-containing solution in the inside of a cell).  The NPC consists of proteins known as nucleoporins; some of these, the so-called FG-NUPs, belong to the class of intrinsically disordered proteins (IDPs) and capable of forming liquid-–liquid phase separation (LLPS), lacking a well-defined tertiary structure (that is, a particular 3D shape).  Although a lot is known about FG-NUPs, a thorough understanding of how their structure varies in time and space has been missing.  But now, by applying high-speed atomic force microscopy (HS-AFM), Richard Wong from Kanazawa University and colleagues provide much-needed insights into the spatiotemporal structure of FG-NUPs.

The technique used by the researchers, HS-AFM, is typically used for imaging surfaces.  A tiny cantilever is made to move over the surface; at any given time, the force experienced by the cantilever probe can be converted into a height measure.  A scan of the whole surface then results in a height map of the sample.  By repeatedly scanning the surface rapidly, a video of its evolving structure is obtained.  Applying HS-AFM to FG-NUPs, Wong and colleagues were able to measure several of the molecules' properties, including the extension velocity of FG-NUP filaments (thread-like protruding structures), their bending angles and how they form knots.

The scientists studied FG-NUPs in normal colon cells and in colorectal cancer cells and organoids.  They found that the former displayed less conformational dynamics.  A particularly interesting conclusion is that in colon cancer cells, the structure of the so-called central plug is smaller, and cannot develop filamentous features as easily as in normal cells, a finding with high clinical relevance.