Single-Molecule Study Reveals Unexpected Role of Protein Stiffness in Nuclear Transport

Research from the Francis Crick Institute and King's College London indicates that the softness or rigidity of specific regions within proteins can influence how quickly or slowly those proteins enter the nucleus.

To perform various tasks, such as instructing the nucleus to turn on or off particular genes, proteins must enter and exit the nucleus, the cell's control center. These proteins pass through a channel known as the “nuclear pore complex” that is located on the outside of the nucleus.

This study, which was published in Nature Physics, adds to the body of evidence supporting the notion that mechanical characteristics can affect a protein's ability to enter a pore. Previously, studies have demonstrated that the size and composition of these proteins affect their ability to cross. 

By observing how proteins moved within single cells, the researchers were able to determine how quickly or slowly proteins could cross a given distance if their mechanical stability was close to their “nuclear-localization sequence,” which is a unique sequence that permits the protein to enter the nucleus.

They discovered that proteins adjacent to this sequence that possessed a soft or pliable region could enter the nucleus more rapidly.

Then, to facilitate the proteins’ easier entry into the nucleus, the researchers created a soft tag that could be inserted close to the sequence on stiffer proteins. 

This was investigated by tagging MRTF, a transcription factor that helps cells move throughout the body and activates specific genes. Cell movement was increased by attaching a soft tag to MRTF, allowing it to enter the nucleus more quickly.

The scientists think this might be a helpful tool for faster drug delivery to the nucleus or for tagging transcription factors to boost the activity of specific genes.

We’ve made a fundamental discovery that the mechanics of a protein – how soft or stiff it is in the region that leads translocation– control its entry into the cell’s nucleus. Although we only looked at the nuclear pore, this mechanism could regulate entry into other parts of the cell, such as the mitochondria or proteasomes. Knowing that a more flexible protein can enter the nucleus quicker could help us design more targeted drugs.”

Sergi Garcia-Manyes, Group Leader, Single Molecule Mechanobiology Laboratory, Francis Crick Institute

Sergi Garcia-Manyes is also the Professor of Biophysics at King’s College London.

Rafael Tapia-Rojo, Study Co-first Author and Former Postdoc, Crick, and Lecturer, Department of Biological Physics, King’s College London, said: “Our findings were rather unanticipated, and it was striking to see how measurements at the single molecule level can be so directly linked to what happens at a cellular level, using a newly designed optomechanical approach.”

Moving forward, scientists are examining how transcription factors have changed over time to acquire pliable regions that facilitate easier entry into the nucleus.